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Synthesis and structures of hydride-bridged palladium A-frame complexes
www.elsevier.nl/locate/ica Inorganica Chimica Acta 300 – 302 (2000) 395 – 405
Synthesis and structures of hydride-bridged palladium A-frame complexes Robert A. Stockland Jr., Gordon K. Anderson *, Nigam P. Rath Department of Chemistry, Uni6ersity of Missouri-St. Louis, 8001 Natural Bridge Road, St. Louis, MO 63121, USA Received 22 September 1999; accepted 7 December 1999
Abstract A series of hydride-bridged palladium A-frame complexes [Pd2R2(m-H)(m-dppm)2]PF6 has been prepared by reaction of [Pd2Cl2(m-dppm)2] with 2 equiv. of a Grignard reagent, followed by addition of CBr4, NaBH4 and TlPF6. The mixed palladium–platinum species [PdPtR2(m-H)(m-dppm)2]PF6 were generated analogously from [PdPtCl2(m-dppm)2], whereas the unsymmetrical dipalladium derivatives [Pd2(Mes)R(m-H)(m-dppm)2]PF6 were produced from the reaction of [Pd(Mes)(dppm)2]X with [Pd2R2(m-Cl)2(AsPh3)2], followed by treatment with NaBH4. The complexes were characterized by elemental analysis, 1H and 31 P NMR spectroscopy. The solid-state structures of [Pd2(C6H4Me-4)2(m-H)(m-dppm)2]BH3CN (1a) (obtained as its BH3CN− salt when NaBH3CN was used instead of NaBH4), [PdPt(C6H4Me-4)2(m-H)(m-dppm)2]PF6 (2a), [Pd2(Mes)Et(m-H)(m-dppm)2]PF6 (3b), [Pd2(Mes)Ph(m-H)(m-dppm)2]PF6 (3c) and [EtPt(m-H)(m-dppm)2PdMe]PF6 (4) have been determined by X-ray crystallography. 3c adopts an elongated boat conformation in the solid state, whereas the others exist in the chair form. The unsymmetrical cations 2a and 4 containing smaller organic substituents are disordered in the solid state, whereas the mesityl-containing derivatives 3b and 3c are not. © 2000 Elsevier Science S.A. All rights reserved. Keywords: Crystal structures; Hydride-bridged complexes; Palladium complexes
1. Introduction The chemistry of transition metal complexes bridged by dppm or related ligands is now extensive [1–3]. Dimeric and trimeric palladium and platinum species, in particular, are numerous. The dimeric complexes typically contain two bridging diphosphines, and include ‘side-by-side’ derivatives containing a metal– metal bond, trans,trans and cis,cis complexes with no other bridging groups, and A-frames in which there is one additional bridging group. Although A-frame complexes of these metals are well known, those containing a hydride as the additional bridging moiety are relatively few, and only two have been characterized crystallographically (vide infra). The platinum trihydride [Pt2H2(m-H)(m-dppm)2]+ was generated by Puddephatt and co-workers by NaBH4 * Corresponding author. Tel.: + 1-314-516 5311; fax: + 1-314-516 5342. E-mail address: [email protected] (G.K. Anderson)
reduction of [PtCl2(dppm)] [4–6], and the related complexes [Pt2HMe(m-H)(m-dppm)2]+ and [Pt2R2(m-H)(mdppm)2]+ (R=Me, Et) have also been prepared [7–9]. We have shown that unsymmetrical hydride-bridged platinum complexes may also be prepared by reaction of [PtR(dppm-PP)(dppm-P)]+ with [PtClR%(cod)], followed by reduction to give [RPt(m-H)(m-dppm)2PtR%]+, and this methodology may be extended to mixed platinum–palladium species [10,11]. The first hydridebridged palladium A-frame was described by Stille and co-workers, formed by the reaction of [Pd2Cl2(mdppm)2] with Me3Al, followed by NaBPh4 and ethanol [12], although they reported it to be thermally unstable. We have reported that the chloride-bridged palladium A-frames [Pd2R2(m-Cl)(m-dppm)2]+ may be reduced with NaBH4 or NaBH3CN to generate the corresponding hydride-bridged complexes [13]. We found these to be quite stable at ambient temperature, although they do undergo elimination reactions at elevated temperatures [14].
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The platinum complex [Pt2Me2(m-H)(m-dppm)2]PF6 was characterized by X-ray crystallography, although the bridging hydride was not located [8]. We reported the solid-state structure of the ethylpalladium derivative [Pd2Et2(m-H)(m-dppm)2]PF6, in which the ethyl groups and bridging hydride were disordered over two positions [13]. These represent the only two structures of hydride-bridged A-frame complexes of the Group 10 metals reported to date. In this paper we report the synthesis of palladium and mixed metal A-frame complexes, and the solid-state structures of five hydridebridged derivatives. 2. Results and discussion We have shown that hydride-bridged organopalladium A-frames are generally available by replacement of a bridging halide using NaBH4. The halide-bridged derivatives [Pd2R2(m-X)(m-dppm)2]+ may be prepared from reactions of [PdClR(cod)] (R= Me, Bn) or [Pd2R2(m-Cl)2(AsPh3)2] (R= Me, Et, Bu, Ph) with dppm [13], and we have extended this to the acylpalladium species [Pd2(COR)2(m-X)(m-dppm)2]+ (R =Me, Et, Bn) by reacting the chloride-bridged arsine dimers with CO prior to the introduction of dppm. Alternatively, halide-bridged compounds may be obtained by treatment of [PdX2(dppm)] with a Grignard reagent (R= Me, Et, Bu, CH2SiMe3, Bn, Mes) [15]. These methods are not generally applicable to complexes with aryl substituents, however. We have now developed a more versatile approach that may be used with aryls, as well as with a range of alkyl groups, starting from the palladium(I) precursor [Pd2Cl2(m-dppm)2], as outlined in Scheme 1. Synthesis of the halide-bridged species by this method will be described in detail elsewhere, but a brief synopsis will be provided here.
Reaction of [Pd2Cl2(m-dppm)2] with an excess of the appropriate Grignard reagent in CH2Cl2 solution at low temperature generated [Pd2R2(m-dppm)2] which, on treatment with CBr4, resulted in nearly quantitative formation of the bromide-bridged A-frame. Addition of a solution of NaBH4 at low temperature provided quantitative conversion to the hydride-bridged species, 1a–e, which may also be isolated conveniently as their PF6− salts. The acyl species [Pd2(COR)2(m-H)(mdppm)2]PF6 (R=Me, Et, Bn), 1f–h, were generated by reaction of [Pd2R2(m-Cl)2(AsPh3)2] with CO and dppm, followed by NaBH4. The mixed metal complexes 2a,b could be obtained starting from [PdPtCl2(m-dppm)2] [16] according to the procedure outlined in Scheme 2. The above systems permit only the synthesis of complexes in which the two terminal organic groups are identical. We had previously prepared a range of platinum-containing dppm-bridged species using the [PtR(dppm-PP)(dppm-P)]+ precursors [10,11,17–19], obtained by treating [PtClR(cod)] with 2 equiv. of dppm. With palladium, however, dimerization of the [PdClR(dppm)] intermediate is much faster than coordination of the second dppm ligand, except with the very bulky mesityl system. In this case, reactions of the [Pd(Mes)(dppm-PP)(dppm-P)]+ cation with [Pd2R2(mCl)2(AsPh3)2] (R= Me, Et, Ph) at low temperature gave the unsymmetrical A-frames [Pd2(Mes)R(m-X)(mdppm)2]+ in excellent yield as mixtures of chloride- and bromide-bridged species. These were not isolated, but further reaction with NaBH4 gave the hydride-bridged derivatives, 3a–c (Scheme 3), which were again isolated as their PF6− salts. The hydride-bridged A-frame complexes were isolated as colorless to light-brown powders. In the solid state they could be stored for several weeks without discoloration in the absence of light; if kept below
Scheme 1.
Scheme 2.
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Scheme 3.
− 40°C no signs of decomposition could be observed over more extended time periods. Dichloromethane solutions of the complexes could be stored below − 40°C for several weeks without significant discoloration, but decomposition occurred over longer periods. Incorporation of platinum in 2, or the bulky mesityl group in 3, affords greater thermal stability to the hydride-bridged complexes. The 31P{1H} NMR spectra of the symmetrical complexes 1 each exhibit a single resonance, the alkyl complexes appearing at slightly higher frequencies than the aryls, and shifted by approximately 5 ppm to high frequency of their halide analogues. The unsymmetrical palladium species 3 give rise to two multiplets due to the presence of two pairs of equivalent P atoms. The chemical shifts of the P atoms attached to palladium and platinum in 2a,b are coincidentally identical, so a single resonance is observed with 195Pt satellites of approximately half the usual intensity. The 1H NMR spectra of the hydride complexes contain the expected resonances due to the terminal organic fragments. In each case the CH2 groups of the dppm ligands give rise to one broad multiplet in the range 3.9 – 4.7 ppm, the methylene hydrogens being equivalent due to rapid inversion of the A-frame structure [20]. The bridging hydride appears as a quintet in each case, due to coupling to the four P atoms (in the unsymmetrical compounds the two 2J(P,H) values are identical), between − 7.5 and − 10.3 ppm. The position of the hydride resonance depends significantly on the nature of the terminal organic groups, being around − 9.1 ppm in the aryl derivatives 1a,b, between − 7.5 and − 7.8 ppm in the alkyl complexes 1c – e, and between − 10.0 and −10.3 ppm in the acyls 1f –h. The introduction of one platinum for palladium in 2a,b has little effect on the chemical shift of the hydride. In the unsymmetrical palladium complexes, the introduction of a mesityl group causes the hydride to be slightly more shielded in 3a,b compared to 1c,d, whereas in 3c it is less shielded than in the corresponding diphenyl complex 1b. The mesityl-containing compounds 3 each exhibit two resonances in a 2:1 ratio, due to the two ortho and one para methyls. Thus, the two ortho methyl groups are equivalent. This could arise due to free rotation about the Pd-mesityl bond, or because the two faces of the Pd2P4 core are equivalent on the NMR time
scale. The latter is more likely because rotation about the Pd-mesityl bond is slow in the bromide-bridged complex [Pd2(Mes)2(m-Br)(m-dppm)2]PF6 [15]. We reported previously the solid-state structure of [Pd2Et2(m-H)(m-dppm)2]PF6 (1d) [13], the first example of a hydride-bridged palladium A-frame complex to be characterized by X-ray crystallography. In the cation, the ethyl groups and bridging hydride were disordered over two sites, and the eight-membered Pd2P4C2 ring adopted an elongated chair conformation. Here we report the structures of a further five hydride-bridged A-frames, namely (1a) (as its BH3CN− salt), 2a, 3b, 3c and [EtPt(m-H)(m-dppm)2PdMe]+ (4) [10] (as their PF6− salts). [Pd2(C6H4Me-4)2(m-H)(m-dppm)2]BH3CN(1a·BH3CN), crystallized in the P1( space group as orange plates from CH2Cl2 –pentane solution at − 40°C. Although TlPF6 was added in order to replace the counterion, incomplete conversion to the hexafluorophosphate salt took place in this case, and crystallization as the cyanoborohydride (which is disordered) occurred. The molecular structure of the cation is shown in Fig. 1, and selected bond distances and angles are presented in Table 1. The are no close contacts between the cation and BH3CN−. The cation comprises of two Pd atoms linked by two dppm ligands and a hydride, and two terminal tolyl groups. The PdPd distance is 3.0758(4) A, , indicating
Fig. 1. Projection view of the molecular structure 1a showing the atom-labeling scheme, with non-hydrogen atoms represented by 50% probability ellipsoids.
