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New paramagnetic pyrazole complexes of tris(3,5-dimethylpyrazolyl)borato molybdenum nitrosyl chloride and iodide and the structure of [Mo(NO)HB(3,5-Me2C3HN2)3Cl(3,5-Me2C3HN2H)]
Polyhedron Vol. 12. No. I, PP. 715-719, Printed in Great Britain
0277-5387/93 $6.OQ+ 40 Pergamon Press Ltd
1993
NEW’ PARAMAGNETIC PYRAZOLE COMPLEXES OF TRIS(3,5-DIMETHYLPYRAZOLYL)BORATO MOLYBDENUM NITROSYL CHLORIDE AND IODIDE AND THE STRUCTURE OF [Mo(NO){HB(3,5-Me2C$IN2)3)C1(3,5-Me&HN,H)] ANDRZEJ
WLODARCZYK
and STEFAN S. KUREK
Institute of Chemical Engineering and Physical Chemistry, Technical University of Krakow, 3 1- 155 Krakow, Poland and JOHN P. MAHER, ANDRE1 S. BATSANOV,? JUDITH and JON A. McCLEVERTYS
A. K. HOWARD?
School of Chemistry, University of Bristol, Cantocks Close, Bristol BS8 lTS, U.K. (Received 13 October 1992; accepted 2 December 1992)
Abstract-Reduction of [Mo(NO)L*Cl,] [L* = HB(3,5-Me,C,HN,),] with n-butyl lithium in the presence of SnBua3Cl afforded the paramagnetic (17-electron) [Mo(NO)L*C1(3,5Me,C3HN2H)] (1). Related compounds, [Mo(NO)L*XQ] (Q = pyrazole, 3,5-dimethylpyrazole, 4-bromopyrazole and 4-bromo-3,5_dimethylpyrazole ; X = Cl or I), were prepared by the reduction of [Mo(NO)L*X,] by Q (X = I) or by n-butyl lithium in the presence of Q (X = Cl). IR and EPR spectroscopic characterization of these species is reported and the Xray structure of [Mo(NO)L*C1(3,5-Me2C3HN2H)] - 1/2CHzC12, in which the molybdenum atom has octahedral coordination with disordered Cl and NO ligands, is described.
In an attempt to functionalize the pyrazolyl rings of the tris(3,5-dimethylpyrazolyl)borato ligand HB(3,5-Me2C3HN,)3 (L*) at the 4-positions we have investigated the reactions of [Mo(NO)L*Cl,] with LiBu” and SnBu”,Cl, our intention being to introduce the SnBu”, group onto at least one pyrazole ring in the coordinated tripodal ligand. In previous studies of the reactions of [Mo(NO)L*I,] with organo-lithium reagents we had observed that the reduction of the metal complex rather than displacement of I- by a carbanion was the dominant reaction. ’ This we could rationalize in terms of the reducing nature of the lithium organyl and the particularly accessible reduction potential of the molybdenum di-iodide (+0.33 V vs S.C.E. in CH3CN)
and also in terms of the apparent steric difficulty in generating a potential four-centred intermediate or transition state necessary to effect interchange of I by an organic group at the metal in the hindered {Mo(NO)L*I) entity. Indeed, treatment of No (NO)L*I,] with tolyl lithium in ether afforded [Mo(NO)L*12Li(OEt2)~], which contains the paramagnetic [Mo(NO)L*I,]- centre stabilized by the {Li(OEtz)Z}+ fragment. However, the reduction potential of [Mo(NO)L*Cl,] is significantly more anodic (-0.01 V vs S.C.E. in CH$N) than that of its iodo-analogue, and we reasoned that, because of this and the well-understood steric protection afforded by L* at the MO centre,’ reactivity might be diverted preferentially to the pyrazolyl rings of L*. In this paper we describe the reactions of [MO TPresent address : Department of Chemistry, Uni- (NO)L*X,] (X = Cl or I) with n-butyl lithium and versity of Durham, South Road, Durham DHl 3LE, SnBu”,Cl, in which partial decomposition of the U.K. nitrosyl complex with disruption of the tris(pyrazo$ Author to whom correspondence should be addressed. 1yl)borato ligand and reduction of the basic halide 715
716
A. WLODARCZYK
system occurred, and we report on the consequent formation of the paramqgnetic 3,5-dimethylpyrazole complex Flo(NO)L*X(3,5-Me,C,HN,H)] (1). Using reductive proceduq’es we have also prepared related complexes contairjing pyrazole (C3H3N2H), 4-bromo-(4-BrC3H2N2H) and 4-bromo-3,5dimethylpyrazole (3,5- eZ-4-BrC3N2H). These paramagnetic pyrazole l\r~complexes are closely related to the pyridine an 4,4’-bipyridyl complexes [Mo(NO)L*Cl(py)] and1 [Mo(NO)L*Cl(NCSH4 -C,H,N)], which have1 been briefly described elsewhere. 3 EXPERIMENTAL Synthetic studies
All reactions werecarrie out in an atmosphere of dry nitrogen. Toluene was redistilled from sodium benzophenone before use. o(NO)L*Cl,] was prepared as described elsew & re,4 butyl lithium was used as a 1.6 M solutio$ in hexane and other reagents were used as r ived. Column chromatography was carried !ce ut using 70-230 mesh silica gel. IR spectra were] recorded in KBr discs using a PE 1600 FTIR pectrometer and EPR spectra were recorded in \ ichloromethane using a Bruker ESP 300E instrunient.
