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Synthesis and X-ray crystal structures of imido and isodiazene complexes of vanadium, niobium and tantalum
Polyhedron Vol. 16, No. 7, pp. 1081 1088, 1997
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Pergamon PII : S0277-5387(96)00387-7
Copyright ',~" 1997 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0277 5387,97 $17.00+0.00
Synthesis and X-ray crystal structures of imido and isodiazene complexes of vanadium, niobium and tantalum Andreas A. Danopoulos, ~ Robyn S. Hay-Motherwell, ~ Geoffrey Wilkinson,@ Tracy K. N. Sweet b and Michael B. Hursthouse b* ~'Johnson Matthey Laboratory, Chemistry Department, Imperial College, London SW7 2AY. U.K. bDepartment of Chemistry, University of Wales, Cardiff, PO Box 912, Cardiff CF1 3TB, U.K.
(Received 23 July 1996; accepted 6 August 1996)
Abstract--Interaction of [M(NBut)(NHBu')(H2NBut)C12]2, M = Nb, Ta, with five equiv, of ButNHLi gave {[M(NBu')3(NHBut)]Li2}2, M = Nb (2a), M = Ta (2b), which showed the presence of three different tertbutylimido groups and resisted further metallation. Interaction of MCIs, M = Nb, Ta, with 1-amino-2,2,6,6tetramethylpiperidine, CgHIsNNH2, in the presence of Me3SiC1-Et3N gave (Et3NH)[M(CgHI8N2)2CI4] , M = Nb (3a), M = Ta (3b). A similar interaction with NH4VO 3 gave low yields of [(CgHIsN2)2(OSiMe3)2 V(/t-O)V(O)(OsiMe3)2] (4). The X-ray crystal structures of (2a), (3b) and (4) have been determined. Copyright ~ 1997 Elsevier Science Ltd
Kevu'ords: imido complexes ; isodiazene complexes ; vanadium ; niobium ; tantalum ; crystal structures.
Anionic homoleptic tert-butylimido complexes M(NBu~)4Li2, M = Mo, W [la], Cr [lb], Re(NBut)4 Li(tmed) [lc] and Mn(NBut)4Li2(dme)2 [ld] were prepared by deprotonation of the complexes M(NBu~)2(NHBu')2, M = Cr, Mo, W, Re(NBut)3 (NHBu') and interaction of Mn(NBut)3CI with LiNHBu ~ under specific conditions. This paper describes attempts to prepare homoleptic tert-butylimido complexes of niobium and tantalum. Isodiazene complexes of tungsten and rhenium using the bulky hydrazine, 1-amino-2,2,6,6-tetramethylpiperidine, have been structurally characterized [2]. The extension of this chemistry to group 5 metals is also described.
RESULTS AND DISCUSSION
tert-But.vlimido complexes From the range of known tert-butylimido complexes of niobium and tantalum [3], [M(NBu t)
* Author to whom correspondence should be addressed.
(NHBut)(H2NBut)C12]z, M = Nb (la), M = Ta (lb), seemed to be good starting materials for the synthesis of imido-amido complexes, which in turn could be deprotonated to anionic imido complexes by strongly basic alkyl lithiums. Interaction of la or lb with 6 equiv, of LiNHBu ~in diethyl ether gave, after workup, oils, the ~H N M R of which consisted of one broad and one sharp tert-butyl peaks in approximate ratio 3 : 1. Although a plausible formulation for these oils is M(NBu t) e.g. (NHBut)3 (M = Nb, Ta), which is supported by their reactivity with LiNHBu ~ (see below), no attempt at further characterization was undertaken. Interaction of the dimers la or lb with l0 equiv, of Bu'NHLi in ether gave, after work-up, good yields of {[M(NBut)3(NHBut)]Li21: M = Nb (2a); M = Ta (2b), as colourless, extremely airsensitive prisms. Compounds 2a and 2b could also be obtained, but in lower yields, by reactions of the above mentioned oils with 3 equiv, of ButNHLi. It is worth noting that neither higher (BffNHLi) : 1 ratios, nor interaction of 2a or 2b with BunLi or MeLi, resulted in deprotonation of the remaining tert-butylamido group. An analogous situation was observed by Wigley [4] who reported the preparation of [Li(thf)2][M (Nmesh (NHmes)] M = Nb, Ta, rues = 2,4,6-trimethylphenyl.
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A. A. Danopoulos et al.
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(1R, NMR) behaviour. The f i N - - H ) in the IR ~s at 3175 cm-1, while in the tH N M R spectrum there are four inequivalent tert-butyl groups in the ratio 1 : 1 : 1 : 1. These are assigned to one linear tert-butylimido, one tert-butylamido and two tert-butylimido groups associated with lithium atoms. The chemical inequivalence of these four groups is consistent with an arrangement in which one lithium atom is bridging two imido groups, while the other is bridging one imido and one amido groups. Each lithium site connects the two NbN4 tetrahedra by association with three nitrogen atoms, therefore, each cation is bound to two bridging imido nitrogen atoms and one amido nitrogen atom. This is further supported by the presence of two inequivalent lithium environments in the 7Li NMR spectrum. Compounds 2a and 2b reacted with C6HsSeBr in petroleum to give low yields of oily products which were characterized by EI mass spectra as (Bu'N)M(NHBut)(Bu*NSePh)2, M = N b , Ta, but crystalline compounds could not be obtained. Similar compounds have been obtained by interaction of W(NBut)4Li: with C~,HsSC1 [6].
The crystal structure of 2a has been determined by X-ray diffraction and is shown in Fig. 1; selected bond lengths and angles are in Table 1. There are two crystallographically independent centrosymmetric dimers in each of which two Nb(NBut)3(NHBut) units are linked by N . . . L i . . . N bridges. The four lithium cations of each dimer exhibit positional disorder and fractionally occupy six sites in the form of a cyclohexane-type ring (Fig. 1). A similar situation was observed in the related dimer [Wz(NBut)sLi4] [5]. In the present case the amido function is presumed to be contained within the bridging system, since the terminal ligand is a normal, linear 6e tert-butylimido. The two imido groups on each niobium which are involved in the bridging are bent, presumably as a result both of the lithium coordination and the over availability of g-electrons for an t8e niobium count. Whilst there may be some disorder of the three bridged ligands, linked to the disorder of the lithiums, it would seem that the amide predominantly occupies the N(n4) site, which has the longest bond and the smallest N b - - N - - C angle. The amide protons were not, however, located on a difference map. The lithium cations can formally be considered as four-coordinate. Three sites are occupied by nitrogen atoms with L i . . . N interactions ranging between 1.92(3) and 2.20(3) A, and the fourth site taken up by an "agostic" interaction with a methyl group, with L i . . . C distances ranging from 2.50(2) to 2.66(2) A. Compounds 2a and 2b show identical spectroscopic
Isodiazene complexes In a previous paper [2] we reported on the interaction of 1-amino-2,2,6,6-tetramethylpiperidine with tungsten and rhenium oxo-complexes to obtain corn-
N(11') Li(11')
~.~"Li(12)
N(14')
~
.~
(13')
s
N(12)
i
N(12')
N(13~.'~.
Nil4)
.
~
'"
~
~
Li(12') /S
Li(11)
N(ll) Fig. 1. A representation of the {[Nb(NBu~)3(NHBut)]Li2}2dimer (2a), showing all lithium sites (2/3 occupied). The Bu' carbon atoms have been omitted for clarity.