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Table 1 Selected bond distances (A, ) and angles (°) for 1a·BH3CN PdPd% PdP(2)
3.0758(4) 2.2936(7)
PdP(1) PdC(3)
2.3030(7) 2.032(3)
P(1)PdP(2) P(2)PdC(3) P(1)PdPd%
175.97(3) 90.51(8) 91.43(2)
P(1)PdC(3) C(3)PdPd% P(2)PdPd%
88.87(8) 178.41(9) 89.08(2)
Fig. 2. Projection view of the molecular structure of 2a showing the atom-labeling scheme, with non-hydrogen atoms represented by 50% probability ellipsoids. Table 2 Selected bond distances (A, ) and angles (°) for 2a PdPt PdP(2) PtP(4) PtC(34)
3.0126(7) 2.287(2) 2.291(2) 2.095(10)
PdP(1) PtP(3) PdC(3)
2.285(2) 2.292(2) 2.055(10)
P(1)PdP(2) P(1)PdC(3) P(3)PtC(34) C(3)PdPt
175.21(9) 89.0(3) 91.0(3) 170.9(3)
P(3)PtP(4) P(2)PdC(3) P(4)PtC(34) C(34)PtPd
178.28(9) 88.1(3) 88.0(3) 167.6(3)
that there is no significant metal – metal interaction. The PPdP angles approach linearity (175.97(3)°); the PdP distances are unremarkable and almost identical. The tolyl ligands lie trans to the bridging hydride, and the PdC distance is 2.032(3) A, . As found for [Pd2Et2(m-H)(m-dppm)2]+, the cation crystallizes in an eight-membered elongated chair conformation, with the dppm CH2 groups lying on opposite faces of the Pd2P4 plane. The PPdPdP torsion angles are 4.0°, indicating that the PPdP vectors are nearly parallel and the Pd2P4 unit is nearly planar (as is the case for the ethylpalladium cation [13]). The most remarkable feature of the structure is the almost perfectly linear nature of the CPdPdC unit, the CPdPd angles being 178.44(9)°. Such a linear RMHMR species has been proposed as the intermediate in the fluxional
process that equilibrates the faces of a hydride-bridged A-frame complex [20], and the present structure would represent the capturing of that intermediate in the solid state. The mixed metal complex [PdPt(C6H4Me-4)2(m-H)(mdppm)2]PF6 (2a) crystallized from CDCl3 –Et2O solution as colorless needles in the monoclinic space group P21/n. The asymmetric unit contained a CDCl3 molecule per molecule of 2a. The molecular structure of the cation is shown in Fig. 2, and selected bond lengths and angles are given in Table 2. The structure is disordered over the two metal positions, and the refinement was carried out using 50% occupancy of each metal in each of the two sites. Such disorder is perhaps unsurprising because the covalent radii of palladium and platinum are nearly identical. The cation consists of the metals connected via two dppm ligands and the bridging hydride, and two terminal tolyl moieties. The metal–metal distance of 3.0126(7) A, again suggests the lack of any significant interaction. The MP distances are unsurprising, and the PMP angles are 175.21(9) and 178.28(9)°. The cation again crystallizes in an elongated chair conformation. The CMM% angles are 170.9(3) and 167.6(3)°, and the PMMP torsion angles of 2.5 and 3.0° show that the PMP vectors are again almost parallel. Orange cuboids of [Pd2(Mes)Et(m-H)(m-dppm)2]PF6 (3b) were obtained from CH2Cl2 –Et2O solution. The compound crystallized in the space group C2/c. No solvent molecules were incorporated into the unit cell and the structure was not disordered. In fact, this represents the first unsymmetrical palladium or platinum hydride-bridged A-frame complex that is not disordered. The molecular structure of the cation is shown in Fig. 3 and selected bond distances and angles are presented in Table 3. The cation consists of two Pd
Fig. 3. Projection view of the molecular structure of 3b showing the atom-labeling scheme, with non-hydrogen atoms represented by 50% probability ellipsoids.
R.A. Stockland Jr. et al. / Inorganica Chimica Acta 300–302 (2000) 395–405 Table 3 Selected bond distances (A, ) and angles (°) for 3b Pd(1)Pd(2) Pd(1)P(2) Pd(2)P(4) Pd(2)C(3)
2.9302(8) 2.291(2) 2.278(2) 2.115(7)
Pd(1)P(1) Pd(2)P(3) Pd(1)C(5)
2.330(2) 2.324(2) 2.071(8)
P(1)Pd(1)P(2) P(2)Pd(1)C(5) P(3)Pd(2)C(3) C(5)Pd(1)Pd(2)
166.70(8) 87.8(2) 91.2(2) 147.0(2)
P(1)Pd(1)C(5) P(3)Pd(2)P(4) P(4)Pd(2)C(3) C(3)Pd(2)Pd(1)
96.3(2) 173.10(8) 85.2(2) 158.5(2)
Table 4 Selected bond distances (A, ) and angles (°) for 3c Pd(1)Pd(2) Pd(1)P(2) Pd(2)P(4) Pd(2)C(12)
2.9836(6) 2.312(2) 2.303(2) 2.030(7)
Pd(1)P(1) Pd(2)P(3) Pd(1)C(3)
2.292(2) 2.301(2) 2.052(7)
P(1)Pd(1)P(2) P(2)Pd(1)C(3) P(3)Pd(2)C(12) C(3)Pd(1)Pd(2)
178.61(6) 88.5(2) 90.1(2) 156.6(3)
P(1)Pd(1)C(3) P(3)Pd(2)P(4) P(4)Pd(2)C(12) C(12)Pd(2)Pd(1)
90.3(2) 175.39(6) 87.0(2) 165.3(2)
atoms linked by two dppm ligands and the bridging hydride, one Pd atom being ligated by the mesityl ring and the other by the ethyl group. The PdPd distance is 2.9302(8) A, , shorter than that in either of the cations described above. The cation again adopts an elongated chair conformation. The PdP bond lengths are not identical, with each Pd atom having one shorter and one longer PdP distance. The PPdPdP torsion angles are 9.1 and 10.6°, indicating that the Pd2P4 unit is more twisted than in the other hydride-bridged palladium complexes. The PdC distance is slightly shorter for the mesityl group than for ethyl. A number of features of the structure are likely results of the presence of a bulky substituent on one palladium. The mesityl ring lies almost perpendicular to the Pd2P4 unit, as previously found for the bromide-bridged complex [Pd2(Mes)2(m-Br)(m-dppm)2]PF6 [15]. The PPdP angles are 166.70(8) and 173.10(8)°, the greater deviation from linearity being at the mesitylpalladium center. The EtPdPd angle is 158.5(2)°, almost identical to that found in [Pd2Et2(m-H)(m-dppm)2]+ [13], whereas the MesPdPd angle is significantly smaller at 147.0(2)°. Although one might expect a more linear MesPdPd fragment, in which the bulky group points directly away from the second metal center, to be sterically favored, the bending of the PPdP axis and the perpendicular orientation of the mesityl ring allow it to adopt a smaller angle such that the ring lies between the dppm phenyl groups. The bridging hydride was located from the residual electron density map and successfully refined. Although too much confidence should not be placed on the position of a single hydrogen atom, the
399
refined position does reflect the unsymmetrical nature of the complex. The PdH distances are 1.53 and 1.96 A, , the shorter distance being trans to the ethyl fragment. Complex [Pd2(Mes)Ph(m-H)(m-dppm)2]PF6 (3c) was obtained as pale-yellow crystals by slow evaporation of a CH2Cl2 –C6H6 –Et2O solution. The compound crystallized in the space group P21/n, with 2.5 benzene molecules per molecule of 3c. Again, the structure was not disordered. The molecular structure of the cation is shown in Fig. 4 and selected bond distances and angles are presented in Table 4. The cation consists of two Pd atoms linked by two dppm ligands and a bridging hydride, the mesityl ring being coordinated to one Pd atom and the phenyl group to the other. The PdPd distance is 2.9836(6) A, , slightly longer than that in 3b. In contrast to all of the examples previously discussed, this cation adopts an elongated boat conformation with both dppm CH2 groups oriented on the same face of the Pd2P4 plane, and opposite the mesityl and phenyl substituents. The PdP bond lengths involving the phenylpalladium center are identical, but the mesitylpalladium center has PdP distances that differ by 0.02 A, . The PPdPdP torsion angles are 9.5 and 13.8°, indicating that the Pd2P4 unit is again significantly twisted from planarity. As in 3b, the mesityl ring lies almost perpendicular to the Pd2P4 unit. The distortion from square planar geometry at the mesitylpalladium center seen in 3b is not found here, the PPdP and PPdC angles being 178.61(6), 88.5(2) and 90.3(2)°, respectively. The MesPdPd and PhPdPd angles are 156.6(3) and 165.3(2)°, respectively, indicating that the central core of the cation is flatter than that in 3b. The structure of the mixed metal complex [EtPt(mH)(m-dppm)2PdMe]PF6 (4), prepared previously from [PtEt(dppm-PP)(dppm-P)]PF6 and [PdClMe(cod)] [10], was also determined. The compound crystallized as
Fig. 4. Projection view of the molecular structure of 3c showing the atom-labeling scheme, with non-hydrogen atoms represented by 30% probability ellipsoids.
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400
Fig. 5. Projection view of the molecular structure of 4 showing the atom-labeling scheme, with non-hydrogen atoms represented by 50% probability ellipsoids. Table 5 Selected bond distances (A, ) and angles (°) for 4 PdPt PtP(2) PdC(26%)
2.9088(10) 2.276(2) 2.20(3)
PtP(1) PtC(26)
2.299(2) 2.02(2)
P(1)PtP(2) P(2)PtC(26) P(2%)PdC(26%) C(26%)PdPt
175.95(9) 85.5(5) 88.8(5) 167.1(12)
P(1)PtC(26) P(1%)PdC(26%) C(26)PtPd
90.5(5) 87.5(5) 164.8(6)
light-orange crystals from CHCl3 solution in the space group P1( with two solvent molecules per A-frame unit. The molecular structure of the cation is shown in Fig. 5 and selected bond distances and angles are given in Table 5. Like 2a, the structure is disordered over the two metal positions, as well as their attached alkyl substituents, and refinement was performed using 50% occupancy of each alkylmetal fragment in each site. The cation crystallizes as an elongated chair, with a PdPt distance of 2.9088(10) A, , the shortest among the hydride-bridged A-frames studied. The PMP angles are close to 180°, and the CMM angles are 164.8(6)
and 167.1(12)°. The PMMP torsion angles are only 0.9°, showing that the central framework is almost perfectly planar. There are a number of noteworthy features of these hydride-bridged complexes, and some pertinent structural data are listed in Table 6. The ‘hydride’ bridge may be considered as a protonated metal–metal bond (although attempts to generate the cations by this route have met only with limited success) and, as such, involves a three-center two-electron bond. The metal– metal distances range from 2.9088(10) to 3.0759(7) A, for the hydride-bridged A-frames reported (Table 6). These are all relatively long compared with the distances found in metal–metal bonded palladium(I) species [21], but they lie at the shorter end of the range of distances found for other palladium A-frame derivatives [15]. The longest PdPd distances are found for 1a, which has an almost linear CPdPdC core, and its mixed metal analogue 2a. There is no clear dependence of PdPd distance on the bending of the central core or on the size of the terminal organic substituents. Indeed, the bulky mesityl-containing complex 3b exhibits one of the shortest distances; it also has the most bent central core and one of the two (along with 3c) significantly twisted Pd2P4 units. Another curious feature is that 3c adopts an extended boat conformation in the solid state, whereas all the other hydride-bridged derivatives are chairs. The observation of only one hydride signal and a single, broad resonance for the dppm CH2 groups in the 1H NMR spectra indicates that inversion of the A-frame, and interconversion of chair and boat conformations, is rapid on the NMR time scale. Since this fluxional process cannot be arrested even at −90°C it is impossible to determine the relative concentrations of the chair and boat conformations in solution. Thus, the isolation of one or the other may be entirely fortuitous, or it might indicate a predominance of one form in solution (although it need not be the major species in solution that begins to crystallize first). For the mesityl-containing complexes 3b and 3c, one is found as a chair and the other as a boat in the solid state, and this might lead us to speculate that both forms are present in nearly equal concentrations in solution (Fig. 6). In
Table 6 Selected structural data for the [RM(m-H)(m-dppm)2M%R%]+ cations
4 3b 3c 1d 2a 1a
R
M
M%
R%
MM% (A, )
MM%R% (°)
RMM% (°)
Ref.
Me Mes Me Mes Et 4-tol 4-tol
Pd Pd Pt Pd Pd Pd Pd
Pt Pd Pt Pd Pd Pt Pd
Et Et Me Ph Et 4-tol 4-tol
2.9086(10) 2.9302(8) 2.932(1) 2.9836(6) 2.9933(7) 3.0126(7) 3.0758(7)
165.0(5) 158.5(2) 161.794 165.3(2) 159.4(3) 167.6(3) 178.44(7)
167.9(5) 147.0(2) 169.413 156.6(3)
this this [8] this [13] this this
170.9(3)
work work work work work
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401
Fig. 6. Views of the central cores of 3b and 3c to illustrate the elongated chair and boat conformations.
contrast, when the complex contains smaller organic groups on palladium the chair form may predominate in the crystallizing solution, and only chair conformations are found in the solid state. In the boat structure 3c each of the equatorial hydrogens of the dppm methylene groups exhibits a somewhat short distance (3.47 and 3.52 A, ) to the centroid of a dppm phenyl ring of an adjacent molecule, whereas the axial hydrogens show intramolecular CH···centroid distances of 3.83 and 3.94 A, . Each of the chair complexes has only the longer methylene CH···centroid distances (intra- and/or intermolecular) in the range 3.79–3.94 A, . In addition, complexes 2a, 3b, 3c and 4 exhibit hydrogen bonding between dppm phenyl hydrogens and the PF6− anions, with H···F distances lying in the range 2.37 – 2.81 A, . There are also relatively short H···F contacts involving the C6H6 solvent in 3c (2.34 and 2.49 A, ) and the CHCl3 molecule in 4 (2.35 and 2.47 A, ). There is no obvious hydrogen bonding in the structure of 1a. As pointed out above, the mesityl-containing Aframes are the only unsymmetrical hydride-bridged derivatives that are not disordered. Consideration of space-filling models of the complexes reveals that the shape of the cation is dominated by the dppm phenyl groups; between the phenyls are two cavities that may be occupied by the metals and the terminal organic moieties. Palladium and platinum are almost identical in size, so incorporation of one or the other will have a minimal effect on the periphery of the cation. When two smaller organic groups are involved (in 4 for example) neither cavity is filled completely and the ‘ends’ of the A-frame appear to be similar. In 3b and 3c the bulky mesityl group fills one of the cavities, whereas the ethyl or phenyl group does not, and the two ‘ends’ of the structure are readily distinguishable. Recognition of this difference during the crystallization process should lead to an ordered structure, as is found to be the case. Where the two ends appear similar, crystallization in either orientation can occur, and hence a disordered structure may be obtained.