General procedure for the ‘synthesis of [Mo(NO) L*IQ] (Q = C3H3N2H, 4- rC3HN2H, 3,5-Me& i H2H and 3,5-Me,-4-BrC,NhH)
A solution of [Mo(NO)LV,] (0.3 g) and pyrazole (0.09 g) or substituted pyra ole (1: 2 mole ratio) in toluene (30 cm’) was stirre at 80-90°C for 15-60 min, depending on the kind of pyrazole. The solution became deep green nd the solvent was removed in vacua, the resi ue being redissolved in dichloromethane. The s1 lution was chromatographed on silica gel, usin dichloromethane as een fraction was colan eluant, and the main lected. The solvent was evap rated and the residue recrystallized from dichl romethane/petroleum ether (b.p. 40--6O”C), affordi :; g green crystals. The yields were variable (30-50%). General procedure for the s nthesis of [Mo(NO) L*ClQ] (Q = C3H3N2H and t” 3,5-Me2C3HN2H] A solution of [Mo(NO)L Cl*] (0.3 g) and the appropriate pyrazole (2 mo 1es per mole of molybdenum complex) was wa ed to facilitate discomplex and then solution of the cooled to ca 60°C. Butyl lithi in hexane (0.8 cm3)
et al.
was added and the reaction mixture stirred for 1 h, during which time the solution became grey-green in colour. Petroleum ether (b.p. 40-6O”C) was added to precipitate salts and the solution was filtered, evaporated to dryness in vucuo and redissolved in the minimum volume of dichloromethane. The product was then obtained in the same way as the corresponding iodo complex and was isolated as green crystals (yields variable, 25-35%). Crystal strucfure determination of [Mo(NO)L*Cl
W-Me2C3HNzHll(1) A suitable crystal of the compound (a green plate sized 0.25 x 0.35 x 0.40 mm) was grown from dichloromethane/petroleum ether (b.p. 60-SO’C). Crystal data. Cz,,H30N90BC1Mo * 1/2CHzC12, M = 597.2, monoclinic, space group C2/c, a = 20.625(5), b = 10.858(2), c = 24.413(6) A, p’ = 96.23(2)“, U = 5.435(2) w3, Z = 8, D, = 1.46 g cm- 3, F(OO0) = 2.448, graphite-monochromated MO-K, radiation, R = 0.71069 A, p = 7.1 cm-‘. A total of 4000 independent reflections with 20 -=z47” were collected in the Wyckoff (limited w) scan mode. The reflection intensities were corrected for absorption, using the semi-empirical method,’ based on 396 azimuthal scans of 11 reflections (min. and max. transmission coefficients 0.5524 and 0.5744, respectively). The structure was solved by Patterson and Fourier methods and refined by fullmatrix least-squares using SHELXTLPLUS6 programs. Difference-Fourier maps revealed a disorder in the coordination sphere of the molybdenum atom, the Cl and NO ligands mixing at each site. Their occupancy factors were refined, yielding 0.65(2) for positions A and 0.35(2) for B (of both ligands). In the final refinement these atoms were treated in isotropic approximation, while all other non-hydrogen atoms were refined with anisotropic displacement parameters. Most of the hydrogen atoms were revealed by difference-Fourier syntheses, but all of them were included in the refinement in riding model in idealized positions, with the distances C-H 0.96, N-H 0.90 and B-H (from Fourier map) 1.07 A. The refinement of 310 variables converged at R = 0.041 and R’ = 0.052 for 3298 reflections with I > 2a(0 The weighting scheme w- ’ = 02(F) + 0.002F2 was used ; goodness of fit was 2.22. The maximum and minimum residuals in the final AF map were 0.56 and - 0.42 e A- 3 (around the disordered atoms). Selected bond lengths and angles are given in Table 1. Additional data (atom coordinates, thermal parameters and remaining bond lengths and angles) are available from the Cambridge Crystallo&aphic Data Centre.