Complexes of vanadium, niobium and tantalum Table 1. Selected bond lengths (A) and angles (°) for {[Nb(NBu')3(NHBu')]Li2}2 (2a) with e.s.d.s in parentheses n=l
n=2
Nb(n)--N(nl) Nb(n)--N(n2) Nb(n)--N(n3) Nb(n)--N(n4) N(nl)--C(nl) N(n2)--C(n2) N(n3)--C(n3) N(n4)--C(n4)
1.810(6) 1.980(7) 2.000(7) 2.023(6) 1.447(10) 1.486(9) 1.500(10) 1.494(11)
1.782(6) 1.949(6) 2.011 (7) 2.029(7) 1.489(9) 1.485(9) 1.522(10) 1.478(10)
N(nl)--Nb(n)--N(n2) N(nl)--Nb(n)--N(n3) N(nl)--Nb(n)--N(n4) N(n2)--Nb(n)--N(n3) N(n2)--Nb(n)--N(n4) N(n3)--Nb(n)--N(n4) Nb(n)--N(nl)--C(nl) Nb(n)--N(n2)--C(n2) Nb(n)--N(n3)--C(n3) Nb(n)--N(n4)--C(n4) N(n2')--Li(nl)--N(n3) N(n2')--Li(nl)--N(n4) N(n3)--Li(nl)--N(n4) N(n3")--Li(nl)--N(n4) N{n4)--Li(nl )--N(n2) N(n3")--Li(nl)--N(n2) N(n3)--Li(n2)--N(n4') N(n3)--Li(n2)--N(n2)
117.9(2) 114.5(3) 116.1(3) 102.3(3) 102.3(3) 101.5(2) 175.5(5) 138.2(5) 133.4(6) 130.1(5) 116.8(11) 115.6(10) 96.7(8) --
115.9(3) 116.5(3) 115.8(3) 103.0(3) 103.0(3) 100.5(3) 177.3(6) 135.0(5) 132.2(5) 132.1(5) ---114.0(12) 92.8(9) 115.3(12) ---
N (n4')--Li (n2)--N (n2) N(n2")--Li(n2)--N(n3) N(n2")--Li(n2)--N(n4) N(n3)--Li(n2)--N(n4) N(n3')--Li(n3)--N(n2) N(n3')--Li(n3)--N(n4) N(n2)--Li(n3)--N(n4) N(n4")--Li(n3)--N(n3) N(n4")--Li(n3)--N(n2)
N (n2)--Li (n3)--N (n3)
---
112.6(10) 93.7(11) 111.0(12) ----
117.4(14) 116.7(12) 92.8(10) ---
--
117.4(12) 114.5(11) 92.1 (8) ---111.7(12) 114.4(11) 94.7(10)
Where n = 1 (molecule 1) or 2 (molecule 2) ; ' represents the symmetry transformation - x + 1, - y , - z + 1 ; " represents the symmetry transformation - x + 2, - y + 1, - z.
pounds which, on the grounds of structural data and oxidation state arguments, were classified as isodiazene complexes rather than hydrazido ( 2 ) species. Extension of this chemistry to group 5 metals led to isolation of anionic complexes (EtaNH)[M(N2C 9 H~8)2C14] (3a), M = N b ; (3b) M = T a . They were prepared in satisfactory yields in benzene from MCl5 (M = Nb, Ta) in the presence of EtaN/Me3 SiCl, which is thought to form in situ trimethylsilylhydrazine. They were crystallized from toluene as toluene solvates, which prevented informative and reproducible combustion analyses due to solvent loss. The structure of 3b was determined by X-ray crystallography and is shown in Fig. 2; selected bond lengths and angles are in Table 2. The tantalum centre
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has distorted octahedral geometry with cis-C9H~sN2 groups. Close intermolecular contacts are found between the octahedral face defined by C1(2), C1(3) and C1(4) and the triethylammonium cation [ N ( 3 ) . . . C I distances range between 3.40(1) and 3.46(1) A]. The T a - - N - - N unit is nearly linear [176.5(5) and 176.4(5)°], while the exo nitrogen atoms N(11) and N(21) are planar [angle sum 357.5(2) and 357.2(2) °, respectively]. Their planes are approximately aligned with the meridional planes of the octahedron [i.e. plane of N(11) with that defined by N(1), Ta, CI(1), C1(3) and of N(21) with that defined by N(2), Ta, CI(1) and C1(3)]. There are two types of T a - - C I distances, the longest being trans to the N ligands, indicative of a certain degree of trans influence exerted by the C9HjsN2 group. The T a - - N distances [1.865(7) and 1.882(6) A] and the N - - N distances [1.283(9) and 1.259(8) A] are both within the range between single and double bonds. Thus, metrical data of the T a - - N - - N moiety strongly support the presence of extensive n-interaction delocalized over the metal and nitrogen atoms. Various resonance forms have been invoked to describe the bonding in compounds of type MN2R4 [2], e.g. M ~- N ~ - + N R 2 M~N--NR2
M --]~+NR
2
M ~-+N--NR2
making the unambiguous assignment of formal metal oxidation states difficult. The two extreme models of hydrazido (2-) and isodiazene (0) have been encountered in the literature [2]. In the present case an isodiazene formulation is preferred, since it gives a realistic oxidation state of (Ill) for the tantalum. In support of this is the observation of Ta--CI(1) and Ya--Cl(3) distances [2.451 (2) and 2.472(2)/k], which are longer than those reported for the tantalum(V) compounds [7] [2.317(2)-2.362(2) A]. The diamagnetism of 3b may be ascribed to pairing of the two d-electrons occupying the lowest energy single orbital resulting from n-perturbation because of the isodiazene ligands. The identical 1H N M R spectra of 3a and 3b suggest that they are isostructural. Interaction of NH4VO3 with H2NNCgHI8 in neat Me3SiC1/Et3N (see Experimental) gave crystals of [(C9H,sN2)2(OSiMe3)2V(/~-O)V(O) (OSiMe3)2] (4). This could not be obtained free of siloxanes even after repeated recrystallizations from petroleum. The structure was unequivocally determined by Xray crystallography and is shown in Fig. 3 ; selected bond lengths and angles are in Table 3. It is an asymmetric oxo-bridged dimer. The coordination geometry at V(1) can be best described as trigonal bypyramidal, the axial sites are occupied by one CgH18N2 ligand and the bridging oxo atom, while an additional CgH~sN2 and two OSiMe3 groups are in the equatorial position [coordination angles: N(1)--V(1)---O(I) = 171.97(11) '~, the angles in the equatorial plane range between 117.68(12) and 120.22(11)]. The coord-
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A . A . Danopoulos et al. C(22) C(21 l) C(23) C(212)
C(112)
C(24) C(12)
o(1) C(ll) N(ll) N(1)
C(13)
C(252)
C(lll
c(251) C(14) C(151 C1(4)
c(15"~)
c1(2) c1(3)
Fig. 2. The structure of the [Ta(C9H~sN2):CI4] anion of 3b.
Table 2. Selected bond lengths (A) and (') for the [Ta(CgH~sN2)2CI4]- anion of 3b, with e.s.d.s in parentheses Ta--N(1) Ta--N(2) Ta--CI(1) Ta--CI(2) Ta--CI(3) Ta--CI(4) N(1)--N(ll) N(2)--N(21)
1.865(7) 1.882(6) 2.451 (2) 2.553(2) 2.472(2) 2.535(3) 1.283(9) 1.259(8)
CI(I)--Ta--CI(2) CI(I)--Ta--CI(3) CI( 1)--Ta--CI(4) CI(I)--Ta--N(I) CI(I)--Ta--N (2) CI(2)--Ta--CI(3) CI(2)--Ta--CI(4) CI(2)--Ta--N (1) CI(2)--Ta--N (2) CI(3)--Ta--CI(4) CI(3)--Ta--N(I) CI(3)--Ta--N (2) CI(4)--Ta--N(1) CI(4)--Ta--N(2) N(1)--Ta--N(2) Ta--N(I)--N(I 1) Ta--N (2)--N (21)
83.12(6) 163.64(7) 85.58(9) 96.3(2) 96.0(2) 84.23(6) 87.04(6) 91.2(2) 177.7(2) 83.44(9) 94.3(2) 96.2(2) 177.3(2) 90.8(2) 91.0(2) 176.5(5) 176.4(5)
short N - - N [1.285(3)-1.245(4) A], V - - N [1.725(2)1.781(3) A.] bonds and planar exo-nitrogen atoms [angle sums 356.6 and 359.9 ° around N ( l l ) and N(21), respectively], resemble those already discussed above for 3b, again pointing to an isodiazene as the best description of the nitrogen ligand. Of particular interest is the almost linear highly asymmetric oxo-bridge. In this V(2)--O(1) [1.650(2) /~] is only slightly longer than the terminal V(2)--O(6) [1.616(2) A] and is in contrast with the long W(1)--O (1) bond [2.175 (2) A,], the latter indicating weakening of the bond between V(1) and the bridging oxygen O(1). An explanation of this asymmetry could be found in the different electronic environment of the vanadium atoms: V(1), formally a V m centre, is nelectron rich and, therefore, is not involved in any n_ type interactions with the oxo-group. V(2) is more nacidic, resulting in strong vanadium-oxygen bonds. The slight difference in V--OSiMe3 distances between the two metal centres underlines the nature of siloxides as "spectator" ligands. The same compound could be obtained when using VOCI3, W205 or VOCI2(OSiMes) instead of NH4VO3 although purification was even more difficult. Replacement of the last oxo group from the vanadium proved impossible even after prolonged reaction times. EXPERIMENTAL
ination geometry at V(2) is distorted tetrahedral comprising two OSiMe3 groups, one terminal oxo and one bridging oxo atoms. The metrical data for the V - - N - - N moiety on V(1) observed here, e.g.