3. Experimental All reactions were carried out under an argon atmosphere. [PdCl2(cod)], [Pd2Cl2(m-dppm)2] and [PdPtCl2(mdppm)2] were prepared by reported methods [16,22,23]. Grignard reagents were purchased from Aldrich. 1H and 31P{1H} NMR spectra were recorded on a Varian Unity plus 300 or Bruker ARX-500 spectrometer. Chemical shifts are relative to the residual solvent resonance or external H3PO4 respectively, positive shifts representing deshielding. The following abbreviations are used: s = singlet, t =triplet, q = quintet, m =multiplet. Microanalyses were performed by Atlantic Microlab, Norcross, GA.
3.1. Preparation of [Pd2(C6H4Me-4)2(m-H)(m-dppm)2]PF6 (1a) A stirred CH2Cl2 solution (30 ml) of [Pd2Cl2(mdppm)2] (0.10 g, 0.095 mmol) was cooled to −78°C, and 4-tolylmagnesium bromide (1.0 ml of a 1.0 M solution in ether) was added. The solution turned an intense dark-red color, and was stirred for 5 h. Methanol (1 ml), CBr4 (0.10 g, 0.30 mmol), and TlPF6 (0.034 g, 0.097 mmol) were added and the flask was allowed to warm to ambient temperature while the solvents were removed under reduced pressure. After washing with ether and hexane, the solid residue was extracted with CH2Cl2 and passed through a 5-cm neutral alumina column, eluting with CH2Cl2 (50 ml). The combined CH2Cl2 solution was cooled to −78°C and NaBH4 (0.19 ml of a 0.5 M solution in 2methoxyethyl ether) was added, followed by TlPF6 (0.034g, 0.097 mmol). The mixture was warmed to ambient temperature while the solvent was removed under reduced pressure. The solid was washed with pentane and ether, then extracted with CH2Cl2 to give a dark solution. The solution was passed down a 5-cm neutral alumina column, eluting with CH2Cl2 (50 ml). The solvent was removed under reduced pressure and the solid was dried, then crystallized twice from CH2Cl2 –ether to give colorless crystals. Due to incor-
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poration of ether into the crystalline lattice, the crystals were dissolved in CH2Cl2 and the solvent was rapidly removed to leave the product as a colorless solid (0.067 g, 54%). Anal. Calc. for C64H59F6P5Pd2: C, 58.68; H, 4.51. Found: C, 58.39; H, 4.62%. 1H NMR (CDCl3): d − 9.16 (q, 1H, 2J(PH) = 15 Hz, m-H); 1.87 (s, 6H, CH3); 4.09 (m, 4H, PCH2P); 6.17 (d, 4H, 3J(HH)= 8 Hz, C6H4Me); 6.33 (d, 4H, 3J(HH) = 8 Hz, C6H4Me); 7.1 – 7.4 (m, 40H, PPh2). 31P{1H} NMR: d 15.6 (s). Following a separate experiment, in which NaBH3CN was used instead of NaBH4, slow evaporation of a CH2Cl2 –pentane solution of the product at − 40°C gave [Pd2(C6H4Me-4)2(m-H)(m-dppm)2]BH3CN as orange plates.
3.2. Preparation of [Pd2Ph2(m-H)(m-dppm)2]PF6 (1b) The phenyl derivative was prepared similarly, and isolated as a gray solid in 80% yield. 1H NMR (CDCl3): d − 9.05 (q, 1H, 2J(PH) =15 Hz, m-H); 4.09 (m, 4H, PCH2P); 6.3–6.6 (m, 10H, PdPh); 7.2 – 7.9 (m, 40H, PPh2). 31P{1H} NMR: d 16.9 (s).
3.3. Preparation of [Pd2Me2(m-H)(m-dppm)2]PF6 (1c) This complex was prepared analogously and obtained as a gray solid in 74% yield. 1H NMR (CDCl3): d −7.55 (q, 1H, 2J(PH) = 16 Hz, m-H); 0.07 (s, 6H, CH3); 4.55 (m, 4H, PCH2P); 7.2 – 7.9 (m, 40H, PPh2). 31 P{1H} NMR: d 23.4 (s).
3.4. Preparation of [Pd2Et2(m-H)(m-dppm)2]PF6 (1d) The ethyl complex was prepared similarly and isolated as a gray solid in 54% yield. Anal. Calc. for C54H55F6P5Pd2: C, 54.69; H, 4.64. Found: C, 54.16; H, 4.65%. 1H NMR (CDCl3): d −7.79 (q, 1H, 2J(PH)= 16 Hz, m-H; − 0.07 (t, 6H, 3J(HH) = 7 Hz, CH2CH3); 1.05 (quartet, 4H, 3J(HH) = 7 Hz, CH2CH3); 4.50 (m, 4H, PCH2P); 7.2–7.9 (m, 40H, PPh2). 31P{1H} NMR: dP 23.9 (s).
3.5. Preparation of [Pd2(n-Bu)2(m-H)(m-dppm)2]PF6 (1e) This complex was prepared by the above method and was obtained as a gray solid in 45% yield. Anal. Calc. for C54H55F6P5Pd2: C, 56.10; H, 5.08. Found: C, 56.61; H, 5.07%. 1H NMR (CDCl3): d −7.68 (q, 1H, 2 J(PH)=16 Hz, m-H); −0.26 (t, 6H, 3J(HH) = 7 Hz, CH3); 0.09 (m, 8H, CH2CH2CH3); 0.95 (m, 4H, PdCH2); 4.05 (m, 4H, PCH2P); 7.2 – 7.9 (m, 40H, PPh2). 31 P{1H} NMR: d 22.5 (s).
3.6. Preparation of [Pd2(COMe)2(m-H)(m-dppm)2]PF6 (1f) Tetramethyltin (0.042 ml, 0.31 mmol) was introduced to a CH2Cl2 suspension (30 ml) of [Pd2Cl2(m-Cl)2(AsPh3)2] (0.10 g, 0.10 mmol). The mixture was allowed to stir for 3 h, CO was bubbled through it for a further 1 h, then dppm (0.079 g, 0.21 mmol), methanol (1 ml) and TlPF6 (0.072 g, 0.21 mmol) were added. The solvents were removed, the residue was washed with ether and pentane, then redissolved in CH2Cl2 and passed through a short column of neutral alumina, eluting with CH2Cl2 (30 ml). The resulting solution was cooled to −78°C and NaBH4 (0.21 ml of a 0.5 M solution in 2-methoxyethyl ether) was added by syringe, followed by TlPF6 (0.072 g, 0.21 mmol). The solvents were removed under reduced pressure while the flask was gradually warmed to ambient temperature, and the resulting dark solid was washed with hexane and ether. Extraction with CH2Cl2 (30 ml) gave a dark solution, which was passed through a neutral alumina column, eluting with CH2Cl2. The resulting pale-yellow solution was evaporated to dryness, and the crude product was crystallized twice from CH2Cl2 –ether. The crystals were redissolved in CH2Cl2 and the solvent was rapidly removed to leave a brown solid (0.079 g, 63%). Anal. Calc. for C54H51F6O2P5Pd2: C, 53.43; H, 4.21. Found: C, 53.35; H, 4.37%. 1H NMR (CDCl3): dH − 10.24 (q, 1H, 2J(PH)= 18 Hz, m-H); 1.10 (s, 6H, COCH3); 4.02 (m, 4H, PCH2P); 7.2–7.5 (m, 40H, PPh2). 31P{1H} NMR: dP 12.2 (s).
3.7. Preparation of [Pd2(COEt)2(m-H)(m-dppm)2]PF6 (1g) This complex was prepared by the above method and was obtained as a brown solid in 45% yield. Anal. Calc. for C56H55F6O2P5Pd2: C, 54.16; H, 4.43. Found: C, 53.76; H, 4.39%. 1H NMR (CDCl3): dH –9.99 (q, 1H, 2 J(PH)= 18 Hz, m-H); 0.01 (t, 6H, 3J(HH)=7 Hz, CH2CH3); 1.64 (quartet, 4H, COCH2CH3); 3.94 (m, 4H, PCH2P); 7.2–7.6 (m, 40H, PPh2). 31P{1H} NMR: dP 12.5 (s).
3.8. Preparation of [Pd2(COBn)2(m-H)(m-dppm)2]PF6 (1h) This complex was prepared by the above method and was obtained as a brown solid in 61% yield. 1H NMR (CDCl3): dH –10.10 (q, 1H, 2J(PH)= 18 Hz, m-H); 3.02 (s, 4H, COCH2Ph); 4.02 (m, 4H, PCH2P); 5.79 (d, 4H, 3J(HH)= 8 Hz, C6H5-2,6); 6.85 (t, 4H, 3J(HH)=8 Hz, C6H5 -3,5); 6.91 (t, 2H, 3J(HH)= 8 Hz, C6H5 -4); 7.2-7.6 (m, 40H, PPh2). 31P{1H} NMR: dP 12.3 (s).
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3.9. Preparation of [PdPt(C6H4Me-4)2 (m-H)(m-dppm)2]PF6 (2a) A stirred CH2Cl2 solution (30 ml) of [PdPtCl2(mdppm)2] (0.10 g, 0.088 mmol) was cooled to − 78°C and 4-tolylmagnesium bromide (1.0 ml of a 1.0 M ether solution) was introduced. The solution darkened and was stirred for 14 h. Methanol (1 ml), CBr4 (0.10 g, 0.30 mmol), and TlPF6 (0.031 g, 0.089 mmol) were added and the flask was allowed to warm to ambient temperature while the solvents were removed under reduced pressure. After washing with ether and hexane, the solid residue was extracted with CH2Cl2 and passed through a short column of neutral alumina, eluting with CH2Cl2 (50 ml). The resulting solution was again cooled to − 78°C and NaBH4 (0.18 ml of a 0.5 M solution in 2-methoxyethyl ether) was added by syringe, followed by TlPF6 (0.031 g, 0.089 mmol). The solvent was removed under reduced pressure while the flask was gradually warmed to ambient temperature, and the resulting dark solid was washed with pentane and ether. Extraction with CH2Cl2 gave a dark solution, which was passed through a neutral alumina column, eluting with CH2Cl2. The resulting pale-yellow solution was evaporated to dryness, and the crude product was crystallized twice from CH2Cl2 – ether. The crystals were re-dissolved in CH2Cl2 and the solvent was rapidly removed to leave a brown solid (0.075 g, 57%). Anal. Calc. for C64H59F6P5PdPt: C, 54.96; H, 4.23. Found: C, 54.96; H, 4.24%. 1H NMR (CDCl3): d − 8.97 (q, 1H, 2 J(PH)=11 Hz, 1J(PtH) =540 Hz, m-H); 1.85 (s, 6H, CH3); 4.34 (m, 4H, 3J(PtH) =38 Hz, PCH2P); 6.1–6.4 (m, 8H, C6H4Me); 7.2 – 7.8 (m, 40H, PPh2). 31P{1H} NMR: d 13.5 (m, 1J(PtP) =2955 Hz). Slow evaporation of a CHCl3 –Et2O solution gave the complex as colorless needles.