717
Structure of [Mo(NO)(HB(3,5-Me,C,HN&jCl(3,5-Me,C,HNzH)] Table 1. Selected bond lengths (A) and angles (“) Mo-Cl(lA) Mo-N(OA) MO-N( 1) MO-N(21) N(OA)--O(lA) N(l)--N(2) N(2)-C(3) C(3)--c(6) C(5)_C(7) N(ll)--C(U) N(12)--B C(13)-C(16) CU5Fw7) N(21)--C(25) N(22)-B C(23)--c(26) C(25)-C(27) N(3 lFC(35) N(32)-B C(33)--c(36) C(35)--c(37)
2.420(4) 1.782(12) 2.199(4) 2.217(4) 1.127(18) 1.359(6) 1.343(6) 1.498(8) 1.494(8) 1.333(6) 1.529(7) 1.495(8) 1.477(8) 1.342(6) 1.541(7) 1.497(8) 1.486(7) 1.342(6) 1.531(7) 1.493(8) 1.474(8)
Cl(lB)--MO-N(OB) Cl( lB)-Mo-N( 1) N(OB)-MO--N(~) Cl(lB)--MC+-N(ll) N(OB)-MO-N(l 1) Cl(lA)-MC+N(21) N(OA)--Mo-N(21) N(l)--MO-N(21) Cl(lA)-Mo-N(31) N(OA)--MO-N(3 1) N(l)-MO-N(31) N(21)--MO-N(31)
91.4(5) 91.9(2) 91.6(6) 95.3(2) 91.4(6) 91.1(l) 175.5(3) 87.6(l) 174.8(l) 91.5(3) 92.7( 1) 84.1(l)
RESULTS AND DISCUSSION
Synthetic and spectral studies On addition of n-butyl lithium to lJvlo(NO)L*Cl,] partially
dissolved
in toluene,
in a mole ratio of
2 : 1, a red colour developed, but further addition of
LiBu” was necessary to complete dissolution of the molybdenum chloride and generate a homogeneous deep red solution. On addition of SnBu”,Cl the solution darkened and on work-up, which involved chromatography over silica, paramagnetic 1 was formed as green crystals. This species was characterized by elemental analysis (Table 2) and by IR and EPR spectroscopy. The yield of the species was of the order 20% and it is clear that the generation of this 17-electron 3,5-dimethylpyrazole species must occur via decomposition of the starting
Mo-CI(lB) MO-N(OB) Mo-N( 11) MO-N(3 1) N(OBF-WB) N(1 k-C(5) C(3)_C(4) C(4)--c(5) N(ll)--N(12) N02k-w3) C(l3I--w4) C(14Fw5) N(21)--N(22) N(22wx23) C(23FJ24) C(24>--c(25) N(31)-N(32) N(32)-C(33) C(33)-C(34) C(34wx35) c1(10)--C(10)
2.423(9) 1.797(22) 2.162(4) 2.204(4) 1.199(34) 1.335(6) 1.349(7) 1.390(7) I .374(6) 1.357(6) 1.361(9) 1.376(8) 1.375(5) 1.346(6) 1.382(8) 1.381(7) 1.385(5) 1.356(6) 1.360(7) 1.391(7) 1.680(g)
Cl( 1A)--MO-N(OA) Cl( 1A)--MO-N( 1) N(OA)-Mo-N(1) Cl( 1A)-MO-N( 11) N(OA)-M+-N( 11) N(l)--MO-N(ll) CI(IB)-MO-N(21) N(OB)--MO-N(21) N( 1I)-Mo-N(21) Cl(lB)--MO-N(31) N(OB)--MO-N(31) N(ll)-MO-N(31) MO-N(OA)--O( 1A)
93.3(3) 89.2( 1) 91.5(3) 93.6(l) 95.7(3) 172.1(l) 175.0(2) 93.5(5) 84.9( 1) 90.9(2) 175.0(6) 84.0( 1) 178.2(8)
material, possibly via the reduced, 17-electron species [Mo(NO)L*Cl,]-. Furthermore, we had also previously observed that in reaction of [MO (NO)L*I,] with oxacyclohexane7 reduction of the molybdenum species and formation of the 3,5_dimethylpyrazole adduct, [Mo(NO)L*I(3,5Me2C3HN2H)], occurred. In a similar reaction with [Mo(NO)L*I,] 1 was again formed, probably because of the inclusion of SnBu*&l in the reaction mixture. We have observed on numerous occasions that iodine may be replaced by chlorine in reaction systems derived from [Mo(NO)L*I,] in the presence of chlorinated hydrocarbons.’ The yield of the pyrazole complexes was ca 20%. In a modification of the route to these 17-electron heterocycle complexes [Mo(NO)L*Cl,] was reduced by LiBu” in the presence of a suitable
718
A. WLODARCZYK et al. Table 2. Elemental analytical data and NO stretching frequencies for [Mo(NO)L*XQ]
Compound [Mo(NO)L*CI(Mq,C,HN,H)] [Mo(NO)L*Cl(C,@,N,H)I [Mo(NO)L*I(Me&HN,H)] [Mo(NO)L*I(C,H f N,H)] [Mo(NO)L*I(BrC H2N2H)] [Mo(NO)L*I(Me, rC,N,H)]
C
Found H
N
IR WO) (cm- ‘)
42.9 41.2 36.2 36.3 31.3 33.5
5.9 5.1 4.9 4.7 3.8 4.2
21.7 23.8 19.5 20.3 18.7 17.8
1610 1610 1617 1616 1618 1617
Calculated C H N 43.3 41.0 37.2 35.0 31.0 33.1
5.4 5.0 4.7 4.2 3.6 4.0
pyrazole Q (C3H3N2H, 3,5-MezC3HN2H, 4-BrC3H2 N,H), the desired comple b([Mo(NO)L*CIQ] being isolated in yields varying from 25 to 35%. However, [Mo(NO)L*12] react d directly with the pyrazoles Q (C3H3N2H, 3,5- t e2C3HN2H, 4-BrC3H2 N2H and 4-Br-3,5-Me,C,HzH), without the necessity of the lithium organylb affording modest yields of the 17-electron [Mo(Nb)L*IQ]. This last reaction may be compared 4th our earlier observations’ that the di-iodide reacted with an excess of pyrazole Q (C3H3NZH, 3,$-Me2C3HN2H), affording the cutionic 17-electron species lMo(NO)L*Qd+. The IR spectra of the ne compounds are entirely consistent with our form lations. In addition to exhibiting the normal stre hing modes associated with L* [e.g. v(BH) at ca 2,50 cm-‘] they show an i NO stretching frequency ip the range 1610-1618 - I, which is broadly co parable to the position rzthe related pyridine speci, 1 s [Mo(NO)L*C~(~~)J,~ but significantly lower than the corresponding bis(pyrazole) species [Mo(NO)L*Q,]+,~ as would be expected on the grounds of the nature of the ligands and positive charge. The complexes [Mo( O)L*XQ] (X = Cl, Q= C3H3N2H and 3,5- e$,HN,H; X = I, Q = C3H3N2H) exhibit EP spectra (Table 3) conc taining a signal at giw close to 1.976, with additional hyperfine coupling, A,,, of da 46 x 1O-4 cm- *, due to the I= 512 isotopes [95Mo (15.9%) and 97Mo (9.6%)]. These spectral par meters are similar to those obtained from [Mo(N )L*Cl(py)] (giso 1.970, d A,,, 45.7 x lop4 cm- ‘)’ and [Mo(NO)L*(pyrazole)$ (giiso 1.973-1.977, iAM043.8-46.0 X 10B4 cm- I). 9 The data are broad1 consistent with localization of the unpaired electr n on the metal centre. However, the EPR spectr4 m of [Mo(NO)L*I (3,5-Me,C3HN2H)] shows gi = 2.0036 and A,,. = 43.2 x 1O-4 cm- ‘, which di rs significantly from the other three species. We h ve no simple explanation for this observation, f, t it may arise from some form of distortion in the molecule.