Analyses were by the Imperial College microanalytical laboratory. All operations were carried out under purified Ar or N2, or in a Vacuum Atmospheres
Complexes ofvanadium, niobium and tantalum
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C(152)
C(13)
C(28)
C(14)
C(112) C(12) C(26) C(151) N(11
~i(2) C(16) C(17)
C(lll) 0(2)
Si(l)
c(252)
C(251)
C(31) ~_ 0,(1) )C(18) s(21) ~
C(212){ C(211)
c(2D
O
(
6
)
0(4) ~ ] Si(3ff'~'==='=~
C(32)
c(24)
c(23)
C(22)
J%(5.,
(~
,)
C(41)
C(~)
C(42) Fig. 3. The structure of [(CgHlaN2)2(OSiMe3)2V(#-O)V(O)(OSiMe3)2] (4).
glove-box. All solvents were degassed and distilled before use. N M R data were obtained using a JEOL EX-270 or Bruker Avance DRX-300 spectrometer operating at 270 or 300 MHz (~H), respectively, and referenced to the residual proton impurity in the solvent (3 7.15 C6D6). Mass spectra were obtained on a VG-7070E or VG Autospec spectrometers. Commercial chemicals were from Aldrich and Avocado Chemicals. The following starting materials were prepared according to literature procedures: [Nb(NBu') (HNBut) (H2NBut)C12]2 [8], [Ta(NBut)(NHBu t) (H2NBut)C12]2 [8] H2NNCgHIs [9]. ButNHLi was obtained by interaction of BunLi with ButNH2 in hexanes. The petroleum used throughout had a boiling point of 40-60°C.
Dilithiumtris(tert-butylimido)(tert-butylamido) niobate(2a) To a solution of [(Bu t N)Nb(HNBu t )(H2NBu t )C1212 (0.76 g, 1 mmol) at - 7 8 ° C in Et20 (ca 50 cm 3) was added a suspension of ButNHLi [0.79 g, 10 mmol in
EhO (30 cm3)]. The mixture was allowed to warm to room temperature and stirred overnight. Evaporation of volatiles under reduced pressure, extraction of residue with hot petroleum (5 x 30 cm3), filtration and concentration of filtrate to ca 30 cm 3 and standing at room temperature overnight gave colourless prisms. Yield 0.55 g 70%; m.p. > 230°C (decomposition). X-ray quality crystals were obtained by slow cooling solutions in toluene. [Found (calc.) : C, 49.2 (49.1); H, 9.4 (9.4) ; N, 15.0 (14.3)%]. N M R (C6D6) : ~H: 6 2.6 (s, br, IH, NHCMe3), 1.83, 1.62, 1.59 (s, 9H each, NCMe3), 1.47 (s, 9H, NHCMe3). 7Li: 5 2.5 and 2.0.
Dilithiumtris(tert-butylimido)(tert-butylamido) tantalat e(2b) As for 2a, but from [(Bu'N)Ta(HNBu ~) (H2NBut)C12]2 (0.94 g, 1 mmol) and ButNHLi (0.79 g, 10 mmol). Yield 0.69 g, 75% ; m.p. > 230°C (decomposition). [Found (calc.) : C, 39.8 (40.0); H, 7.5 (7.7); N, 11.6 (11.7)%]. N M R (C6D6) ~H: ~ 2.6 (s, br, 1H, NHCMe3), 1.73, 1.49, 1.47 (s, 9H each, NCMe3), 1.37 (s, 9H, NHCMe3). 7Li: 6 2.5 and 2.0.
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A. A. Danopoulos et al.
Table 3. Selected bond lengths (A) and angles (°) for [(CgHIsN2)2(OSiMe3)2V(/~-O)V(O)(OSiMe3)]2 (4) with e.s.d.s in parentheses V(1)--N(1) V(I)--N(2) V(1)--O(I) V(1)--O(2) V(1)--O(3) V(2)--O(1) V(2)--O(4) V(2)~O(5) V(2)--O(6) Si(1)--O(2) Si(2)--O(3) Si(3)--O(4) Si(4)--O(5) N(I)--N(11) N(2)--N(21)
1.725(2) 1,781(3) 2.175(2) 1.827(2) 1.813(2) 1,650(2) 1.806(2) 1.810(2) 1,616(2) 1,626(2) 1.619(2) 1.633(2) 1.645(2) 1.285(3) 1.245(4)
N(I)--V(1)--N(2) N(1)--V(1)--O(1) N(1)--V(1)---O(2) N(1)--V(1)--O(3) N(2)--V(I)--O(1) N(2)--V(I)--O(2) N(2)--V(1)--0(3) O(1)--V(1)--O(2) O(1)--V(1)--O(3) O(2)--V(1)--O(3) V(I)--N(1)--N(I 1) V(I)--N(2)--N(21) V(I)--O(I)--V(2) V(1)--O(2)--Si(1) V(1)--O(3)--Si(2) O (1)--V(2)--O(4) O(1)--V(2)--O(5) O ( 1)--V (2)--O (6) O(4)--V(2)--O(5) O(4)--V(2)--O(6) O(5)--V(2)--O(6) V(2)--O(4)--Si(3) V(2)--O(5)--Si(4)
91.86(12) 171.97(! 1) 96.72(11) 98.91(12) 80.32(10) 117.68(12) 119.00(12) 85.42(9) 86.59(9) 120.22(11) 176.4(2) 174.3(2) 162.93(13) 142.11(14) 162.89(14) 111.07(11) 110.42(11) 109.64(12) 108.46(11) 110.34(11) 106.81(11) 148.00(14) 128.22(13)
( T r i e t h y l a m m o n i u m ) [tetrachlorobis(2,2,6,6-tetrarnethylpiperid-l-ylnitrene)tantalate(lll) (3b) and niobate(Ill) (3a)
To TaC15 (0.3 g, 0.84 mmol) in benzene (10 cm 3) was added sequentially Et3N (0.58 g, 4.2 mmol), 1amino-2,2,6,6-tetramethylpiperidine (0.32 g, 2.1 mmol) then Me3SiCI (0.53 g, 4.2 mmol). The mixture was stirred and refluxed under N2 overnight. After cooling and removal of all volatiles in vacuo, the residue was washed with petroleum (20 cm 3) and extracted with toluene (2 x 30 cm3). After filtration, reduction of volume of toluene to ca 15 cm 3 and cooling to -20°C, orange-red crystals were obtained. Yield 0.36-0.48 g, 60-70%. Recrystallization from toluene yielded crystals of X-ray quality. The crystals
decomposed on drying in vacuo due to facile removal of toluene. Consequently, no satisfactory analytical results were obtained. ~H N M R of various samples showed the presence of toluene to varying concentrations. N M R (C6D6) ~H: 6 9.42 (s, br, 1H, Et3NH), 2.56 [pseudoquartet, br, 6H (CH3CH2)3NH ], 1.85 (s, 12H, Me4CsH6), 1.77 (s, 12H, Me4CsH6), 1.33 (m, 12H, Me4CsH6), 0.78 (t, br, 9H, (CH3CHz)3NH]. The corresponding niobium compound could be prepared in the same way with or without the presence of C6H6. However, toluene was lost more readily from the final crystalline material. N M R (C6D6) ~H : 6 9.42 (s, br, IH, Et3NH), 2.56 [pseudoquartet, br, 6H (CH3CH2)3NH], 1.85 (s, 12H, Me4CsH6), 1.77 (s, 12H, Me4CsH6), 1.33 (m, 12H, Me4CsH6), 0.78 [t, br, 9H, (CH3CH2)3NH]. [Bis(2,2,6,6-tetramethylpiperid- 1-ylnitrene)bis(trimethyl siloxo)]vanadium(la-oxo)[bis(trimethylsiloxo)oxo] vanadium (4)