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0.35 mmol) was added dropwise, followed by TlPF6 (0.12 g, 0.35 mmol). The solvent was removed under reduced pressure and, after washing with ether and pentane, the residue was extracted with CH2Cl2 and filtered. The yellow solution was passed through a 5-cm neutral alumina column, eluting with CH2Cl2, then cooled to − 78°C. NaBH4 (0.70 ml of a 0.5 M solution in 2-methoxyethyl ether) was added, followed by TlPF6 (0.12 g, 0.35 mmol), then the solvent was removed under reduced pressure while the flask was allowed to warm to ambient temperature. After washing with ether and pentane, extraction with CH2Cl2 produced an orange solution, which was passed through a neutral alumina column, eluting with CH2Cl2 (50 ml). The solvent was removed and the product was crystallized twice from CH2Cl2 –ether. The crystals were re-dissolved in CH2Cl2 and the solvent was rapidly removed to give an orange solid (0.18 g, 42%). Anal. Calc. for C60H59F6P5Pd2: C, 57.10; H, 4.68. Found: C, 56.89; H, 4.70%. 1H NMR (CDCl3): d −7.87 (q, 1H, 2J(PH)= 15 Hz, m-H); 0.01 (t, 3J(PH)= 6 Hz, PdCH3); 1.84 (s, 3H, 4-CH3); 1.91 (s, 6H, 2,6-CH3); 4.01 (br s, 4H, PCH2P); 5.94 (s, 4H, C6H2Me3); 7.0–7.8 (m, 40H, PPh2). 31P{1H} NMR: d 20.9 (m, 2P, P2PdMe); 16.1 (m, 2P, P2PdMes).
3.12. Preparation of [Pd2(C6H2Me3 -2,4,6)Et(m-H)(m-dppm)2]PF6 (3b)
The phenyl analogue was prepared analogously, and the product was obtained as a pale-yellow solid (0.076 g, 64%). 1H NMR (acetone-d6): d − 9.04 (q, 1H, 2 J(PH)=11 Hz, 1J(PtH) = 535 Hz, m-H); 4.40 (m, 4H, 3 J(PtH)=43 Hz, PCH2P); 7.2 – 7.8 (m, 50H, C6H5). 31 P{1H} NMR: d 15.2 (m, 1J(PtP) =2853 Hz).
The complex was prepared as above starting from [PdCl2(cod)] (0.10 g, 0.35 mmol) and 2-mesitylmagnesium bromide (0.53 ml of a 1.0 M ether solution). A CH2Cl2 solution of [Pd2Et2(m-Cl)2(AsPh3)2] (prepared from [Pd2(m-Cl)2Cl2(AsPh3)2] (0.17 g, 0.18 mmol) and Et4Sn (0.10 ml, 0.52 mmol) in CH2Cl2 (20 ml)) was added dropwise in the second step. After reaction with NaBH4 and TlPF6, the product was obtained as an orange solid (0.20 g, 45%). 1H NMR (CDCl3): d −7.95 (q, 1H, 2J(PH)= 16 Hz, m-H); − 0.01 (m, 2H, PdCH2); 1.10 (m, 3H, CH3); 1.86 (s, 3H, 4-CH3); 2.01 (s, 6H, 2,6-CH3); 3.99 (br s, 4H, PCH2P); 5.95 (s, 2H, C6H2Me3); 7.0–7.8 (m, 40H, PPh2). 31P{1H} NMR: d 20.5 (m, 2P, P2 PdEt); 16.0 (m, 2P, P2 PdMes). Slow evaporation of a CH2Cl2 –Et2O solution resulted in crystallization of the complex as orange cuboids.
3.11. Preparation of [Pd2(C6H2Me3 -2,4,6)Me(m-H)(m-dppm)2]PF6 (3a)
3.13. Preparation of [Pd2(C6H2Me3 -2,4,6)Ph(m-H)(m-dppm)2]PF6 (3c)
A stirred CH2Cl2 solution (30 ml) of [PdCl2(cod)] (0.10 g, 0.35 mmol) was cooled to −78°C and 2mesitylmagnesium bromide (0.53 ml of a 1.0 M solution in ether) was added by syringe. After 30 min, methanol (1.0 ml) was added along with dppm (0.27 g, 0.70 mmol). The solution was stirred for 14 h, then a CH2Cl2 solution (20 ml) of [PdClMe(cod)] (0.093 g,
The complex was prepared from [PdCl2(cod)] (0.10 g, 0.35 mmol) and 2-mesitylmagnesium bromide (0.53 ml of a 1.0 M solution in ether). A CH2Cl2 solution (20 ml) of [Pd2Ph2(m-Cl)2(AsPh3)2] (0.18 g, 0.18 mmol) was added dropwise in the second step. After reaction with NaBH4 and TlPF6, the product was isolated as an orange solid (0.28 g, 59%). Anal. Calc. for
3.10. Preparation of [PdPtPh2(m-H)(m-dppm)2]PF6 (2b)
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C65H62F6P5Pd2: C, 58.92; H, 4.68. Found: C, 58.69; H, 4.77%. 1H NMR (CDCl3): d −8.66 (q, 1H, 2J(PH)= 15 Hz, m-H); 1.87 (s, 3H, 4-CH3); 2.01 (s, 6H, 2,6-CH3); 4.05 (s, 4H, PCH2P); 5.94 (s, 2H, C6H2Me3); 6.3–6.6 (m, 5H, PdPh); 7.0 – 7.8 (m, 40H, PPh2). 31P{1H} NMR: d 15.9 (m, 2P, P2PdPh); 14.2 (m, 2P, P2PdMes). Slow evaporation of a CH2Cl2 – C6H6 – Et2O solution gave the complex as pale-yellow crystals.
3.14. X-ray structure determinations For complexes 1a, 2a, 3b and 3c, preliminary examination and data collection were performed using a Siemens SMART CCD detector system single-crystal X-ray diffractometer equipped with a sealed tube X-ray source (50 kV × 40 mA) using graphite-monochromated Mo Ka radiation (l =0.71073 A, ). Preliminary unit cell constants were determined with a set of 45 narrow frame (0.3° in 6) scans. The double pass method of scanning was used to exclude any noise. The collected frames were integrated using an orientation matrix determined from the narrow frame scans. The SMART software package [24] was used for data collection and SAINT [24] was used for frame integration. Final cell constants were determined by a global refinement of xyz centroids of 8192 reflections. An empirical absorption correction was applied using SADABS [25]. Structure solution and refinement were carried out using the SHELXTL-PLUS (5.03) software package [26].
For complex 4 preliminary examination and data collection were performed using a Siemens R3 singlecrystal X-ray diffractometer using graphite-monochromated Mo Ka radiation (l= 0.71073 A, ). Autoindexing of 10 centered reflections from the rotation photograph resulted in a triclinic cell. Axial photographs were taken to confirm the cell lengths. Final cell constants and orientation matrix for data collection were calculated by least-squares refinement of the setting angles for 30 reflections (32°B 2u B 35°). Intensity data were collected using v/2u scans with variable scan speed. Three representative reflections measured every 50 reflections showed B 12% variation during data collection. Data reduction was carried out by XDISK [24]. In each case, the structure was solved by Patterson methods and refined successfully in the space group given in Table 7. Full-matrix least-squares refinement was carried out by minimizing Sw(F o2 − F c2)2. The non-hydrogen atoms were refined anisotropically to convergence. The hydrogen atoms were treated using appropriate riding models (AFIX m3). Crystal data and structure refinement parameters are given in Table 7. The mesityl compounds are not disordered, but the three other compounds exhibit positional disorder. Compounds 1a and 4 crystallize in the triclinic space group P1( . In 1a the cation is not disordered, as would be expected since the metal and ligands are identical in both halves of the A-frame. The cation and the BH3CN− anion are located around an inversion center, so 50% of the A-frame is unique and there are two
Table 7 Crystallographic data for complexes 1a, 2a, 3b, 3c and 4 Complex
1a
2a
3b
3c
4
Crystal system Space group Unit cell dimensions a (A, ) b (A, ) c (A, ) a (°) b (°) g (°) V (A, 3) Z Dcalc (Mg m−3) Temperature (K) Absorbtion coefficient (mm−1) u Range (°) Reflections collected Independent reflections Observed reflections Absorption correction No. parameters refined R(F), Rw(F 2) (F 2\2.0s(F 2)) R(F), Rw(F 2) (all data) Goodness of fit Largest difference peak, hole (e A, −3)
triclinic P1(
monoclinic P21/n
monoclinic C2/c
monoclinic P21/n
triclinic P1(
11.5028(1) 12.4083(1) 12.4609(2) 106.587(1) 93.100(1) 116.809(1) 1486.16(3) 1 1.346 223(2) 0.752 1.75 to 28.00 44 293 7139 7139 empirical 355 0.0440, 0.1207 0.0689, 0.1350 1.025 1.051, −1.055
14.6934(2) 26.0200(1) 16.9169(1) 90 96.59(1) 90 6424.97(10) 4 1.568 223(2) 2.760 1.44 to 25.00 73 690 11 294 11 225 empirical 754 0.0635, 0.1391 0.1368, 0.1742 1.068 1.454, −1.389
43.7235(6) 12.1038(2) 23.7965(1) 90 115.095(1) 90 11 404.8(2) 8 1.486 223(2) 0.829 1.73 to 25.00 60 162 10 058 10 058 empirical 671 0.0601, 0.1130 0.1688, 0.1488 0.947 0.828, −0.766
12.2426(2) 22.8016(3) 26.5958(4) 90 101.707(1) 90 7269.8(2) 4 1.388 218(2) 0.663 1.19 to 25.00 132 945 12 807 12 807 none 818 0.0552, 0.1239 0.1166, 0.1551 1.001 0.676, −0.624
10.853(2) 12.080(2) 12.179(2) 84.570(10) 72.840(10) 87.990(10) 1518.8(5) 1 1.639 298(2) 3.046 1.69 to 27.56 7388 7017 7017 empirical 340 0.0644, 0.1285 0.1169, 0.1542 1.047 1.075, −0.963
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unique disordered BH3CN− fragments. The site C1% of the first BH3CN− fragment is coincident with B1% for the second fragment. All atoms of the anion were refined with 25% occupancy factors. In 4 the cation is disordered. The molecule is centered around the inversion center making 50% of the molecule unique. Therefore, the Pt and Pd sites and the ligands attached to the metals (Et and Me) are disordered. The disorder was modeled as 50% occupancy for the metals and the Et/Me fragments. The mixed metal compound 2a crystallizes in the monoclinic space group P21/n. The metal positions are disordered and were refined with 50% occupancy at both sites.
4. Supplementary material Atomic coordinates and anisotropic displacement coefficients for the non-hydrogen atoms, positional and isotropic displacement coefficients for the hydrogen atoms, complete lists of bond distances and angles, and calculated and observed structure factors are available form the author. Crystallographic data for the structural analysis has been deposited with the Cambridge Crystallographic Data Centre, CCDC 134200 for compound 1a, 139844 for compound 4, 139845 for compound 2a, 139846 for compound 3b and 139847 for compound 3c. Copies of this information may be obtained free of charge from: The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: + 441223-336-033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk).
Acknowledgements Thanks are expressed to the National Science Foundation (grant no. CHE-9508228) for support of this work, to Mallinckrodt Inc. for a fellowship (to RASJ), and to the National Science Foundation (grant nos. CHE-9318696 and 9309690), the US Department of Energy (grant no. DE-FG02-92CH10499) and the University of Missouri Research Board for instrumentation grants.
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References [1] B. Chaudret, B. Delavaux, R. Poilblanc, Coord. Chem. Rev. 86 (1988) 191. [2] R.J. Puddephatt, L. Manojlovic-Muir, K.W. Muir, Polyhedron 9 (1990) 2767. [3] G.K. Anderson, Adv. Organomet. Chem. 35 (1993) 1. [4] J.R. Fisher, A.J. Mills, S. Sumner, M.P. Brown, M.A. Thomson, R.J. Puddephatt, A.A. Frew, L. Manojlovic-Muir, K.W. Muir, Organometallics 1 (1982) 1421. [5] M.P. Brown, R.J. Puddephatt, M. Rashidi, K.R. Seddon, J. Chem. Soc., Dalton Trans. (1978) 516. [6] A.A. Frew, R.H. Hill, L. Manojlovic-Muir, K.W. Muir, R.J. Puddephatt, J. Chem. Soc., Chem. Commun. (1982) 198. [7] K.A. Azam, R.J. Puddephatt, Organometallics 2 (1983) 1396. [8] M.P. Brown, S.J. Cooper, A.A. Frew, L. Manojlovic-Muir, K.W. Muir, R.J. Puddephatt, M.A. Thomson, J. Chem. Soc., Dalton Trans. (1982) 299. [9] K.A. Azam, M.P. Brown, S.J. Cooper, R.J. Puddephatt, Organometallics 1 (1982) 1183. [10] C. Xu, G.K. Anderson, Organometallics 13 (1994) 3981. [11] C. Xu, G.K. Anderson, Organometallics 15 (1996) 1760. [12] S.J. Young, B. Kellenberger, J.H. Reibenspies, S.E. Himmel, M. Manning, O.P. Anderson, J.K. Stille, J. Am. Chem. Soc. 110 (1988) 5744. [13] R.A. Stockland Jr., G.K. Anderson, N.P. Rath, Inorg. Chim. Acta 259 (1997) 173. [14] R.A. Stockland Jr., G.K. Anderson, N.P. Rath, J. Am. Chem. Soc. 121 (1999) 7945. [15] R.A. Stockland Jr., G.K. Anderson, N.P. Rath, Organometallics 16 (1997) 5096. [16] P.G. Pringle, B.L. Shaw, J. Chem. Soc., Dalton Trans. (1983) 889. [17] C. Xu, G.K. Anderson, Inorg. Chim. Acta 228 (1995) 73. [18] C. Xu, G.K. Anderson, L. Brammer, J. Braddock-Wilking, N.P. Rath, Organometallics 15 (1996) 3972. [19] C. Xu, G.K. Anderson, N.P. Rath, Inorg. Chim. Acta 265 (1997) 241. [20] R.J. Puddephatt, K.A. Azam, R.H. Hill, M.P. Brown, C.D. Nelson, R.P. Moulding, K.R. Seddon, M.C. Grossel, J. Am. Chem. Soc. 105 (1983) 5642. [21] (a) M.M. Olmstead, L.S. Benner, H. Hope, A.L. Balch, Inorg. Chim. Acta 32 (1979) 193. (b) P. Espinet, J. Fornies, C. Fortuno, G. Hidalgo, F. Martinez, M. Tomas, A.J. Welch, J. Organomet. Chem. 317 (1986) 105. (c) T.E. Krafft, C.I. Hejna, J.S. Smith, Inorg. Chem. 29 (1990) 2682. [22] J. Chatt, L.M. Vallarino, L.M. Venanzi, J. Chem. Soc. (1957) 3413. [23] C.T. Hunt, A.L. Balch, Inorg. Chem. 21 (1982) 1641. [24] Siemens Analytical X-Ray Division, Madison, WI, USA. [25] R.H. Blessing, Acta Crystallogr., Sect. A 51 (1995) 33. [26] G.M. Sheldrick, Siemens Analytical X-Ray Division, Madison, WI, 1995.