22.7 23.9 19.5 20.4 18.1 17.4
Crystal structure of [Mo(NO)L*C1(3,5-Me2C3HN2
WI (1) The asymmetric unit of the structure contains one molecule of 1 in a general position and half of a CH$l, molecule, whose carbon atom is situated on a two-fold axis, thus corresponding to the stoichiometry [Mo(NO)L*C1(3,5-Me$,HN,H)] 1/2CHzC12. The molybdenum atom has distorted octahedral coordination, with one chlorine and five nitrogen atoms. The disorder (mixing) of Cl and NO ligands can be explained in terms of both R and S enantiomers of 1 occupying statistically the same crystallographic position (the crystal itself being centrosymmetric and racemic). The Mo-N bond lengths associated with the tris(pyrazolyl)borate and the 3,5_dimethylpyrazole ligands are similar (average 2.20 A) and reveal little difference in tram influence due to the Cl and NO groups (this also being a result of the nature of the disorder). As expected the Mo-N-O bond angle is essentially linear and the MO-N(O) distance (mean 1.79 A) is close to the usual (1.76-1.80 A).” In nitrosyl complexes of molybdenum with filled dxz and d,, orbitals, other ligands having filled pnorbitals or lone electron pairs tend to adopt the orientation with these orbitals approximately
Table 3. EPR spectral data obtained from [Mo(NO)L*
XQI A,,. x IO4 X
Q
Cl Cl I I
CxH,NzH 3,5-Me,C,HN2H CxHsNzH 3,5-Me2C,HNzH ..
.
Sk0
(cm- ‘)
1.9768 1.9768 1.9760 2.0036
46.2 46.1 45.34 43.22
Structure of [Mo(NO){HB(3,5-Me,C,HN&}C1(3,5-Me,C,HN,H)]
719
The only active hydrogen atom, at N(2), does not participate in hydrogen bonding. Acknowledgements-We are grateful to the British Council, through a Tripartite Acciones Integradas Programme, for partial support of this work (S.K. and A.W.), to the Politechnika Krakowska, Poland, for leave of absence (S.K. and A. W.), to the Royal Society for a Visiting Fellowship (A.S.B.) and to the SERC for financial assistance (EPR spectrometer). REFERENCES
J.
Fig. 1. Molecular structure of [Mo(NO)L*C1(3,5Me2C3HN2H] (1). For clarity, only the major (A) positions of Cl and NO ligands are shown (in B positions these ligands are interconverted), and all methyl hydrogens are omitted.
4.
5.
orthogonal to the NO group, thereby maximizing is the d,,-p overlap. ” In 1 such an orientation impossible due to the steric hindrance imposed by the methyl substituents of the pyrazolyl rings ; torsion angles N(OA)-Mo-N( 1)--N(2) and N(OB)-MO-N(l)--N(2) are 53.6” and -37.3”, respectively. The pyrazole ring C (Fig. 1) is aligned approximately along the bisectral plane between rings E and F, whose interplanar angle of 117.3” is perhaps surprisingly the smallest of the three inter-planar angles with L*, viz. D to E 120.3” and D to F 120.5”.
6. 7. 8. 9.
10.
Il.