This compound could be prepared using any of the following starting materials, VOCI3, NH4VO3, V205, VOCI2(OSiMe3) [prepared from VOC13 using (Me3Si)20 in the presence of Et3N and Me3SiC1] without benzene as solvent. NH4VO3 gave the cleanest product. To NH4VO3 (0.6 g, 6 mmol) was added sequentially with stirring, EtaN (8 g, 25 mmol), 1amino-2,2,6,6-tetramethylpiperidine (2.3 g, 15 mmol) then Me3SiCI (8 cm 3, 25 mmol) and the mixture refluxed overnight. After cooling the volatiles were removed under vacuum and the dark residue was extracted with petroleum (2 x 50 cm3). After concentration of extracts in vacuo to ca 5 cm 3 and cooling to -30°C, dark violet crystals were obtained. X-ray quality crystals were obtained after recrystallization from petroleum. Yield: 0.25 g, 20-30%. Repeated recrystallization from petroleum did not yield crystals of analytical purity due to contamination by siliconcontaining oils and starting piperidine, as proved by NMR. N M R (C6D6) IH: 6 1.47 (s, 12H, Me4CsH6), 1.01, 0.89, 0.86, 0.82 (each s, 6H, Me4CsH6), 0.35 (s, 18H, OSiMe3), 0.28 (s, 18H, OSiMe3). X-ray crystalloyraphy
X-ray data for compounds 2a, 3b and 4 were collected at low temperature (see Table 4) using a FAST TV area detector diffractometer with Mo-K~ radiation (2 = 0.71069 A), as previously described [10]. The structures were solved via direct methods procedures of SHELXS-86 [11], and refined by full-matrix leastsquares on F~0, using the program SHELXL-93 [12]. All unique data used were corrected for Lorentz polarization factors and for absorption using the program DIFABS [13], with maximum and minimum correction factors listed in Table 4. The non-hydrogen atoms were refined with anisotropic thermal parameters and the hydrogen atoms of 2a and 3b were
Complexes of vanadium, niobium and tantalum
1087
Table 4. Crystal data and structure refinement details for compounds 2a, 3b and 4 Compound Formula
2a
3b
C32H74LiaNsNb2
CIsH36CI4N4Ta •
Mr Crystal system Space group a (A) b (A) c (A.) ~(~') fl('') 7(') U (/~3) Z Dc (Mg m -3) F(000) Crystal size (mm) p(Mo-K,) (mm-z) Reflections collected Independent reflections (R~,,) Data, restraints, parameters Goodness of fit, F 2 Final R indices R~, wR:, [I> 2a(/)] R,, wR2 (all data) Largest differencepeak and hole (e A -3)
784.56 Triclinic PI 10.22(2) 13.92(2) 15.916(7) 92.26(13) 100.7(2) 90.81 (4) 2222(4) 2 1.173 824 0.18 × 0.18 × 0.15 0.499 9384 6117 (0.0718) 6112, 0, 465 1.035 0.0540, 0.1080 0.0923, 0.1196 0.753, -0.499
4 C5oH72N406Si4V2
C7H8"C6H,6N 825.59 Monoclinic P2~/c 10.198(8) 25.180(10) 15.292(10) 90 106.46(7) 90 3766(2) 4 1.456 1688 0.42 × 0.15 × 0.12 3.229 14662 5596 (0.0642) 5589, 0, 366 1.067 0.0504, 0.1215 0.0665, 0.1472 3.632, -0.885
799.16 Triclinic Pi 10.087(3) 12.597(4) 18.823(2) 70.65(I) 87.77(5) 87.20(2) 2253(I) 2 1.178 860 0.36 × 0.18 × 0.12 0.546 9619 6225 (0.0537) 6215, 0, 483 0.965 0.0421, 0.1016 0.0574, 0.1400 0.581, -0.342
S = [Z(w(Fo2-F:c):f(n-p))]'/:; R, = XI(Fo-F¢)]/XFo; wR2 = [Xw(H - H)~/Xw(Fo:):]'/: ; w = l/[,r:(H)+ (xP) 2+gP]; P = [max(F2) + 2(F~)]/3. Where n = number of reflections,p = total number of parameters, x = 0, 0.0716, 0.0527 and g = 0, 0, 0 for compounds 2a, 3b and 4, respectively.
included in idealised positions. Due to the uncertainties in positioning, hydrogen atoms on the Bu t methyl groups of I associated with the Li interactions were omitted. The methylene protons of 4 were experimentally located whilst the methyl hydrogen atoms were placed in calculated positions. The solvent of crystallization, toluene, within the lattice of 3b was shown to exhibit positional disorder. The carbon atoms were refined in split sites with partial occupancy factors and consequently hydrogen atoms were ignored in the refinement. All crystal data and refinement details are summarized in Table 4. Additional material available from the Cambridge Crystallographic Data Centre comprises fractional atomic co-ordinates, thermal parameters and remaining bond lengths and angles.
2.
3. 4. 5.
6.
7.
Acknowledyements--We thank the EPSRC for support (A.A.D. and R.S.H.-M.) and for provision of X-ray facilities. REFERENCES
8. 9.
1. Danopoulos, A. A., Wilkinson, G., HussainBates, B. and Hursthouse, M. B., (a) J. Chem. Soc., Dalton Trans. 1990, 2753 ; (b) Danopoulos, A. A. and Wilkinson, G., Polyhedron, 1990, 9,
10.
1009; (c) Danopoulos, A. A., Longley, C. J., Wilkinson, G., Hussain, B. and Hursthouse, M. B., Polyhedron, 1989, 8, 1767; (d) Danopoulos, A. A., Wilkinson, G., Sweet, T. K. N. and Hursthouse, M. B., J. Chem. Soc., Dalton Trans. 1994, 1037. Danopoulos, A. A., Wilkinson, G. and Williams, D. J., J. Chem. Soc., Dalton Trans. 1994, 907, and refs therein. Wigley, D. E., Pro9. Inory. Chem. 1994, 42, 239. Smith, D. P., Allen, K. D., Carducci, M. D. and Wigley, D. E., Inory. Chem. 1992, 31, 1319. Danopoulos, A. A., Wilkinson, G., Hussain, B. and Hursthouse, M. B., J. Chem. Soc., Chem. Commun. 1989, 896. Hankin, D. M., Danopoulos, A. A., Wilkinson, G., Sweet, T. K. N. and Hursthouse, M. B., J. Chem. Soc., Dalton Trans. 1996, 1309. (a) Cotton, F. A., Durag, S. A. and Roth, W. J., Acta Cryst. 1985, C41, 881; (b) Lavasseur, G. and Beauchamp, A. L., Acta Cryst. 1991, C47, 547, and refs therein. Bates, P. A., Nielson, A. J. and Waters, J. M., Polyhedron, 1985, 4, 1391. Hinsberg III, W. D., Schultz, P. G. and Dervan, P. B., J. Am. Chem. Soc. 1982, 104, 766. Danopoulos, A. A., Wilkinson, G., HussainBates, B. and Hursthouse, M. B., J. Chem. Soc., Dalton Trans. 1991, 1855.
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11. Sheldrick, G. M., SHELXS-86, Acta Cryst. 1990, A46,467. 12. Sheldrick, G. M., SHELXL-93, Program for Crystal Structure Refinement. University of G6ttingen, Germany, 1993.
13. Walker, N. P. C. and Stuart, D., Acta Cryst. 1983, A39, 158 adapted for FAST geometry by A. Karaulov, University of Wales, Cardiff, 1991.