Synthesis and structures of hydride-bridged palladium A-frame complexes Robert A. Stockland Jr., Gordon K. Anderson *, Nigam P. Rath Department of Chemistry, Uni6ersity of Missouri-St. Louis, 8001 Natural Bridge Road, St. Louis, MO 63121, USA Received 22 September 1999; accepted 7 December 1999
Abstract A series of hydride-bridged palladium A-frame complexes [Pd2R2(m-H)(m-dppm)2]PF6 has been prepared by reaction of [Pd2Cl2(m-dppm)2] with 2 equiv. of a Grignard reagent, followed by addition of CBr4, NaBH4 and TlPF6. The mixed palladium–platinum species [PdPtR2(m-H)(m-dppm)2]PF6 were generated analogously from [PdPtCl2(m-dppm)2], whereas the unsymmetrical dipalladium derivatives [Pd2(Mes)R(m-H)(m-dppm)2]PF6 were produced from the reaction of [Pd(Mes)(dppm)2]X with [Pd2R2(m-Cl)2(AsPh3)2], followed by treatment with NaBH4. The complexes were characterized by elemental analysis, 1H and 31 P NMR spectroscopy. The solid-state structures of [Pd2(C6H4Me-4)2(m-H)(m-dppm)2]BH3CN (1a) (obtained as its BH3CN− salt when NaBH3CN was used instead of NaBH4), [PdPt(C6H4Me-4)2(m-H)(m-dppm)2]PF6 (2a), [Pd2(Mes)Et(m-H)(m-dppm)2]PF6 (3b), [Pd2(Mes)Ph(m-H)(m-dppm)2]PF6 (3c) and [EtPt(m-H)(m-dppm)2PdMe]PF6 (4) have been determined by X-ray crystallography. 3c adopts an elongated boat conformation in the solid state, whereas the others exist in the chair form. The unsymmetrical cations 2a and 4 containing smaller organic substituents are disordered in the solid state, whereas the mesityl-containing derivatives 3b and 3c are not. © 2000 Elsevier Science S.A. All rights reserved. Keywords: Crystal structures; Hydride-bridged complexes; Palladium complexes
1. Introduction The chemistry of transition metal complexes bridged by dppm or related ligands is now extensive [1–3]. Dimeric and trimeric palladium and platinum species, in particular, are numerous. The dimeric complexes typically contain two bridging diphosphines, and include ‘side-by-side’ derivatives containing a metal– metal bond, trans,trans and cis,cis complexes with no other bridging groups, and A-frames in which there is one additional bridging group. Although A-frame complexes of these metals are well known, those containing a hydride as the additional bridging moiety are relatively few, and only two have been characterized crystallographically (vide infra). The platinum trihydride [Pt2H2(m-H)(m-dppm)2]+ was generated by Puddephatt and co-workers by NaBH4 * Corresponding author. Tel.: + 1-314-516 5311; fax: + 1-314-516 5342. E-mail address: [email protected] (G.K. Anderson)
reduction of [PtCl2(dppm)] [4–6], and the related complexes [Pt2HMe(m-H)(m-dppm)2]+ and [Pt2R2(m-H)(mdppm)2]+ (R=Me, Et) have also been prepared [7–9]. We have shown that unsymmetrical hydride-bridged platinum complexes may also be prepared by reaction of [PtR(dppm-PP)(dppm-P)]+ with [PtClR%(cod)], followed by reduction to give [RPt(m-H)(m-dppm)2PtR%]+, and this methodology may be extended to mixed platinum–palladium species [10,11]. The first hydridebridged palladium A-frame was described by Stille and co-workers, formed by the reaction of [Pd2Cl2(mdppm)2] with Me3Al, followed by NaBPh4 and ethanol [12], although they reported it to be thermally unstable. We have reported that the chloride-bridged palladium A-frames [Pd2R2(m-Cl)(m-dppm)2]+ may be reduced with NaBH4 or NaBH3CN to generate the corresponding hydride-bridged complexes [13]. We found these to be quite stable at ambient temperature, although they do undergo elimination reactions at elevated temperatures [14].
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 9 9 ) 0 0 6 0 6 - 4
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The platinum complex [Pt2Me2(m-H)(m-dppm)2]PF6 was characterized by X-ray crystallography, although the bridging hydride was not located [8]. We reported the solid-state structure of the ethylpalladium derivative [Pd2Et2(m-H)(m-dppm)2]PF6, in which the ethyl groups and bridging hydride were disordered over two positions [13]. These represent the only two structures of hydride-bridged A-frame complexes of the Group 10 metals reported to date. In this paper we report the synthesis of palladium and mixed metal A-frame complexes, and the solid-state structures of five hydridebridged derivatives. 2. Results and discussion We have shown that hydride-bridged organopalladium A-frames are generally available by replacement of a bridging halide using NaBH4. The halide-bridged derivatives [Pd2R2(m-X)(m-dppm)2]+ may be prepared from reactions of [PdClR(cod)] (R= Me, Bn) or [Pd2R2(m-Cl)2(AsPh3)2] (R= Me, Et, Bu, Ph) with dppm [13], and we have extended this to the acylpalladium species [Pd2(COR)2(m-X)(m-dppm)2]+ (R =Me, Et, Bn) by reacting the chloride-bridged arsine dimers with CO prior to the introduction of dppm. Alternatively, halide-bridged compounds may be obtained by treatment of [PdX2(dppm)] with a Grignard reagent (R= Me, Et, Bu, CH2SiMe3, Bn, Mes) [15]. These methods are not generally applicable to complexes with aryl substituents, however. We have now developed a more versatile approach that may be used with aryls, as well as with a range of alkyl groups, starting from the palladium(I) precursor [Pd2Cl2(m-dppm)2], as outlined in Scheme 1. Synthesis of the halide-bridged species by this method will be described in detail elsewhere, but a brief synopsis will be provided here.
Reaction of [Pd2Cl2(m-dppm)2] with an excess of the appropriate Grignard reagent in CH2Cl2 solution at low temperature generated [Pd2R2(m-dppm)2] which, on treatment with CBr4, resulted in nearly quantitative formation of the bromide-bridged A-frame. Addition of a solution of NaBH4 at low temperature provided quantitative conversion to the hydride-bridged species, 1a–e, which may also be isolated conveniently as their PF6− salts. The acyl species [Pd2(COR)2(m-H)(mdppm)2]PF6 (R=Me, Et, Bn), 1f–h, were generated by reaction of [Pd2R2(m-Cl)2(AsPh3)2] with CO and dppm, followed by NaBH4. The mixed metal complexes 2a,b could be obtained starting from [PdPtCl2(m-dppm)2] [16] according to the procedure outlined in Scheme 2. The above systems permit only the synthesis of complexes in which the two terminal organic groups are identical. We had previously prepared a range of platinum-containing dppm-bridged species using the [PtR(dppm-PP)(dppm-P)]+ precursors [10,11,17–19], obtained by treating [PtClR(cod)] with 2 equiv. of dppm. With palladium, however, dimerization of the [PdClR(dppm)] intermediate is much faster than coordination of the second dppm ligand, except with the very bulky mesityl system. In this case, reactions of the [Pd(Mes)(dppm-PP)(dppm-P)]+ cation with [Pd2R2(mCl)2(AsPh3)2] (R= Me, Et, Ph) at low temperature gave the unsymmetrical A-frames [Pd2(Mes)R(m-X)(mdppm)2]+ in excellent yield as mixtures of chloride- and bromide-bridged species. These were not isolated, but further reaction with NaBH4 gave the hydride-bridged derivatives, 3a–c (Scheme 3), which were again isolated as their PF6− salts. The hydride-bridged A-frame complexes were isolated as colorless to light-brown powders. In the solid state they could be stored for several weeks without discoloration in the absence of light; if kept below
Scheme 1.
Scheme 2.
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Scheme 3.
− 40°C no signs of decomposition could be observed over more extended time periods. Dichloromethane solutions of the complexes could be stored below − 40°C for several weeks without significant discoloration, but decomposition occurred over longer periods. Incorporation of platinum in 2, or the bulky mesityl group in 3, affords greater thermal stability to the hydride-bridged complexes. The 31P{1H} NMR spectra of the symmetrical complexes 1 each exhibit a single resonance, the alkyl complexes appearing at slightly higher frequencies than the aryls, and shifted by approximately 5 ppm to high frequency of their halide analogues. The unsymmetrical palladium species 3 give rise to two multiplets due to the presence of two pairs of equivalent P atoms. The chemical shifts of the P atoms attached to palladium and platinum in 2a,b are coincidentally identical, so a single resonance is observed with 195Pt satellites of approximately half the usual intensity. The 1H NMR spectra of the hydride complexes contain the expected resonances due to the terminal organic fragments. In each case the CH2 groups of the dppm ligands give rise to one broad multiplet in the range 3.9 – 4.7 ppm, the methylene hydrogens being equivalent due to rapid inversion of the A-frame structure [20]. The bridging hydride appears as a quintet in each case, due to coupling to the four P atoms (in the unsymmetrical compounds the two 2J(P,H) values are identical), between − 7.5 and − 10.3 ppm. The position of the hydride resonance depends significantly on the nature of the terminal organic groups, being around − 9.1 ppm in the aryl derivatives 1a,b, between − 7.5 and − 7.8 ppm in the alkyl complexes 1c – e, and between − 10.0 and −10.3 ppm in the acyls 1f –h. The introduction of one platinum for palladium in 2a,b has little effect on the chemical shift of the hydride. In the unsymmetrical palladium complexes, the introduction of a mesityl group causes the hydride to be slightly more shielded in 3a,b compared to 1c,d, whereas in 3c it is less shielded than in the corresponding diphenyl complex 1b. The mesityl-containing compounds 3 each exhibit two resonances in a 2:1 ratio, due to the two ortho and one para methyls. Thus, the two ortho methyl groups are equivalent. This could arise due to free rotation about the Pd-mesityl bond, or because the two faces of the Pd2P4 core are equivalent on the NMR time
scale. The latter is more likely because rotation about the Pd-mesityl bond is slow in the bromide-bridged complex [Pd2(Mes)2(m-Br)(m-dppm)2]PF6 [15]. We reported previously the solid-state structure of [Pd2Et2(m-H)(m-dppm)2]PF6 (1d) [13], the first example of a hydride-bridged palladium A-frame complex to be characterized by X-ray crystallography. In the cation, the ethyl groups and bridging hydride were disordered over two sites, and the eight-membered Pd2P4C2 ring adopted an elongated chair conformation. Here we report the structures of a further five hydride-bridged A-frames, namely (1a) (as its BH3CN− salt), 2a, 3b, 3c and [EtPt(m-H)(m-dppm)2PdMe]+ (4) [10] (as their PF6− salts). [Pd2(C6H4Me-4)2(m-H)(m-dppm)2]BH3CN(1a·BH3CN), crystallized in the P1( space group as orange plates from CH2Cl2 –pentane solution at − 40°C. Although TlPF6 was added in order to replace the counterion, incomplete conversion to the hexafluorophosphate salt took place in this case, and crystallization as the cyanoborohydride (which is disordered) occurred. The molecular structure of the cation is shown in Fig. 1, and selected bond distances and angles are presented in Table 1. The are no close contacts between the cation and BH3CN−. The cation comprises of two Pd atoms linked by two dppm ligands and a hydride, and two terminal tolyl groups. The PdPd distance is 3.0758(4) A, , indicating
Fig. 1. Projection view of the molecular structure 1a showing the atom-labeling scheme, with non-hydrogen atoms represented by 50% probability ellipsoids.