T. N. Briggs, C. J. Jones, J. Colquhoun, N. El Murr, J. A. McCleverty, B. D. Neaves, H. Adams and N. A. Bailey, J. Chem. Sot., Dalton Trans. 1985, 1249. J. A. McCleverty, Chem. Sot. Rev. 1983,12,331. S. L. W. McWhinnie, C. J. Jones, J. A. McCleverty, D. Collison and F. E. Mabbs, J. Chem. Sot., Chem. Commun. 1990,940. S. J. Reynolds, C. F. Smith, S. J. Jones and J. A. McCleverty, Znorg. Synth. 1985, 23, 4; S. Trofimenko, J. Am. Chem. Sot. 1967,89,3904; 1969,91, 588. A. C. T. North, D. C. Phillips and F. S. Mathews, Acta Cryst., Sect. A 1968, 24, 351. G. Sheldrick, Giittingen and Siemens plc (1990). N. J. Al Obaidi, C. J. Jones and J. A. McCleverty, J. Chem. Sot., Dalton Trans. 1990, 3329. B. Coe, C. J. Jones, J. A. McCleverty, S. L. W. McWhinme and F. McQuillan, work to be published. N. Al Obaidi, A. J. Edwards, C. J. Jones, J. A. McCleverty, B. D. Neaves, F. E. Mabbs and D. Collinson, J. Chem. Sot., Dalton Trans. 1989, 127. A. G. Orpen, L. Brammer, F. H. Allen, 0. Kennard, D. G. Watson and R. Taylor, J. Chem. Sot., Dalton Trans. 1989, Sl. M. T. Ashby and J. H. Enemark, J. Am. Chem. Sot. 1986, 108, 730 ; S. A. Roberts and J. H. Enemark, Acta Cryst., Sect. C 1989,45, 1292.
0277-5387/93 $6.OQ+ 40 Pergamon Press Ltd
1993
NEW’ PARAMAGNETIC PYRAZOLE COMPLEXES OF TRIS(3,5-DIMETHYLPYRAZOLYL)BORATO MOLYBDENUM NITROSYL CHLORIDE AND IODIDE AND THE STRUCTURE OF [Mo(NO){HB(3,5-Me2C$IN2)3)C1(3,5-Me&HN,H)] ANDRZEJ
WLODARCZYK
and STEFAN S. KUREK
Institute of Chemical Engineering and Physical Chemistry, Technical University of Krakow, 3 1- 155 Krakow, Poland and JOHN P. MAHER, ANDRE1 S. BATSANOV,? JUDITH and JON A. McCLEVERTYS
A. K. HOWARD?
School of Chemistry, University of Bristol, Cantocks Close, Bristol BS8 lTS, U.K. (Received 13 October 1992; accepted 2 December 1992)
Abstract-Reduction of [Mo(NO)L*Cl,] [L* = HB(3,5-Me,C,HN,),] with n-butyl lithium in the presence of SnBua3Cl afforded the paramagnetic (17-electron) [Mo(NO)L*C1(3,5Me,C3HN2H)] (1). Related compounds, [Mo(NO)L*XQ] (Q = pyrazole, 3,5-dimethylpyrazole, 4-bromopyrazole and 4-bromo-3,5_dimethylpyrazole ; X = Cl or I), were prepared by the reduction of [Mo(NO)L*X,] by Q (X = I) or by n-butyl lithium in the presence of Q (X = Cl). IR and EPR spectroscopic characterization of these species is reported and the Xray structure of [Mo(NO)L*C1(3,5-Me2C3HN2H)] - 1/2CHzC12, in which the molybdenum atom has octahedral coordination with disordered Cl and NO ligands, is described.
In an attempt to functionalize the pyrazolyl rings of the tris(3,5-dimethylpyrazolyl)borato ligand HB(3,5-Me2C3HN,)3 (L*) at the 4-positions we have investigated the reactions of [Mo(NO)L*Cl,] with LiBu” and SnBu”,Cl, our intention being to introduce the SnBu”, group onto at least one pyrazole ring in the coordinated tripodal ligand. In previous studies of the reactions of [Mo(NO)L*I,] with organo-lithium reagents we had observed that the reduction of the metal complex rather than displacement of I- by a carbanion was the dominant reaction. ’ This we could rationalize in terms of the reducing nature of the lithium organyl and the particularly accessible reduction potential of the molybdenum di-iodide (+0.33 V vs S.C.E. in CH3CN)
and also in terms of the apparent steric difficulty in generating a potential four-centred intermediate or transition state necessary to effect interchange of I by an organic group at the metal in the hindered {Mo(NO)L*I) entity. Indeed, treatment of No (NO)L*I,] with tolyl lithium in ether afforded [Mo(NO)L*12Li(OEt2)~], which contains the paramagnetic [Mo(NO)L*I,]- centre stabilized by the {Li(OEtz)Z}+ fragment. However, the reduction potential of [Mo(NO)L*Cl,] is significantly more anodic (-0.01 V vs S.C.E. in CH$N) than that of its iodo-analogue, and we reasoned that, because of this and the well-understood steric protection afforded by L* at the MO centre,’ reactivity might be diverted preferentially to the pyrazolyl rings of L*. In this paper we describe the reactions of [MO TPresent address : Department of Chemistry, Uni- (NO)L*X,] (X = Cl or I) with n-butyl lithium and versity of Durham, South Road, Durham DHl 3LE, SnBu”,Cl, in which partial decomposition of the U.K. nitrosyl complex with disruption of the tris(pyrazo$ Author to whom correspondence should be addressed. 1yl)borato ligand and reduction of the basic halide 715
716
A. WLODARCZYK
system occurred, and we report on the consequent formation of the paramqgnetic 3,5-dimethylpyrazole complex Flo(NO)L*X(3,5-Me,C,HN,H)] (1). Using reductive proceduq’es we have also prepared related complexes contairjing pyrazole (C3H3N2H), 4-bromo-(4-BrC3H2N2H) and 4-bromo-3,5dimethylpyrazole (3,5- eZ-4-BrC3N2H). These paramagnetic pyrazole l\r~complexes are closely related to the pyridine an 4,4’-bipyridyl complexes [Mo(NO)L*Cl(py)] and1 [Mo(NO)L*Cl(NCSH4 -C,H,N)], which have1 been briefly described elsewhere. 3 EXPERIMENTAL Synthetic studies
All reactions werecarrie out in an atmosphere of dry nitrogen. Toluene was redistilled from sodium benzophenone before use. o(NO)L*Cl,] was prepared as described elsew & re,4 butyl lithium was used as a 1.6 M solutio$ in hexane and other reagents were used as r ived. Column chromatography was carried !ce ut using 70-230 mesh silica gel. IR spectra were] recorded in KBr discs using a PE 1600 FTIR pectrometer and EPR spectra were recorded in \ ichloromethane using a Bruker ESP 300E instrunient.