~')
Pergamon PII : S0277-5387(96)00387-7
Copyright ',~" 1997 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0277 5387,97 $17.00+0.00
Synthesis and X-ray crystal structures of imido and isodiazene complexes of vanadium, niobium and tantalum Andreas A. Danopoulos, ~ Robyn S. Hay-Motherwell, ~ Geoffrey Wilkinson,@ Tracy K. N. Sweet b and Michael B. Hursthouse b* ~'Johnson Matthey Laboratory, Chemistry Department, Imperial College, London SW7 2AY. U.K. bDepartment of Chemistry, University of Wales, Cardiff, PO Box 912, Cardiff CF1 3TB, U.K.
(Received 23 July 1996; accepted 6 August 1996)
Abstract--Interaction of [M(NBut)(NHBu')(H2NBut)C12]2, M = Nb, Ta, with five equiv, of ButNHLi gave {[M(NBu')3(NHBut)]Li2}2, M = Nb (2a), M = Ta (2b), which showed the presence of three different tertbutylimido groups and resisted further metallation. Interaction of MCIs, M = Nb, Ta, with 1-amino-2,2,6,6tetramethylpiperidine, CgHIsNNH2, in the presence of Me3SiC1-Et3N gave (Et3NH)[M(CgHI8N2)2CI4] , M = Nb (3a), M = Ta (3b). A similar interaction with NH4VO 3 gave low yields of [(CgHIsN2)2(OSiMe3)2 V(/t-O)V(O)(OsiMe3)2] (4). The X-ray crystal structures of (2a), (3b) and (4) have been determined. Copyright ~ 1997 Elsevier Science Ltd
Kevu'ords: imido complexes ; isodiazene complexes ; vanadium ; niobium ; tantalum ; crystal structures.
Anionic homoleptic tert-butylimido complexes M(NBu~)4Li2, M = Mo, W [la], Cr [lb], Re(NBut)4 Li(tmed) [lc] and Mn(NBut)4Li2(dme)2 [ld] were prepared by deprotonation of the complexes M(NBu~)2(NHBu')2, M = Cr, Mo, W, Re(NBut)3 (NHBu') and interaction of Mn(NBut)3CI with LiNHBu ~ under specific conditions. This paper describes attempts to prepare homoleptic tert-butylimido complexes of niobium and tantalum. Isodiazene complexes of tungsten and rhenium using the bulky hydrazine, 1-amino-2,2,6,6-tetramethylpiperidine, have been structurally characterized [2]. The extension of this chemistry to group 5 metals is also described.
RESULTS AND DISCUSSION
tert-But.vlimido complexes From the range of known tert-butylimido complexes of niobium and tantalum [3], [M(NBu t)
* Author to whom correspondence should be addressed.
(NHBut)(H2NBut)C12]z, M = Nb (la), M = Ta (lb), seemed to be good starting materials for the synthesis of imido-amido complexes, which in turn could be deprotonated to anionic imido complexes by strongly basic alkyl lithiums. Interaction of la or lb with 6 equiv, of LiNHBu ~in diethyl ether gave, after workup, oils, the ~H N M R of which consisted of one broad and one sharp tert-butyl peaks in approximate ratio 3 : 1. Although a plausible formulation for these oils is M(NBu t) e.g. (NHBut)3 (M = Nb, Ta), which is supported by their reactivity with LiNHBu ~ (see below), no attempt at further characterization was undertaken. Interaction of the dimers la or lb with l0 equiv, of Bu'NHLi in ether gave, after work-up, good yields of {[M(NBut)3(NHBut)]Li21: M = Nb (2a); M = Ta (2b), as colourless, extremely airsensitive prisms. Compounds 2a and 2b could also be obtained, but in lower yields, by reactions of the above mentioned oils with 3 equiv, of ButNHLi. It is worth noting that neither higher (BffNHLi) : 1 ratios, nor interaction of 2a or 2b with BunLi or MeLi, resulted in deprotonation of the remaining tert-butylamido group. An analogous situation was observed by Wigley [4] who reported the preparation of [Li(thf)2][M (Nmesh (NHmes)] M = Nb, Ta, rues = 2,4,6-trimethylphenyl.
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A. A. Danopoulos et al.
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(1R, NMR) behaviour. The f i N - - H ) in the IR ~s at 3175 cm-1, while in the tH N M R spectrum there are four inequivalent tert-butyl groups in the ratio 1 : 1 : 1 : 1. These are assigned to one linear tert-butylimido, one tert-butylamido and two tert-butylimido groups associated with lithium atoms. The chemical inequivalence of these four groups is consistent with an arrangement in which one lithium atom is bridging two imido groups, while the other is bridging one imido and one amido groups. Each lithium site connects the two NbN4 tetrahedra by association with three nitrogen atoms, therefore, each cation is bound to two bridging imido nitrogen atoms and one amido nitrogen atom. This is further supported by the presence of two inequivalent lithium environments in the 7Li NMR spectrum. Compounds 2a and 2b reacted with C6HsSeBr in petroleum to give low yields of oily products which were characterized by EI mass spectra as (Bu'N)M(NHBut)(Bu*NSePh)2, M = N b , Ta, but crystalline compounds could not be obtained. Similar compounds have been obtained by interaction of W(NBut)4Li: with C~,HsSC1 [6].
The crystal structure of 2a has been determined by X-ray diffraction and is shown in Fig. 1; selected bond lengths and angles are in Table 1. There are two crystallographically independent centrosymmetric dimers in each of which two Nb(NBut)3(NHBut) units are linked by N . . . L i . . . N bridges. The four lithium cations of each dimer exhibit positional disorder and fractionally occupy six sites in the form of a cyclohexane-type ring (Fig. 1). A similar situation was observed in the related dimer [Wz(NBut)sLi4] [5]. In the present case the amido function is presumed to be contained within the bridging system, since the terminal ligand is a normal, linear 6e tert-butylimido. The two imido groups on each niobium which are involved in the bridging are bent, presumably as a result both of the lithium coordination and the over availability of g-electrons for an t8e niobium count. Whilst there may be some disorder of the three bridged ligands, linked to the disorder of the lithiums, it would seem that the amide predominantly occupies the N(n4) site, which has the longest bond and the smallest N b - - N - - C angle. The amide protons were not, however, located on a difference map. The lithium cations can formally be considered as four-coordinate. Three sites are occupied by nitrogen atoms with L i . . . N interactions ranging between 1.92(3) and 2.20(3) A, and the fourth site taken up by an "agostic" interaction with a methyl group, with L i . . . C distances ranging from 2.50(2) to 2.66(2) A. Compounds 2a and 2b show identical spectroscopic
Isodiazene complexes In a previous paper [2] we reported on the interaction of 1-amino-2,2,6,6-tetramethylpiperidine with tungsten and rhenium oxo-complexes to obtain corn-
N(11') Li(11')
~.~"Li(12)
N(14')
~
.~
(13')
s
N(12)
i
N(12')
N(13~.'~.
Nil4)
.
~
'"
~
~
Li(12') /S
Li(11)
N(ll) Fig. 1. A representation of the {[Nb(NBu~)3(NHBut)]Li2}2dimer (2a), showing all lithium sites (2/3 occupied). The Bu' carbon atoms have been omitted for clarity.