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Table 1 Selected bond distances (A, ) and angles (°) for 1a·BH3CN PdPd% PdP(2)
3.0758(4) 2.2936(7)
PdP(1) PdC(3)
2.3030(7) 2.032(3)
P(1)PdP(2) P(2)PdC(3) P(1)PdPd%
175.97(3) 90.51(8) 91.43(2)
P(1)PdC(3) C(3)PdPd% P(2)PdPd%
88.87(8) 178.41(9) 89.08(2)
Fig. 2. Projection view of the molecular structure of 2a showing the atom-labeling scheme, with non-hydrogen atoms represented by 50% probability ellipsoids. Table 2 Selected bond distances (A, ) and angles (°) for 2a PdPt PdP(2) PtP(4) PtC(34)
3.0126(7) 2.287(2) 2.291(2) 2.095(10)
PdP(1) PtP(3) PdC(3)
2.285(2) 2.292(2) 2.055(10)
P(1)PdP(2) P(1)PdC(3) P(3)PtC(34) C(3)PdPt
175.21(9) 89.0(3) 91.0(3) 170.9(3)
P(3)PtP(4) P(2)PdC(3) P(4)PtC(34) C(34)PtPd
178.28(9) 88.1(3) 88.0(3) 167.6(3)
that there is no significant metal – metal interaction. The PPdP angles approach linearity (175.97(3)°); the PdP distances are unremarkable and almost identical. The tolyl ligands lie trans to the bridging hydride, and the PdC distance is 2.032(3) A, . As found for [Pd2Et2(m-H)(m-dppm)2]+, the cation crystallizes in an eight-membered elongated chair conformation, with the dppm CH2 groups lying on opposite faces of the Pd2P4 plane. The PPdPdP torsion angles are 4.0°, indicating that the PPdP vectors are nearly parallel and the Pd2P4 unit is nearly planar (as is the case for the ethylpalladium cation [13]). The most remarkable feature of the structure is the almost perfectly linear nature of the CPdPdC unit, the CPdPd angles being 178.44(9)°. Such a linear RMHMR species has been proposed as the intermediate in the fluxional
process that equilibrates the faces of a hydride-bridged A-frame complex [20], and the present structure would represent the capturing of that intermediate in the solid state. The mixed metal complex [PdPt(C6H4Me-4)2(m-H)(mdppm)2]PF6 (2a) crystallized from CDCl3 –Et2O solution as colorless needles in the monoclinic space group P21/n. The asymmetric unit contained a CDCl3 molecule per molecule of 2a. The molecular structure of the cation is shown in Fig. 2, and selected bond lengths and angles are given in Table 2. The structure is disordered over the two metal positions, and the refinement was carried out using 50% occupancy of each metal in each of the two sites. Such disorder is perhaps unsurprising because the covalent radii of palladium and platinum are nearly identical. The cation consists of the metals connected via two dppm ligands and the bridging hydride, and two terminal tolyl moieties. The metal–metal distance of 3.0126(7) A, again suggests the lack of any significant interaction. The MP distances are unsurprising, and the PMP angles are 175.21(9) and 178.28(9)°. The cation again crystallizes in an elongated chair conformation. The CMM% angles are 170.9(3) and 167.6(3)°, and the PMMP torsion angles of 2.5 and 3.0° show that the PMP vectors are again almost parallel. Orange cuboids of [Pd2(Mes)Et(m-H)(m-dppm)2]PF6 (3b) were obtained from CH2Cl2 –Et2O solution. The compound crystallized in the space group C2/c. No solvent molecules were incorporated into the unit cell and the structure was not disordered. In fact, this represents the first unsymmetrical palladium or platinum hydride-bridged A-frame complex that is not disordered. The molecular structure of the cation is shown in Fig. 3 and selected bond distances and angles are presented in Table 3. The cation consists of two Pd
Fig. 3. Projection view of the molecular structure of 3b showing the atom-labeling scheme, with non-hydrogen atoms represented by 50% probability ellipsoids.
R.A. Stockland Jr. et al. / Inorganica Chimica Acta 300–302 (2000) 395–405 Table 3 Selected bond distances (A, ) and angles (°) for 3b Pd(1)Pd(2) Pd(1)P(2) Pd(2)P(4) Pd(2)C(3)
2.9302(8) 2.291(2) 2.278(2) 2.115(7)
Pd(1)P(1) Pd(2)P(3) Pd(1)C(5)
2.330(2) 2.324(2) 2.071(8)
P(1)Pd(1)P(2) P(2)Pd(1)C(5) P(3)Pd(2)C(3) C(5)Pd(1)Pd(2)
166.70(8) 87.8(2) 91.2(2) 147.0(2)
P(1)Pd(1)C(5) P(3)Pd(2)P(4) P(4)Pd(2)C(3) C(3)Pd(2)Pd(1)
96.3(2) 173.10(8) 85.2(2) 158.5(2)
Table 4 Selected bond distances (A, ) and angles (°) for 3c Pd(1)Pd(2) Pd(1)P(2) Pd(2)P(4) Pd(2)C(12)
2.9836(6) 2.312(2) 2.303(2) 2.030(7)
Pd(1)P(1) Pd(2)P(3) Pd(1)C(3)
2.292(2) 2.301(2) 2.052(7)
P(1)Pd(1)P(2) P(2)Pd(1)C(3) P(3)Pd(2)C(12) C(3)Pd(1)Pd(2)
178.61(6) 88.5(2) 90.1(2) 156.6(3)
P(1)Pd(1)C(3) P(3)Pd(2)P(4) P(4)Pd(2)C(12) C(12)Pd(2)Pd(1)
90.3(2) 175.39(6) 87.0(2) 165.3(2)
atoms linked by two dppm ligands and the bridging hydride, one Pd atom being ligated by the mesityl ring and the other by the ethyl group. The PdPd distance is 2.9302(8) A, , shorter than that in either of the cations described above. The cation again adopts an elongated chair conformation. The PdP bond lengths are not identical, with each Pd atom having one shorter and one longer PdP distance. The PPdPdP torsion angles are 9.1 and 10.6°, indicating that the Pd2P4 unit is more twisted than in the other hydride-bridged palladium complexes. The PdC distance is slightly shorter for the mesityl group than for ethyl. A number of features of the structure are likely results of the presence of a bulky substituent on one palladium. The mesityl ring lies almost perpendicular to the Pd2P4 unit, as previously found for the bromide-bridged complex [Pd2(Mes)2(m-Br)(m-dppm)2]PF6 [15]. The PPdP angles are 166.70(8) and 173.10(8)°, the greater deviation from linearity being at the mesitylpalladium center. The EtPdPd angle is 158.5(2)°, almost identical to that found in [Pd2Et2(m-H)(m-dppm)2]+ [13], whereas the MesPdPd angle is significantly smaller at 147.0(2)°. Although one might expect a more linear MesPdPd fragment, in which the bulky group points directly away from the second metal center, to be sterically favored, the bending of the PPdP axis and the perpendicular orientation of the mesityl ring allow it to adopt a smaller angle such that the ring lies between the dppm phenyl groups. The bridging hydride was located from the residual electron density map and successfully refined. Although too much confidence should not be placed on the position of a single hydrogen atom, the
399
refined position does reflect the unsymmetrical nature of the complex. The PdH distances are 1.53 and 1.96 A, , the shorter distance being trans to the ethyl fragment. Complex [Pd2(Mes)Ph(m-H)(m-dppm)2]PF6 (3c) was obtained as pale-yellow crystals by slow evaporation of a CH2Cl2 –C6H6 –Et2O solution. The compound crystallized in the space group P21/n, with 2.5 benzene molecules per molecule of 3c. Again, the structure was not disordered. The molecular structure of the cation is shown in Fig. 4 and selected bond distances and angles are presented in Table 4. The cation consists of two Pd atoms linked by two dppm ligands and a bridging hydride, the mesityl ring being coordinated to one Pd atom and the phenyl group to the other. The PdPd distance is 2.9836(6) A, , slightly longer than that in 3b. In contrast to all of the examples previously discussed, this cation adopts an elongated boat conformation with both dppm CH2 groups oriented on the same face of the Pd2P4 plane, and opposite the mesityl and phenyl substituents. The PdP bond lengths involving the phenylpalladium center are identical, but the mesitylpalladium center has PdP distances that differ by 0.02 A, . The PPdPdP torsion angles are 9.5 and 13.8°, indicating that the Pd2P4 unit is again significantly twisted from planarity. As in 3b, the mesityl ring lies almost perpendicular to the Pd2P4 unit. The distortion from square planar geometry at the mesitylpalladium center seen in 3b is not found here, the PPdP and PPdC angles being 178.61(6), 88.5(2) and 90.3(2)°, respectively. The MesPdPd and PhPdPd angles are 156.6(3) and 165.3(2)°, respectively, indicating that the central core of the cation is flatter than that in 3b. The structure of the mixed metal complex [EtPt(mH)(m-dppm)2PdMe]PF6 (4), prepared previously from [PtEt(dppm-PP)(dppm-P)]PF6 and [PdClMe(cod)] [10], was also determined. The compound crystallized as
Fig. 4. Projection view of the molecular structure of 3c showing the atom-labeling scheme, with non-hydrogen atoms represented by 30% probability ellipsoids.
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400
Fig. 5. Projection view of the molecular structure of 4 showing the atom-labeling scheme, with non-hydrogen atoms represented by 50% probability ellipsoids. Table 5 Selected bond distances (A, ) and angles (°) for 4 PdPt PtP(2) PdC(26%)
2.9088(10) 2.276(2) 2.20(3)
PtP(1) PtC(26)
2.299(2) 2.02(2)
P(1)PtP(2) P(2)PtC(26) P(2%)PdC(26%) C(26%)PdPt
175.95(9) 85.5(5) 88.8(5) 167.1(12)
P(1)PtC(26) P(1%)PdC(26%) C(26)PtPd
90.5(5) 87.5(5) 164.8(6)
light-orange crystals from CHCl3 solution in the space group P1( with two solvent molecules per A-frame unit. The molecular structure of the cation is shown in Fig. 5 and selected bond distances and angles are given in Table 5. Like 2a, the structure is disordered over the two metal positions, as well as their attached alkyl substituents, and refinement was performed using 50% occupancy of each alkylmetal fragment in each site. The cation crystallizes as an elongated chair, with a PdPt distance of 2.9088(10) A, , the shortest among the hydride-bridged A-frames studied. The PMP angles are close to 180°, and the CMM angles are 164.8(6)
and 167.1(12)°. The PMMP torsion angles are only 0.9°, showing that the central framework is almost perfectly planar. There are a number of noteworthy features of these hydride-bridged complexes, and some pertinent structural data are listed in Table 6. The ‘hydride’ bridge may be considered as a protonated metal–metal bond (although attempts to generate the cations by this route have met only with limited success) and, as such, involves a three-center two-electron bond. The metal– metal distances range from 2.9088(10) to 3.0759(7) A, for the hydride-bridged A-frames reported (Table 6). These are all relatively long compared with the distances found in metal–metal bonded palladium(I) species [21], but they lie at the shorter end of the range of distances found for other palladium A-frame derivatives [15]. The longest PdPd distances are found for 1a, which has an almost linear CPdPdC core, and its mixed metal analogue 2a. There is no clear dependence of PdPd distance on the bending of the central core or on the size of the terminal organic substituents. Indeed, the bulky mesityl-containing complex 3b exhibits one of the shortest distances; it also has the most bent central core and one of the two (along with 3c) significantly twisted Pd2P4 units. Another curious feature is that 3c adopts an extended boat conformation in the solid state, whereas all the other hydride-bridged derivatives are chairs. The observation of only one hydride signal and a single, broad resonance for the dppm CH2 groups in the 1H NMR spectra indicates that inversion of the A-frame, and interconversion of chair and boat conformations, is rapid on the NMR time scale. Since this fluxional process cannot be arrested even at −90°C it is impossible to determine the relative concentrations of the chair and boat conformations in solution. Thus, the isolation of one or the other may be entirely fortuitous, or it might indicate a predominance of one form in solution (although it need not be the major species in solution that begins to crystallize first). For the mesityl-containing complexes 3b and 3c, one is found as a chair and the other as a boat in the solid state, and this might lead us to speculate that both forms are present in nearly equal concentrations in solution (Fig. 6). In
Table 6 Selected structural data for the [RM(m-H)(m-dppm)2M%R%]+ cations
4 3b 3c 1d 2a 1a
R
M
M%
R%
MM% (A, )
MM%R% (°)
RMM% (°)
Ref.