General procedure for the ‘synthesis of [Mo(NO) L*IQ] (Q = C3H3N2H, 4- rC3HN2H, 3,5-Me& i H2H and 3,5-Me,-4-BrC,NhH)
A solution of [Mo(NO)LV,] (0.3 g) and pyrazole (0.09 g) or substituted pyra ole (1: 2 mole ratio) in toluene (30 cm’) was stirre at 80-90°C for 15-60 min, depending on the kind of pyrazole. The solution became deep green nd the solvent was removed in vacua, the resi ue being redissolved in dichloromethane. The s1 lution was chromatographed on silica gel, usin dichloromethane as een fraction was colan eluant, and the main lected. The solvent was evap rated and the residue recrystallized from dichl romethane/petroleum ether (b.p. 40--6O”C), affordi :; g green crystals. The yields were variable (30-50%). General procedure for the s nthesis of [Mo(NO) L*ClQ] (Q = C3H3N2H and t” 3,5-Me2C3HN2H] A solution of [Mo(NO)L Cl*] (0.3 g) and the appropriate pyrazole (2 mo 1es per mole of molybdenum complex) was wa ed to facilitate discomplex and then solution of the cooled to ca 60°C. Butyl lithi in hexane (0.8 cm3)
et al.
was added and the reaction mixture stirred for 1 h, during which time the solution became grey-green in colour. Petroleum ether (b.p. 40-6O”C) was added to precipitate salts and the solution was filtered, evaporated to dryness in vucuo and redissolved in the minimum volume of dichloromethane. The product was then obtained in the same way as the corresponding iodo complex and was isolated as green crystals (yields variable, 25-35%). Crystal strucfure determination of [Mo(NO)L*Cl
W-Me2C3HNzHll(1) A suitable crystal of the compound (a green plate sized 0.25 x 0.35 x 0.40 mm) was grown from dichloromethane/petroleum ether (b.p. 60-SO’C). Crystal data. Cz,,H30N90BC1Mo * 1/2CHzC12, M = 597.2, monoclinic, space group C2/c, a = 20.625(5), b = 10.858(2), c = 24.413(6) A, p’ = 96.23(2)“, U = 5.435(2) w3, Z = 8, D, = 1.46 g cm- 3, F(OO0) = 2.448, graphite-monochromated MO-K, radiation, R = 0.71069 A, p = 7.1 cm-‘. A total of 4000 independent reflections with 20 -=z47” were collected in the Wyckoff (limited w) scan mode. The reflection intensities were corrected for absorption, using the semi-empirical method,’ based on 396 azimuthal scans of 11 reflections (min. and max. transmission coefficients 0.5524 and 0.5744, respectively). The structure was solved by Patterson and Fourier methods and refined by fullmatrix least-squares using SHELXTLPLUS6 programs. Difference-Fourier maps revealed a disorder in the coordination sphere of the molybdenum atom, the Cl and NO ligands mixing at each site. Their occupancy factors were refined, yielding 0.65(2) for positions A and 0.35(2) for B (of both ligands). In the final refinement these atoms were treated in isotropic approximation, while all other non-hydrogen atoms were refined with anisotropic displacement parameters. Most of the hydrogen atoms were revealed by difference-Fourier syntheses, but all of them were included in the refinement in riding model in idealized positions, with the distances C-H 0.96, N-H 0.90 and B-H (from Fourier map) 1.07 A. The refinement of 310 variables converged at R = 0.041 and R’ = 0.052 for 3298 reflections with I > 2a(0 The weighting scheme w- ’ = 02(F) + 0.002F2 was used ; goodness of fit was 2.22. The maximum and minimum residuals in the final AF map were 0.56 and - 0.42 e A- 3 (around the disordered atoms). Selected bond lengths and angles are given in Table 1. Additional data (atom coordinates, thermal parameters and remaining bond lengths and angles) are available from the Cambridge Crystallo&aphic Data Centre.