Complexes of vanadium, niobium and tantalum Table 1. Selected bond lengths (A) and angles (°) for {[Nb(NBu')3(NHBu')]Li2}2 (2a) with e.s.d.s in parentheses n=l
n=2
Nb(n)--N(nl) Nb(n)--N(n2) Nb(n)--N(n3) Nb(n)--N(n4) N(nl)--C(nl) N(n2)--C(n2) N(n3)--C(n3) N(n4)--C(n4)
1.810(6) 1.980(7) 2.000(7) 2.023(6) 1.447(10) 1.486(9) 1.500(10) 1.494(11)
1.782(6) 1.949(6) 2.011 (7) 2.029(7) 1.489(9) 1.485(9) 1.522(10) 1.478(10)
N(nl)--Nb(n)--N(n2) N(nl)--Nb(n)--N(n3) N(nl)--Nb(n)--N(n4) N(n2)--Nb(n)--N(n3) N(n2)--Nb(n)--N(n4) N(n3)--Nb(n)--N(n4) Nb(n)--N(nl)--C(nl) Nb(n)--N(n2)--C(n2) Nb(n)--N(n3)--C(n3) Nb(n)--N(n4)--C(n4) N(n2')--Li(nl)--N(n3) N(n2')--Li(nl)--N(n4) N(n3)--Li(nl)--N(n4) N(n3")--Li(nl)--N(n4) N{n4)--Li(nl )--N(n2) N(n3")--Li(nl)--N(n2) N(n3)--Li(n2)--N(n4') N(n3)--Li(n2)--N(n2)
117.9(2) 114.5(3) 116.1(3) 102.3(3) 102.3(3) 101.5(2) 175.5(5) 138.2(5) 133.4(6) 130.1(5) 116.8(11) 115.6(10) 96.7(8) --
115.9(3) 116.5(3) 115.8(3) 103.0(3) 103.0(3) 100.5(3) 177.3(6) 135.0(5) 132.2(5) 132.1(5) ---114.0(12) 92.8(9) 115.3(12) ---
N (n4')--Li (n2)--N (n2) N(n2")--Li(n2)--N(n3) N(n2")--Li(n2)--N(n4) N(n3)--Li(n2)--N(n4) N(n3')--Li(n3)--N(n2) N(n3')--Li(n3)--N(n4) N(n2)--Li(n3)--N(n4) N(n4")--Li(n3)--N(n3) N(n4")--Li(n3)--N(n2)
N (n2)--Li (n3)--N (n3)
---
112.6(10) 93.7(11) 111.0(12) ----
117.4(14) 116.7(12) 92.8(10) ---
--
117.4(12) 114.5(11) 92.1 (8) ---111.7(12) 114.4(11) 94.7(10)
Where n = 1 (molecule 1) or 2 (molecule 2) ; ' represents the symmetry transformation - x + 1, - y , - z + 1 ; " represents the symmetry transformation - x + 2, - y + 1, - z.
pounds which, on the grounds of structural data and oxidation state arguments, were classified as isodiazene complexes rather than hydrazido ( 2 ) species. Extension of this chemistry to group 5 metals led to isolation of anionic complexes (EtaNH)[M(N2C 9 H~8)2C14] (3a), M = N b ; (3b) M = T a . They were prepared in satisfactory yields in benzene from MCl5 (M = Nb, Ta) in the presence of EtaN/Me3 SiCl, which is thought to form in situ trimethylsilylhydrazine. They were crystallized from toluene as toluene solvates, which prevented informative and reproducible combustion analyses due to solvent loss. The structure of 3b was determined by X-ray crystallography and is shown in Fig. 2; selected bond lengths and angles are in Table 2. The tantalum centre
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has distorted octahedral geometry with cis-C9H~sN2 groups. Close intermolecular contacts are found between the octahedral face defined by C1(2), C1(3) and C1(4) and the triethylammonium cation [ N ( 3 ) . . . C I distances range between 3.40(1) and 3.46(1) A]. The T a - - N - - N unit is nearly linear [176.5(5) and 176.4(5)°], while the exo nitrogen atoms N(11) and N(21) are planar [angle sum 357.5(2) and 357.2(2) °, respectively]. Their planes are approximately aligned with the meridional planes of the octahedron [i.e. plane of N(11) with that defined by N(1), Ta, CI(1), C1(3) and of N(21) with that defined by N(2), Ta, CI(1) and C1(3)]. There are two types of T a - - C I distances, the longest being trans to the N ligands, indicative of a certain degree of trans influence exerted by the C9HjsN2 group. The T a - - N distances [1.865(7) and 1.882(6) A] and the N - - N distances [1.283(9) and 1.259(8) A] are both within the range between single and double bonds. Thus, metrical data of the T a - - N - - N moiety strongly support the presence of extensive n-interaction delocalized over the metal and nitrogen atoms. Various resonance forms have been invoked to describe the bonding in compounds of type MN2R4 [2], e.g. M ~- N ~ - + N R 2 M~N--NR2
M --]~+NR
2
M ~-+N--NR2
making the unambiguous assignment of formal metal oxidation states difficult. The two extreme models of hydrazido (2-) and isodiazene (0) have been encountered in the literature [2]. In the present case an isodiazene formulation is preferred, since it gives a realistic oxidation state of (Ill) for the tantalum. In support of this is the observation of Ta--CI(1) and Ya--Cl(3) distances [2.451 (2) and 2.472(2)/k], which are longer than those reported for the tantalum(V) compounds [7] [2.317(2)-2.362(2) A]. The diamagnetism of 3b may be ascribed to pairing of the two d-electrons occupying the lowest energy single orbital resulting from n-perturbation because of the isodiazene ligands. The identical 1H N M R spectra of 3a and 3b suggest that they are isostructural. Interaction of NH4VO3 with H2NNCgHI8 in neat Me3SiC1/Et3N (see Experimental) gave crystals of [(C9H,sN2)2(OSiMe3)2V(/~-O)V(O) (OSiMe3)2] (4). This could not be obtained free of siloxanes even after repeated recrystallizations from petroleum. The structure was unequivocally determined by Xray crystallography and is shown in Fig. 3 ; selected bond lengths and angles are in Table 3. It is an asymmetric oxo-bridged dimer. The coordination geometry at V(1) can be best described as trigonal bypyramidal, the axial sites are occupied by one CgH18N2 ligand and the bridging oxo atom, while an additional CgH~sN2 and two OSiMe3 groups are in the equatorial position [coordination angles: N(1)--V(1)---O(I) = 171.97(11) '~, the angles in the equatorial plane range between 117.68(12) and 120.22(11)]. The coord-
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A . A . Danopoulos et al. C(22) C(21 l) C(23) C(212)
C(112)
C(24) C(12)
o(1) C(ll) N(ll) N(1)
C(13)
C(252)
C(lll
c(251) C(14) C(151 C1(4)
c(15"~)
c1(2) c1(3)
Fig. 2. The structure of the [Ta(C9H~sN2):CI4] anion of 3b.
Table 2. Selected bond lengths (A) and (') for the [Ta(CgH~sN2)2CI4]- anion of 3b, with e.s.d.s in parentheses Ta--N(1) Ta--N(2) Ta--CI(1) Ta--CI(2) Ta--CI(3) Ta--CI(4) N(1)--N(ll) N(2)--N(21)
1.865(7) 1.882(6) 2.451 (2) 2.553(2) 2.472(2) 2.535(3) 1.283(9) 1.259(8)
CI(I)--Ta--CI(2) CI(I)--Ta--CI(3) CI( 1)--Ta--CI(4) CI(I)--Ta--N(I) CI(I)--Ta--N (2) CI(2)--Ta--CI(3) CI(2)--Ta--CI(4) CI(2)--Ta--N (1) CI(2)--Ta--N (2) CI(3)--Ta--CI(4) CI(3)--Ta--N(I) CI(3)--Ta--N (2) CI(4)--Ta--N(1) CI(4)--Ta--N(2) N(1)--Ta--N(2) Ta--N(I)--N(I 1) Ta--N (2)--N (21)
83.12(6) 163.64(7) 85.58(9) 96.3(2) 96.0(2) 84.23(6) 87.04(6) 91.2(2) 177.7(2) 83.44(9) 94.3(2) 96.2(2) 177.3(2) 90.8(2) 91.0(2) 176.5(5) 176.4(5)
short N - - N [1.285(3)-1.245(4) A], V - - N [1.725(2)1.781(3) A.] bonds and planar exo-nitrogen atoms [angle sums 356.6 and 359.9 ° around N ( l l ) and N(21), respectively], resemble those already discussed above for 3b, again pointing to an isodiazene as the best description of the nitrogen ligand. Of particular interest is the almost linear highly asymmetric oxo-bridge. In this V(2)--O(1) [1.650(2) /~] is only slightly longer than the terminal V(2)--O(6) [1.616(2) A] and is in contrast with the long W(1)--O (1) bond [2.175 (2) A,], the latter indicating weakening of the bond between V(1) and the bridging oxygen O(1). An explanation of this asymmetry could be found in the different electronic environment of the vanadium atoms: V(1), formally a V m centre, is nelectron rich and, therefore, is not involved in any n_ type interactions with the oxo-group. V(2) is more nacidic, resulting in strong vanadium-oxygen bonds. The slight difference in V--OSiMe3 distances between the two metal centres underlines the nature of siloxides as "spectator" ligands. The same compound could be obtained when using VOCI3, W205 or VOCI2(OSiMes) instead of NH4VO3 although purification was even more difficult. Replacement of the last oxo group from the vanadium proved impossible even after prolonged reaction times. EXPERIMENTAL
ination geometry at V(2) is distorted tetrahedral comprising two OSiMe3 groups, one terminal oxo and one bridging oxo atoms. The metrical data for the V - - N - - N moiety on V(1) observed here, e.g.