Me Mes Me Mes Et 4-tol 4-tol
Pd Pd Pt Pd Pd Pd Pd
Pt Pd Pt Pd Pd Pt Pd
Et Et Me Ph Et 4-tol 4-tol
2.9086(10) 2.9302(8) 2.932(1) 2.9836(6) 2.9933(7) 3.0126(7) 3.0758(7)
165.0(5) 158.5(2) 161.794 165.3(2) 159.4(3) 167.6(3) 178.44(7)
167.9(5) 147.0(2) 169.413 156.6(3)
this this [8] this [13] this this
170.9(3)
work work work work work
R.A. Stockland Jr. et al. / Inorganica Chimica Acta 300–302 (2000) 395–405
401
Fig. 6. Views of the central cores of 3b and 3c to illustrate the elongated chair and boat conformations.
contrast, when the complex contains smaller organic groups on palladium the chair form may predominate in the crystallizing solution, and only chair conformations are found in the solid state. In the boat structure 3c each of the equatorial hydrogens of the dppm methylene groups exhibits a somewhat short distance (3.47 and 3.52 A, ) to the centroid of a dppm phenyl ring of an adjacent molecule, whereas the axial hydrogens show intramolecular CH···centroid distances of 3.83 and 3.94 A, . Each of the chair complexes has only the longer methylene CH···centroid distances (intra- and/or intermolecular) in the range 3.79–3.94 A, . In addition, complexes 2a, 3b, 3c and 4 exhibit hydrogen bonding between dppm phenyl hydrogens and the PF6− anions, with H···F distances lying in the range 2.37 – 2.81 A, . There are also relatively short H···F contacts involving the C6H6 solvent in 3c (2.34 and 2.49 A, ) and the CHCl3 molecule in 4 (2.35 and 2.47 A, ). There is no obvious hydrogen bonding in the structure of 1a. As pointed out above, the mesityl-containing Aframes are the only unsymmetrical hydride-bridged derivatives that are not disordered. Consideration of space-filling models of the complexes reveals that the shape of the cation is dominated by the dppm phenyl groups; between the phenyls are two cavities that may be occupied by the metals and the terminal organic moieties. Palladium and platinum are almost identical in size, so incorporation of one or the other will have a minimal effect on the periphery of the cation. When two smaller organic groups are involved (in 4 for example) neither cavity is filled completely and the ‘ends’ of the A-frame appear to be similar. In 3b and 3c the bulky mesityl group fills one of the cavities, whereas the ethyl or phenyl group does not, and the two ‘ends’ of the structure are readily distinguishable. Recognition of this difference during the crystallization process should lead to an ordered structure, as is found to be the case. Where the two ends appear similar, crystallization in either orientation can occur, and hence a disordered structure may be obtained.
3. Experimental All reactions were carried out under an argon atmosphere. [PdCl2(cod)], [Pd2Cl2(m-dppm)2] and [PdPtCl2(mdppm)2] were prepared by reported methods [16,22,23]. Grignard reagents were purchased from Aldrich. 1H and 31P{1H} NMR spectra were recorded on a Varian Unity plus 300 or Bruker ARX-500 spectrometer. Chemical shifts are relative to the residual solvent resonance or external H3PO4 respectively, positive shifts representing deshielding. The following abbreviations are used: s = singlet, t =triplet, q = quintet, m =multiplet. Microanalyses were performed by Atlantic Microlab, Norcross, GA.
3.1. Preparation of [Pd2(C6H4Me-4)2(m-H)(m-dppm)2]PF6 (1a) A stirred CH2Cl2 solution (30 ml) of [Pd2Cl2(mdppm)2] (0.10 g, 0.095 mmol) was cooled to −78°C, and 4-tolylmagnesium bromide (1.0 ml of a 1.0 M solution in ether) was added. The solution turned an intense dark-red color, and was stirred for 5 h. Methanol (1 ml), CBr4 (0.10 g, 0.30 mmol), and TlPF6 (0.034 g, 0.097 mmol) were added and the flask was allowed to warm to ambient temperature while the solvents were removed under reduced pressure. After washing with ether and hexane, the solid residue was extracted with CH2Cl2 and passed through a 5-cm neutral alumina column, eluting with CH2Cl2 (50 ml). The combined CH2Cl2 solution was cooled to −78°C and NaBH4 (0.19 ml of a 0.5 M solution in 2methoxyethyl ether) was added, followed by TlPF6 (0.034g, 0.097 mmol). The mixture was warmed to ambient temperature while the solvent was removed under reduced pressure. The solid was washed with pentane and ether, then extracted with CH2Cl2 to give a dark solution. The solution was passed down a 5-cm neutral alumina column, eluting with CH2Cl2 (50 ml). The solvent was removed under reduced pressure and the solid was dried, then crystallized twice from CH2Cl2 –ether to give colorless crystals. Due to incor-
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poration of ether into the crystalline lattice, the crystals were dissolved in CH2Cl2 and the solvent was rapidly removed to leave the product as a colorless solid (0.067 g, 54%). Anal. Calc. for C64H59F6P5Pd2: C, 58.68; H, 4.51. Found: C, 58.39; H, 4.62%. 1H NMR (CDCl3): d − 9.16 (q, 1H, 2J(PH) = 15 Hz, m-H); 1.87 (s, 6H, CH3); 4.09 (m, 4H, PCH2P); 6.17 (d, 4H, 3J(HH)= 8 Hz, C6H4Me); 6.33 (d, 4H, 3J(HH) = 8 Hz, C6H4Me); 7.1 – 7.4 (m, 40H, PPh2). 31P{1H} NMR: d 15.6 (s). Following a separate experiment, in which NaBH3CN was used instead of NaBH4, slow evaporation of a CH2Cl2 –pentane solution of the product at − 40°C gave [Pd2(C6H4Me-4)2(m-H)(m-dppm)2]BH3CN as orange plates.
3.2. Preparation of [Pd2Ph2(m-H)(m-dppm)2]PF6 (1b) The phenyl derivative was prepared similarly, and isolated as a gray solid in 80% yield. 1H NMR (CDCl3): d − 9.05 (q, 1H, 2J(PH) =15 Hz, m-H); 4.09 (m, 4H, PCH2P); 6.3–6.6 (m, 10H, PdPh); 7.2 – 7.9 (m, 40H, PPh2). 31P{1H} NMR: d 16.9 (s).
3.3. Preparation of [Pd2Me2(m-H)(m-dppm)2]PF6 (1c) This complex was prepared analogously and obtained as a gray solid in 74% yield. 1H NMR (CDCl3): d −7.55 (q, 1H, 2J(PH) = 16 Hz, m-H); 0.07 (s, 6H, CH3); 4.55 (m, 4H, PCH2P); 7.2 – 7.9 (m, 40H, PPh2). 31 P{1H} NMR: d 23.4 (s).
3.4. Preparation of [Pd2Et2(m-H)(m-dppm)2]PF6 (1d) The ethyl complex was prepared similarly and isolated as a gray solid in 54% yield. Anal. Calc. for C54H55F6P5Pd2: C, 54.69; H, 4.64. Found: C, 54.16; H, 4.65%. 1H NMR (CDCl3): d −7.79 (q, 1H, 2J(PH)= 16 Hz, m-H; − 0.07 (t, 6H, 3J(HH) = 7 Hz, CH2CH3); 1.05 (quartet, 4H, 3J(HH) = 7 Hz, CH2CH3); 4.50 (m, 4H, PCH2P); 7.2–7.9 (m, 40H, PPh2). 31P{1H} NMR: dP 23.9 (s).
3.5. Preparation of [Pd2(n-Bu)2(m-H)(m-dppm)2]PF6 (1e) This complex was prepared by the above method and was obtained as a gray solid in 45% yield. Anal. Calc. for C54H55F6P5Pd2: C, 56.10; H, 5.08. Found: C, 56.61; H, 5.07%. 1H NMR (CDCl3): d −7.68 (q, 1H, 2 J(PH)=16 Hz, m-H); −0.26 (t, 6H, 3J(HH) = 7 Hz, CH3); 0.09 (m, 8H, CH2CH2CH3); 0.95 (m, 4H, PdCH2); 4.05 (m, 4H, PCH2P); 7.2 – 7.9 (m, 40H, PPh2). 31 P{1H} NMR: d 22.5 (s).
3.6. Preparation of [Pd2(COMe)2(m-H)(m-dppm)2]PF6 (1f) Tetramethyltin (0.042 ml, 0.31 mmol) was introduced to a CH2Cl2 suspension (30 ml) of [Pd2Cl2(m-Cl)2(AsPh3)2] (0.10 g, 0.10 mmol). The mixture was allowed to stir for 3 h, CO was bubbled through it for a further 1 h, then dppm (0.079 g, 0.21 mmol), methanol (1 ml) and TlPF6 (0.072 g, 0.21 mmol) were added. The solvents were removed, the residue was washed with ether and pentane, then redissolved in CH2Cl2 and passed through a short column of neutral alumina, eluting with CH2Cl2 (30 ml). The resulting solution was cooled to −78°C and NaBH4 (0.21 ml of a 0.5 M solution in 2-methoxyethyl ether) was added by syringe, followed by TlPF6 (0.072 g, 0.21 mmol). The solvents were removed under reduced pressure while the flask was gradually warmed to ambient temperature, and the resulting dark solid was washed with hexane and ether. Extraction with CH2Cl2 (30 ml) gave a dark solution, which was passed through a neutral alumina column, eluting with CH2Cl2. The resulting pale-yellow solution was evaporated to dryness, and the crude product was crystallized twice from CH2Cl2 –ether. The crystals were redissolved in CH2Cl2 and the solvent was rapidly removed to leave a brown solid (0.079 g, 63%). Anal. Calc. for C54H51F6O2P5Pd2: C, 53.43; H, 4.21. Found: C, 53.35; H, 4.37%. 1H NMR (CDCl3): dH − 10.24 (q, 1H, 2J(PH)= 18 Hz, m-H); 1.10 (s, 6H, COCH3); 4.02 (m, 4H, PCH2P); 7.2–7.5 (m, 40H, PPh2). 31P{1H} NMR: dP 12.2 (s).
3.7. Preparation of [Pd2(COEt)2(m-H)(m-dppm)2]PF6 (1g) This complex was prepared by the above method and was obtained as a brown solid in 45% yield. Anal. Calc. for C56H55F6O2P5Pd2: C, 54.16; H, 4.43. Found: C, 53.76; H, 4.39%. 1H NMR (CDCl3): dH –9.99 (q, 1H, 2 J(PH)= 18 Hz, m-H); 0.01 (t, 6H, 3J(HH)=7 Hz, CH2CH3); 1.64 (quartet, 4H, COCH2CH3); 3.94 (m, 4H, PCH2P); 7.2–7.6 (m, 40H, PPh2). 31P{1H} NMR: dP 12.5 (s).
3.8. Preparation of [Pd2(COBn)2(m-H)(m-dppm)2]PF6 (1h) This complex was prepared by the above method and was obtained as a brown solid in 61% yield. 1H NMR (CDCl3): dH –10.10 (q, 1H, 2J(PH)= 18 Hz, m-H); 3.02 (s, 4H, COCH2Ph); 4.02 (m, 4H, PCH2P); 5.79 (d, 4H, 3J(HH)= 8 Hz, C6H5-2,6); 6.85 (t, 4H, 3J(HH)=8 Hz, C6H5 -3,5); 6.91 (t, 2H, 3J(HH)= 8 Hz, C6H5 -4); 7.2-7.6 (m, 40H, PPh2). 31P{1H} NMR: dP 12.3 (s).