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Structure of [Mo(NO)(HB(3,5-Me,C,HN&jCl(3,5-Me,C,HNzH)] Table 1. Selected bond lengths (A) and angles (“) Mo-Cl(lA) Mo-N(OA) MO-N( 1) MO-N(21) N(OA)--O(lA) N(l)--N(2) N(2)-C(3) C(3)--c(6) C(5)_C(7) N(ll)--C(U) N(12)--B C(13)-C(16) CU5Fw7) N(21)--C(25) N(22)-B C(23)--c(26) C(25)-C(27) N(3 lFC(35) N(32)-B C(33)--c(36) C(35)--c(37)
2.420(4) 1.782(12) 2.199(4) 2.217(4) 1.127(18) 1.359(6) 1.343(6) 1.498(8) 1.494(8) 1.333(6) 1.529(7) 1.495(8) 1.477(8) 1.342(6) 1.541(7) 1.497(8) 1.486(7) 1.342(6) 1.531(7) 1.493(8) 1.474(8)
Cl(lB)--MO-N(OB) Cl( lB)-Mo-N( 1) N(OB)-MO--N(~) Cl(lB)--MC+-N(ll) N(OB)-MO-N(l 1) Cl(lA)-MC+N(21) N(OA)--Mo-N(21) N(l)--MO-N(21) Cl(lA)-Mo-N(31) N(OA)--MO-N(3 1) N(l)-MO-N(31) N(21)--MO-N(31)
91.4(5) 91.9(2) 91.6(6) 95.3(2) 91.4(6) 91.1(l) 175.5(3) 87.6(l) 174.8(l) 91.5(3) 92.7( 1) 84.1(l)
RESULTS AND DISCUSSION
Synthetic and spectral studies On addition of n-butyl lithium to lJvlo(NO)L*Cl,] partially
dissolved
in toluene,
in a mole ratio of
2 : 1, a red colour developed, but further addition of
LiBu” was necessary to complete dissolution of the molybdenum chloride and generate a homogeneous deep red solution. On addition of SnBu”,Cl the solution darkened and on work-up, which involved chromatography over silica, paramagnetic 1 was formed as green crystals. This species was characterized by elemental analysis (Table 2) and by IR and EPR spectroscopy. The yield of the species was of the order 20% and it is clear that the generation of this 17-electron 3,5-dimethylpyrazole species must occur via decomposition of the starting
Mo-CI(lB) MO-N(OB) Mo-N( 11) MO-N(3 1) N(OBF-WB) N(1 k-C(5) C(3)_C(4) C(4)--c(5) N(ll)--N(12) N02k-w3) C(l3I--w4) C(14Fw5) N(21)--N(22) N(22wx23) C(23FJ24) C(24>--c(25) N(31)-N(32) N(32)-C(33) C(33)-C(34) C(34wx35) c1(10)--C(10)
2.423(9) 1.797(22) 2.162(4) 2.204(4) 1.199(34) 1.335(6) 1.349(7) 1.390(7) I .374(6) 1.357(6) 1.361(9) 1.376(8) 1.375(5) 1.346(6) 1.382(8) 1.381(7) 1.385(5) 1.356(6) 1.360(7) 1.391(7) 1.680(g)
Cl( 1A)--MO-N(OA) Cl( 1A)--MO-N( 1) N(OA)-Mo-N(1) Cl( 1A)-MO-N( 11) N(OA)-M+-N( 11) N(l)--MO-N(ll) CI(IB)-MO-N(21) N(OB)--MO-N(21) N( 1I)-Mo-N(21) Cl(lB)--MO-N(31) N(OB)--MO-N(31) N(ll)-MO-N(31) MO-N(OA)--O( 1A)
93.3(3) 89.2( 1) 91.5(3) 93.6(l) 95.7(3) 172.1(l) 175.0(2) 93.5(5) 84.9( 1) 90.9(2) 175.0(6) 84.0( 1) 178.2(8)
material, possibly via the reduced, 17-electron species [Mo(NO)L*Cl,]-. Furthermore, we had also previously observed that in reaction of [MO (NO)L*I,] with oxacyclohexane7 reduction of the molybdenum species and formation of the 3,5_dimethylpyrazole adduct, [Mo(NO)L*I(3,5Me2C3HN2H)], occurred. In a similar reaction with [Mo(NO)L*I,] 1 was again formed, probably because of the inclusion of SnBu*&l in the reaction mixture. We have observed on numerous occasions that iodine may be replaced by chlorine in reaction systems derived from [Mo(NO)L*I,] in the presence of chlorinated hydrocarbons.’ The yield of the pyrazole complexes was ca 20%. In a modification of the route to these 17-electron heterocycle complexes [Mo(NO)L*Cl,] was reduced by LiBu” in the presence of a suitable
718
A. WLODARCZYK et al. Table 2. Elemental analytical data and NO stretching frequencies for [Mo(NO)L*XQ]
Compound [Mo(NO)L*CI(Mq,C,HN,H)] [Mo(NO)L*Cl(C,@,N,H)I [Mo(NO)L*I(Me&HN,H)] [Mo(NO)L*I(C,H f N,H)] [Mo(NO)L*I(BrC H2N2H)] [Mo(NO)L*I(Me, rC,N,H)]
C
Found H
N
IR WO) (cm- ‘)
42.9 41.2 36.2 36.3 31.3 33.5
5.9 5.1 4.9 4.7 3.8 4.2
21.7 23.8 19.5 20.3 18.7 17.8
1610 1610 1617 1616 1618 1617
Calculated C H N 43.3 41.0 37.2 35.0 31.0 33.1
5.4 5.0 4.7 4.2 3.6 4.0