Analyses were by the Imperial College microanalytical laboratory. All operations were carried out under purified Ar or N2, or in a Vacuum Atmospheres
Complexes ofvanadium, niobium and tantalum
1085
C(152)
C(13)
C(28)
C(14)
C(112) C(12) C(26) C(151) N(11
~i(2) C(16) C(17)
C(lll) 0(2)
Si(l)
c(252)
C(251)
C(31) ~_ 0,(1) )C(18) s(21) ~
C(212){ C(211)
c(2D
O
(
6
)
0(4) ~ ] Si(3ff'~'==='=~
C(32)
c(24)
c(23)
C(22)
J%(5.,
(~
,)
C(41)
C(~)
C(42) Fig. 3. The structure of [(CgHlaN2)2(OSiMe3)2V(#-O)V(O)(OSiMe3)2] (4).
glove-box. All solvents were degassed and distilled before use. N M R data were obtained using a JEOL EX-270 or Bruker Avance DRX-300 spectrometer operating at 270 or 300 MHz (~H), respectively, and referenced to the residual proton impurity in the solvent (3 7.15 C6D6). Mass spectra were obtained on a VG-7070E or VG Autospec spectrometers. Commercial chemicals were from Aldrich and Avocado Chemicals. The following starting materials were prepared according to literature procedures: [Nb(NBu') (HNBut) (H2NBut)C12]2 [8], [Ta(NBut)(NHBu t) (H2NBut)C12]2 [8] H2NNCgHIs [9]. ButNHLi was obtained by interaction of BunLi with ButNH2 in hexanes. The petroleum used throughout had a boiling point of 40-60°C.
Dilithiumtris(tert-butylimido)(tert-butylamido) niobate(2a) To a solution of [(Bu t N)Nb(HNBu t )(H2NBu t )C1212 (0.76 g, 1 mmol) at - 7 8 ° C in Et20 (ca 50 cm 3) was added a suspension of ButNHLi [0.79 g, 10 mmol in
EhO (30 cm3)]. The mixture was allowed to warm to room temperature and stirred overnight. Evaporation of volatiles under reduced pressure, extraction of residue with hot petroleum (5 x 30 cm3), filtration and concentration of filtrate to ca 30 cm 3 and standing at room temperature overnight gave colourless prisms. Yield 0.55 g 70%; m.p. > 230°C (decomposition). X-ray quality crystals were obtained by slow cooling solutions in toluene. [Found (calc.) : C, 49.2 (49.1); H, 9.4 (9.4) ; N, 15.0 (14.3)%]. N M R (C6D6) : ~H: 6 2.6 (s, br, IH, NHCMe3), 1.83, 1.62, 1.59 (s, 9H each, NCMe3), 1.47 (s, 9H, NHCMe3). 7Li: 5 2.5 and 2.0.
Dilithiumtris(tert-butylimido)(tert-butylamido) tantalat e(2b) As for 2a, but from [(Bu'N)Ta(HNBu ~) (H2NBut)C12]2 (0.94 g, 1 mmol) and ButNHLi (0.79 g, 10 mmol). Yield 0.69 g, 75% ; m.p. > 230°C (decomposition). [Found (calc.) : C, 39.8 (40.0); H, 7.5 (7.7); N, 11.6 (11.7)%]. N M R (C6D6) ~H: ~ 2.6 (s, br, 1H, NHCMe3), 1.73, 1.49, 1.47 (s, 9H each, NCMe3), 1.37 (s, 9H, NHCMe3). 7Li: 6 2.5 and 2.0.
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A. A. Danopoulos et al.
Table 3. Selected bond lengths (A) and angles (°) for [(CgHIsN2)2(OSiMe3)2V(/~-O)V(O)(OSiMe3)]2 (4) with e.s.d.s in parentheses V(1)--N(1) V(I)--N(2) V(1)--O(I) V(1)--O(2) V(1)--O(3) V(2)--O(1) V(2)--O(4) V(2)~O(5) V(2)--O(6) Si(1)--O(2) Si(2)--O(3) Si(3)--O(4) Si(4)--O(5) N(I)--N(11) N(2)--N(21)
1.725(2) 1,781(3) 2.175(2) 1.827(2) 1.813(2) 1,650(2) 1.806(2) 1.810(2) 1,616(2) 1,626(2) 1.619(2) 1.633(2) 1.645(2) 1.285(3) 1.245(4)
N(I)--V(1)--N(2) N(1)--V(1)--O(1) N(1)--V(1)---O(2) N(1)--V(1)--O(3) N(2)--V(I)--O(1) N(2)--V(I)--O(2) N(2)--V(1)--0(3) O(1)--V(1)--O(2) O(1)--V(1)--O(3) O(2)--V(1)--O(3) V(I)--N(1)--N(I 1) V(I)--N(2)--N(21) V(I)--O(I)--V(2) V(1)--O(2)--Si(1) V(1)--O(3)--Si(2) O (1)--V(2)--O(4) O(1)--V(2)--O(5) O ( 1)--V (2)--O (6) O(4)--V(2)--O(5) O(4)--V(2)--O(6) O(5)--V(2)--O(6) V(2)--O(4)--Si(3) V(2)--O(5)--Si(4)
91.86(12) 171.97(! 1) 96.72(11) 98.91(12) 80.32(10) 117.68(12) 119.00(12) 85.42(9) 86.59(9) 120.22(11) 176.4(2) 174.3(2) 162.93(13) 142.11(14) 162.89(14) 111.07(11) 110.42(11) 109.64(12) 108.46(11) 110.34(11) 106.81(11) 148.00(14) 128.22(13)
( T r i e t h y l a m m o n i u m ) [tetrachlorobis(2,2,6,6-tetrarnethylpiperid-l-ylnitrene)tantalate(lll) (3b) and niobate(Ill) (3a)
To TaC15 (0.3 g, 0.84 mmol) in benzene (10 cm 3) was added sequentially Et3N (0.58 g, 4.2 mmol), 1amino-2,2,6,6-tetramethylpiperidine (0.32 g, 2.1 mmol) then Me3SiCI (0.53 g, 4.2 mmol). The mixture was stirred and refluxed under N2 overnight. After cooling and removal of all volatiles in vacuo, the residue was washed with petroleum (20 cm 3) and extracted with toluene (2 x 30 cm3). After filtration, reduction of volume of toluene to ca 15 cm 3 and cooling to -20°C, orange-red crystals were obtained. Yield 0.36-0.48 g, 60-70%. Recrystallization from toluene yielded crystals of X-ray quality. The crystals
decomposed on drying in vacuo due to facile removal of toluene. Consequently, no satisfactory analytical results were obtained. ~H N M R of various samples showed the presence of toluene to varying concentrations. N M R (C6D6) ~H: 6 9.42 (s, br, 1H, Et3NH), 2.56 [pseudoquartet, br, 6H (CH3CH2)3NH ], 1.85 (s, 12H, Me4CsH6), 1.77 (s, 12H, Me4CsH6), 1.33 (m, 12H, Me4CsH6), 0.78 (t, br, 9H, (CH3CHz)3NH]. The corresponding niobium compound could be prepared in the same way with or without the presence of C6H6. However, toluene was lost more readily from the final crystalline material. N M R (C6D6) ~H : 6 9.42 (s, br, IH, Et3NH), 2.56 [pseudoquartet, br, 6H (CH3CH2)3NH], 1.85 (s, 12H, Me4CsH6), 1.77 (s, 12H, Me4CsH6), 1.33 (m, 12H, Me4CsH6), 0.78 [t, br, 9H, (CH3CH2)3NH]. [Bis(2,2,6,6-tetramethylpiperid- 1-ylnitrene)bis(trimethyl siloxo)]vanadium(la-oxo)[bis(trimethylsiloxo)oxo] vanadium (4)