R.A. Stockland Jr. et al. / Inorganica Chimica Acta 300–302 (2000) 395–405
3.9. Preparation of [PdPt(C6H4Me-4)2 (m-H)(m-dppm)2]PF6 (2a) A stirred CH2Cl2 solution (30 ml) of [PdPtCl2(mdppm)2] (0.10 g, 0.088 mmol) was cooled to − 78°C and 4-tolylmagnesium bromide (1.0 ml of a 1.0 M ether solution) was introduced. The solution darkened and was stirred for 14 h. Methanol (1 ml), CBr4 (0.10 g, 0.30 mmol), and TlPF6 (0.031 g, 0.089 mmol) were added and the flask was allowed to warm to ambient temperature while the solvents were removed under reduced pressure. After washing with ether and hexane, the solid residue was extracted with CH2Cl2 and passed through a short column of neutral alumina, eluting with CH2Cl2 (50 ml). The resulting solution was again cooled to − 78°C and NaBH4 (0.18 ml of a 0.5 M solution in 2-methoxyethyl ether) was added by syringe, followed by TlPF6 (0.031 g, 0.089 mmol). The solvent was removed under reduced pressure while the flask was gradually warmed to ambient temperature, and the resulting dark solid was washed with pentane and ether. Extraction with CH2Cl2 gave a dark solution, which was passed through a neutral alumina column, eluting with CH2Cl2. The resulting pale-yellow solution was evaporated to dryness, and the crude product was crystallized twice from CH2Cl2 – ether. The crystals were re-dissolved in CH2Cl2 and the solvent was rapidly removed to leave a brown solid (0.075 g, 57%). Anal. Calc. for C64H59F6P5PdPt: C, 54.96; H, 4.23. Found: C, 54.96; H, 4.24%. 1H NMR (CDCl3): d − 8.97 (q, 1H, 2 J(PH)=11 Hz, 1J(PtH) =540 Hz, m-H); 1.85 (s, 6H, CH3); 4.34 (m, 4H, 3J(PtH) =38 Hz, PCH2P); 6.1–6.4 (m, 8H, C6H4Me); 7.2 – 7.8 (m, 40H, PPh2). 31P{1H} NMR: d 13.5 (m, 1J(PtP) =2955 Hz). Slow evaporation of a CHCl3 –Et2O solution gave the complex as colorless needles.
403
0.35 mmol) was added dropwise, followed by TlPF6 (0.12 g, 0.35 mmol). The solvent was removed under reduced pressure and, after washing with ether and pentane, the residue was extracted with CH2Cl2 and filtered. The yellow solution was passed through a 5-cm neutral alumina column, eluting with CH2Cl2, then cooled to − 78°C. NaBH4 (0.70 ml of a 0.5 M solution in 2-methoxyethyl ether) was added, followed by TlPF6 (0.12 g, 0.35 mmol), then the solvent was removed under reduced pressure while the flask was allowed to warm to ambient temperature. After washing with ether and pentane, extraction with CH2Cl2 produced an orange solution, which was passed through a neutral alumina column, eluting with CH2Cl2 (50 ml). The solvent was removed and the product was crystallized twice from CH2Cl2 –ether. The crystals were re-dissolved in CH2Cl2 and the solvent was rapidly removed to give an orange solid (0.18 g, 42%). Anal. Calc. for C60H59F6P5Pd2: C, 57.10; H, 4.68. Found: C, 56.89; H, 4.70%. 1H NMR (CDCl3): d −7.87 (q, 1H, 2J(PH)= 15 Hz, m-H); 0.01 (t, 3J(PH)= 6 Hz, PdCH3); 1.84 (s, 3H, 4-CH3); 1.91 (s, 6H, 2,6-CH3); 4.01 (br s, 4H, PCH2P); 5.94 (s, 4H, C6H2Me3); 7.0–7.8 (m, 40H, PPh2). 31P{1H} NMR: d 20.9 (m, 2P, P2PdMe); 16.1 (m, 2P, P2PdMes).
3.12. Preparation of [Pd2(C6H2Me3 -2,4,6)Et(m-H)(m-dppm)2]PF6 (3b)
The phenyl analogue was prepared analogously, and the product was obtained as a pale-yellow solid (0.076 g, 64%). 1H NMR (acetone-d6): d − 9.04 (q, 1H, 2 J(PH)=11 Hz, 1J(PtH) = 535 Hz, m-H); 4.40 (m, 4H, 3 J(PtH)=43 Hz, PCH2P); 7.2 – 7.8 (m, 50H, C6H5). 31 P{1H} NMR: d 15.2 (m, 1J(PtP) =2853 Hz).
The complex was prepared as above starting from [PdCl2(cod)] (0.10 g, 0.35 mmol) and 2-mesitylmagnesium bromide (0.53 ml of a 1.0 M ether solution). A CH2Cl2 solution of [Pd2Et2(m-Cl)2(AsPh3)2] (prepared from [Pd2(m-Cl)2Cl2(AsPh3)2] (0.17 g, 0.18 mmol) and Et4Sn (0.10 ml, 0.52 mmol) in CH2Cl2 (20 ml)) was added dropwise in the second step. After reaction with NaBH4 and TlPF6, the product was obtained as an orange solid (0.20 g, 45%). 1H NMR (CDCl3): d −7.95 (q, 1H, 2J(PH)= 16 Hz, m-H); − 0.01 (m, 2H, PdCH2); 1.10 (m, 3H, CH3); 1.86 (s, 3H, 4-CH3); 2.01 (s, 6H, 2,6-CH3); 3.99 (br s, 4H, PCH2P); 5.95 (s, 2H, C6H2Me3); 7.0–7.8 (m, 40H, PPh2). 31P{1H} NMR: d 20.5 (m, 2P, P2 PdEt); 16.0 (m, 2P, P2 PdMes). Slow evaporation of a CH2Cl2 –Et2O solution resulted in crystallization of the complex as orange cuboids.
3.11. Preparation of [Pd2(C6H2Me3 -2,4,6)Me(m-H)(m-dppm)2]PF6 (3a)
3.13. Preparation of [Pd2(C6H2Me3 -2,4,6)Ph(m-H)(m-dppm)2]PF6 (3c)
A stirred CH2Cl2 solution (30 ml) of [PdCl2(cod)] (0.10 g, 0.35 mmol) was cooled to −78°C and 2mesitylmagnesium bromide (0.53 ml of a 1.0 M solution in ether) was added by syringe. After 30 min, methanol (1.0 ml) was added along with dppm (0.27 g, 0.70 mmol). The solution was stirred for 14 h, then a CH2Cl2 solution (20 ml) of [PdClMe(cod)] (0.093 g,
The complex was prepared from [PdCl2(cod)] (0.10 g, 0.35 mmol) and 2-mesitylmagnesium bromide (0.53 ml of a 1.0 M solution in ether). A CH2Cl2 solution (20 ml) of [Pd2Ph2(m-Cl)2(AsPh3)2] (0.18 g, 0.18 mmol) was added dropwise in the second step. After reaction with NaBH4 and TlPF6, the product was isolated as an orange solid (0.28 g, 59%). Anal. Calc. for
3.10. Preparation of [PdPtPh2(m-H)(m-dppm)2]PF6 (2b)
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C65H62F6P5Pd2: C, 58.92; H, 4.68. Found: C, 58.69; H, 4.77%. 1H NMR (CDCl3): d −8.66 (q, 1H, 2J(PH)= 15 Hz, m-H); 1.87 (s, 3H, 4-CH3); 2.01 (s, 6H, 2,6-CH3); 4.05 (s, 4H, PCH2P); 5.94 (s, 2H, C6H2Me3); 6.3–6.6 (m, 5H, PdPh); 7.0 – 7.8 (m, 40H, PPh2). 31P{1H} NMR: d 15.9 (m, 2P, P2PdPh); 14.2 (m, 2P, P2PdMes). Slow evaporation of a CH2Cl2 – C6H6 – Et2O solution gave the complex as pale-yellow crystals.
3.14. X-ray structure determinations For complexes 1a, 2a, 3b and 3c, preliminary examination and data collection were performed using a Siemens SMART CCD detector system single-crystal X-ray diffractometer equipped with a sealed tube X-ray source (50 kV × 40 mA) using graphite-monochromated Mo Ka radiation (l =0.71073 A, ). Preliminary unit cell constants were determined with a set of 45 narrow frame (0.3° in 6) scans. The double pass method of scanning was used to exclude any noise. The collected frames were integrated using an orientation matrix determined from the narrow frame scans. The SMART software package [24] was used for data collection and SAINT [24] was used for frame integration. Final cell constants were determined by a global refinement of xyz centroids of 8192 reflections. An empirical absorption correction was applied using SADABS [25]. Structure solution and refinement were carried out using the SHELXTL-PLUS (5.03) software package [26].
For complex 4 preliminary examination and data collection were performed using a Siemens R3 singlecrystal X-ray diffractometer using graphite-monochromated Mo Ka radiation (l= 0.71073 A, ). Autoindexing of 10 centered reflections from the rotation photograph resulted in a triclinic cell. Axial photographs were taken to confirm the cell lengths. Final cell constants and orientation matrix for data collection were calculated by least-squares refinement of the setting angles for 30 reflections (32°B 2u B 35°). Intensity data were collected using v/2u scans with variable scan speed. Three representative reflections measured every 50 reflections showed B 12% variation during data collection. Data reduction was carried out by XDISK [24]. In each case, the structure was solved by Patterson methods and refined successfully in the space group given in Table 7. Full-matrix least-squares refinement was carried out by minimizing Sw(F o2 − F c2)2. The non-hydrogen atoms were refined anisotropically to convergence. The hydrogen atoms were treated using appropriate riding models (AFIX m3). Crystal data and structure refinement parameters are given in Table 7. The mesityl compounds are not disordered, but the three other compounds exhibit positional disorder. Compounds 1a and 4 crystallize in the triclinic space group P1( . In 1a the cation is not disordered, as would be expected since the metal and ligands are identical in both halves of the A-frame. The cation and the BH3CN− anion are located around an inversion center, so 50% of the A-frame is unique and there are two
Table 7 Crystallographic data for complexes 1a, 2a, 3b, 3c and 4 Complex
1a
2a
3b
3c
4
Crystal system Space group Unit cell dimensions a (A, ) b (A, ) c (A, ) a (°) b (°) g (°) V (A, 3) Z Dcalc (Mg m−3) Temperature (K) Absorbtion coefficient (mm−1) u Range (°) Reflections collected Independent reflections Observed reflections Absorption correction No. parameters refined R(F), Rw(F 2) (F 2\2.0s(F 2)) R(F), Rw(F 2) (all data) Goodness of fit Largest difference peak, hole (e A, −3)
triclinic P1(
monoclinic P21/n
monoclinic C2/c
monoclinic P21/n
triclinic P1(
11.5028(1) 12.4083(1) 12.4609(2) 106.587(1) 93.100(1) 116.809(1) 1486.16(3) 1 1.346 223(2) 0.752 1.75 to 28.00 44 293 7139 7139 empirical 355 0.0440, 0.1207 0.0689, 0.1350 1.025 1.051, −1.055
14.6934(2) 26.0200(1) 16.9169(1) 90 96.59(1) 90 6424.97(10) 4 1.568 223(2) 2.760 1.44 to 25.00 73 690 11 294 11 225 empirical 754 0.0635, 0.1391 0.1368, 0.1742 1.068 1.454, −1.389
43.7235(6) 12.1038(2) 23.7965(1) 90 115.095(1) 90 11 404.8(2) 8 1.486 223(2) 0.829 1.73 to 25.00 60 162 10 058 10 058 empirical 671 0.0601, 0.1130 0.1688, 0.1488 0.947 0.828, −0.766
12.2426(2) 22.8016(3) 26.5958(4) 90 101.707(1) 90 7269.8(2) 4 1.388 218(2) 0.663 1.19 to 25.00 132 945 12 807 12 807 none 818 0.0552, 0.1239 0.1166, 0.1551 1.001 0.676, −0.624
10.853(2) 12.080(2) 12.179(2) 84.570(10) 72.840(10) 87.990(10) 1518.8(5) 1 1.639 298(2) 3.046 1.69 to 27.56 7388 7017 7017 empirical 340 0.0644, 0.1285 0.1169, 0.1542 1.047 1.075, −0.963
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unique disordered BH3CN− fragments. The site C1% of the first BH3CN− fragment is coincident with B1% for the second fragment. All atoms of the anion were refined with 25% occupancy factors. In 4 the cation is disordered. The molecule is centered around the inversion center making 50% of the molecule unique. Therefore, the Pt and Pd sites and the ligands attached to the metals (Et and Me) are disordered. The disorder was modeled as 50% occupancy for the metals and the Et/Me fragments. The mixed metal compound 2a crystallizes in the monoclinic space group P21/n. The metal positions are disordered and were refined with 50% occupancy at both sites.
4. Supplementary material Atomic coordinates and anisotropic displacement coefficients for the non-hydrogen atoms, positional and isotropic displacement coefficients for the hydrogen atoms, complete lists of bond distances and angles, and calculated and observed structure factors are available form the author. Crystallographic data for the structural analysis has been deposited with the Cambridge Crystallographic Data Centre, CCDC 134200 for compound 1a, 139844 for compound 4, 139845 for compound 2a, 139846 for compound 3b and 139847 for compound 3c. Copies of this information may be obtained free of charge from: The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: + 441223-336-033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk).
Acknowledgements Thanks are expressed to the National Science Foundation (grant no. CHE-9508228) for support of this work, to Mallinckrodt Inc. for a fellowship (to RASJ), and to the National Science Foundation (grant nos. CHE-9318696 and 9309690), the US Department of Energy (grant no. DE-FG02-92CH10499) and the University of Missouri Research Board for instrumentation grants.
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