pyrazole Q (C3H3N2H, 3,5-MezC3HN2H, 4-BrC3H2 N,H), the desired comple b([Mo(NO)L*CIQ] being isolated in yields varying from 25 to 35%. However, [Mo(NO)L*12] react d directly with the pyrazoles Q (C3H3N2H, 3,5- t e2C3HN2H, 4-BrC3H2 N2H and 4-Br-3,5-Me,C,HzH), without the necessity of the lithium organylb affording modest yields of the 17-electron [Mo(Nb)L*IQ]. This last reaction may be compared 4th our earlier observations’ that the di-iodide reacted with an excess of pyrazole Q (C3H3NZH, 3,$-Me2C3HN2H), affording the cutionic 17-electron species lMo(NO)L*Qd+. The IR spectra of the ne compounds are entirely consistent with our form lations. In addition to exhibiting the normal stre hing modes associated with L* [e.g. v(BH) at ca 2,50 cm-‘] they show an i NO stretching frequency ip the range 1610-1618 - I, which is broadly co parable to the position rzthe related pyridine speci, 1 s [Mo(NO)L*C~(~~)J,~ but significantly lower than the corresponding bis(pyrazole) species [Mo(NO)L*Q,]+,~ as would be expected on the grounds of the nature of the ligands and positive charge. The complexes [Mo( O)L*XQ] (X = Cl, Q= C3H3N2H and 3,5- e$,HN,H; X = I, Q = C3H3N2H) exhibit EP spectra (Table 3) conc taining a signal at giw close to 1.976, with additional hyperfine coupling, A,,, of da 46 x 1O-4 cm- *, due to the I= 512 isotopes [95Mo (15.9%) and 97Mo (9.6%)]. These spectral par meters are similar to those obtained from [Mo(N )L*Cl(py)] (giso 1.970, d A,,, 45.7 x lop4 cm- ‘)’ and [Mo(NO)L*(pyrazole)$ (giiso 1.973-1.977, iAM043.8-46.0 X 10B4 cm- I). 9 The data are broad1 consistent with localization of the unpaired electr n on the metal centre. However, the EPR spectr4 m of [Mo(NO)L*I (3,5-Me,C3HN2H)] shows gi = 2.0036 and A,,. = 43.2 x 1O-4 cm- ‘, which di rs significantly from the other three species. We h ve no simple explanation for this observation, f, t it may arise from some form of distortion in the molecule.
22.7 23.9 19.5 20.4 18.1 17.4
Crystal structure of [Mo(NO)L*C1(3,5-Me2C3HN2
WI (1) The asymmetric unit of the structure contains one molecule of 1 in a general position and half of a CH$l, molecule, whose carbon atom is situated on a two-fold axis, thus corresponding to the stoichiometry [Mo(NO)L*C1(3,5-Me$,HN,H)] 1/2CHzC12. The molybdenum atom has distorted octahedral coordination, with one chlorine and five nitrogen atoms. The disorder (mixing) of Cl and NO ligands can be explained in terms of both R and S enantiomers of 1 occupying statistically the same crystallographic position (the crystal itself being centrosymmetric and racemic). The Mo-N bond lengths associated with the tris(pyrazolyl)borate and the 3,5_dimethylpyrazole ligands are similar (average 2.20 A) and reveal little difference in tram influence due to the Cl and NO groups (this also being a result of the nature of the disorder). As expected the Mo-N-O bond angle is essentially linear and the MO-N(O) distance (mean 1.79 A) is close to the usual (1.76-1.80 A).” In nitrosyl complexes of molybdenum with filled dxz and d,, orbitals, other ligands having filled pnorbitals or lone electron pairs tend to adopt the orientation with these orbitals approximately
Table 3. EPR spectral data obtained from [Mo(NO)L*
XQI A,,. x IO4 X
Q
Cl Cl I I
CxH,NzH 3,5-Me,C,HN2H CxHsNzH 3,5-Me2C,HNzH ..
.
Sk0
(cm- ‘)
1.9768 1.9768 1.9760 2.0036
46.2 46.1 45.34 43.22
Structure of [Mo(NO){HB(3,5-Me,C,HN&}C1(3,5-Me,C,HN,H)]
719
The only active hydrogen atom, at N(2), does not participate in hydrogen bonding. Acknowledgements-We are grateful to the British Council, through a Tripartite Acciones Integradas Programme, for partial support of this work (S.K. and A.W.), to the Politechnika Krakowska, Poland, for leave of absence (S.K. and A. W.), to the Royal Society for a Visiting Fellowship (A.S.B.) and to the SERC for financial assistance (EPR spectrometer). REFERENCES
J.
Fig. 1. Molecular structure of [Mo(NO)L*C1(3,5Me2C3HN2H] (1). For clarity, only the major (A) positions of Cl and NO ligands are shown (in B positions these ligands are interconverted), and all methyl hydrogens are omitted.
4.
5.
orthogonal to the NO group, thereby maximizing is the d,,-p overlap. ” In 1 such an orientation impossible due to the steric hindrance imposed by the methyl substituents of the pyrazolyl rings ; torsion angles N(OA)-Mo-N( 1)--N(2) and N(OB)-MO-N(l)--N(2) are 53.6” and -37.3”, respectively. The pyrazole ring C (Fig. 1) is aligned approximately along the bisectral plane between rings E and F, whose interplanar angle of 117.3” is perhaps surprisingly the smallest of the three inter-planar angles with L*, viz. D to E 120.3” and D to F 120.5”.
6. 7. 8. 9.
10.
Il.
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