This compound could be prepared using any of the following starting materials, VOCI3, NH4VO3, V205, VOCI2(OSiMe3) [prepared from VOC13 using (Me3Si)20 in the presence of Et3N and Me3SiC1] without benzene as solvent. NH4VO3 gave the cleanest product. To NH4VO3 (0.6 g, 6 mmol) was added sequentially with stirring, EtaN (8 g, 25 mmol), 1amino-2,2,6,6-tetramethylpiperidine (2.3 g, 15 mmol) then Me3SiCI (8 cm 3, 25 mmol) and the mixture refluxed overnight. After cooling the volatiles were removed under vacuum and the dark residue was extracted with petroleum (2 x 50 cm3). After concentration of extracts in vacuo to ca 5 cm 3 and cooling to -30°C, dark violet crystals were obtained. X-ray quality crystals were obtained after recrystallization from petroleum. Yield: 0.25 g, 20-30%. Repeated recrystallization from petroleum did not yield crystals of analytical purity due to contamination by siliconcontaining oils and starting piperidine, as proved by NMR. N M R (C6D6) IH: 6 1.47 (s, 12H, Me4CsH6), 1.01, 0.89, 0.86, 0.82 (each s, 6H, Me4CsH6), 0.35 (s, 18H, OSiMe3), 0.28 (s, 18H, OSiMe3). X-ray crystalloyraphy
X-ray data for compounds 2a, 3b and 4 were collected at low temperature (see Table 4) using a FAST TV area detector diffractometer with Mo-K~ radiation (2 = 0.71069 A), as previously described [10]. The structures were solved via direct methods procedures of SHELXS-86 [11], and refined by full-matrix leastsquares on F~0, using the program SHELXL-93 [12]. All unique data used were corrected for Lorentz polarization factors and for absorption using the program DIFABS [13], with maximum and minimum correction factors listed in Table 4. The non-hydrogen atoms were refined with anisotropic thermal parameters and the hydrogen atoms of 2a and 3b were
Complexes of vanadium, niobium and tantalum
1087
Table 4. Crystal data and structure refinement details for compounds 2a, 3b and 4 Compound Formula
2a
3b
C32H74LiaNsNb2
CIsH36CI4N4Ta •
Mr Crystal system Space group a (A) b (A) c (A.) ~(~') fl('') 7(') U (/~3) Z Dc (Mg m -3) F(000) Crystal size (mm) p(Mo-K,) (mm-z) Reflections collected Independent reflections (R~,,) Data, restraints, parameters Goodness of fit, F 2 Final R indices R~, wR:, [I> 2a(/)] R,, wR2 (all data) Largest differencepeak and hole (e A -3)
784.56 Triclinic PI 10.22(2) 13.92(2) 15.916(7) 92.26(13) 100.7(2) 90.81 (4) 2222(4) 2 1.173 824 0.18 × 0.18 × 0.15 0.499 9384 6117 (0.0718) 6112, 0, 465 1.035 0.0540, 0.1080 0.0923, 0.1196 0.753, -0.499
4 C5oH72N406Si4V2
C7H8"C6H,6N 825.59 Monoclinic P2~/c 10.198(8) 25.180(10) 15.292(10) 90 106.46(7) 90 3766(2) 4 1.456 1688 0.42 × 0.15 × 0.12 3.229 14662 5596 (0.0642) 5589, 0, 366 1.067 0.0504, 0.1215 0.0665, 0.1472 3.632, -0.885
799.16 Triclinic Pi 10.087(3) 12.597(4) 18.823(2) 70.65(I) 87.77(5) 87.20(2) 2253(I) 2 1.178 860 0.36 × 0.18 × 0.12 0.546 9619 6225 (0.0537) 6215, 0, 483 0.965 0.0421, 0.1016 0.0574, 0.1400 0.581, -0.342
S = [Z(w(Fo2-F:c):f(n-p))]'/:; R, = XI(Fo-F¢)]/XFo; wR2 = [Xw(H - H)~/Xw(Fo:):]'/: ; w = l/[,r:(H)+ (xP) 2+gP]; P = [max(F2) + 2(F~)]/3. Where n = number of reflections,p = total number of parameters, x = 0, 0.0716, 0.0527 and g = 0, 0, 0 for compounds 2a, 3b and 4, respectively.
included in idealised positions. Due to the uncertainties in positioning, hydrogen atoms on the Bu t methyl groups of I associated with the Li interactions were omitted. The methylene protons of 4 were experimentally located whilst the methyl hydrogen atoms were placed in calculated positions. The solvent of crystallization, toluene, within the lattice of 3b was shown to exhibit positional disorder. The carbon atoms were refined in split sites with partial occupancy factors and consequently hydrogen atoms were ignored in the refinement. All crystal data and refinement details are summarized in Table 4. Additional material available from the Cambridge Crystallographic Data Centre comprises fractional atomic co-ordinates, thermal parameters and remaining bond lengths and angles.
2.
3. 4. 5.
6.
7.
Acknowledyements--We thank the EPSRC for support (A.A.D. and R.S.H.-M.) and for provision of X-ray facilities. REFERENCES
8. 9.
1. Danopoulos, A. A., Wilkinson, G., HussainBates, B. and Hursthouse, M. B., (a) J. Chem. Soc., Dalton Trans. 1990, 2753 ; (b) Danopoulos, A. A. and Wilkinson, G., Polyhedron, 1990, 9,
10.
1009; (c) Danopoulos, A. A., Longley, C. J., Wilkinson, G., Hussain, B. and Hursthouse, M. B., Polyhedron, 1989, 8, 1767; (d) Danopoulos, A. A., Wilkinson, G., Sweet, T. K. N. and Hursthouse, M. B., J. Chem. Soc., Dalton Trans. 1994, 1037. Danopoulos, A. A., Wilkinson, G. and Williams, D. J., J. Chem. Soc., Dalton Trans. 1994, 907, and refs therein. Wigley, D. E., Pro9. Inory. Chem. 1994, 42, 239. Smith, D. P., Allen, K. D., Carducci, M. D. and Wigley, D. E., Inory. Chem. 1992, 31, 1319. Danopoulos, A. A., Wilkinson, G., Hussain, B. and Hursthouse, M. B., J. Chem. Soc., Chem. Commun. 1989, 896. Hankin, D. M., Danopoulos, A. A., Wilkinson, G., Sweet, T. K. N. and Hursthouse, M. B., J. Chem. Soc., Dalton Trans. 1996, 1309. (a) Cotton, F. A., Durag, S. A. and Roth, W. J., Acta Cryst. 1985, C41, 881; (b) Lavasseur, G. and Beauchamp, A. L., Acta Cryst. 1991, C47, 547, and refs therein. Bates, P. A., Nielson, A. J. and Waters, J. M., Polyhedron, 1985, 4, 1391. Hinsberg III, W. D., Schultz, P. G. and Dervan, P. B., J. Am. Chem. Soc. 1982, 104, 766. Danopoulos, A. A., Wilkinson, G., HussainBates, B. and Hursthouse, M. B., J. Chem. Soc., Dalton Trans. 1991, 1855.
1088
A . A . Danopoulos et al.
11. Sheldrick, G. M., SHELXS-86, Acta Cryst. 1990, A46,467. 12. Sheldrick, G. M., SHELXL-93, Program for Crystal Structure Refinement. University of G6ttingen, Germany, 1993.
13. Walker, N. P. C. and Stuart, D., Acta Cryst. 1983, A39, 158 adapted for FAST geometry by A. Karaulov, University of Wales, Cardiff, 1991.