Oxidation reactions of [(Me3Si)2N]2VX(THF) (X = Cl, Me, Ph) with CuCl, PhCH(O)CH2, and Ph2CN2 and the syntheses and structures of the vanadium(III) anions {[(Me3Si)2N]

Article abstract of DOI:10.1021/om970458i

One-electron oxidation of [(Me₃Si)₂N]₂VX(THF) (X = Cl, Me, Ph) with CuCl afforded the V(FV), d¹ species [(Me₃Si)₂N]₂VCl(X) in moderate yields after crystallization from acetonitr

Full text of DOI:10.1021/om970458i

5148
Organometallics 1997, 16, 5148-5157
Oxid a tion Rea ction s of [(Me3Si)2N]2VX(THF ) (X ) Cl, Me,
P h ) w ith Cu Cl, P h CH(O)CH2, a n d P h 2CN2 a n d th e
Syn th eses a n d Str u ctu r es of th e Va n a d iu m (III) An ion s
{[(Me3Si)2N]2VX2}- (X ) Cl, Me)
Christopher P. Gerlach and J ohn Arnold*
Department of Chemistry, University of California, Berkeley, California 94720-1460
Received J une 2, 1997X
One-electron oxidation of [(Me3Si)2N]2VX(THF) (X ) Cl, Me, Ph) with CuCl afforded the
V(IV), d1 species [(Me3Si)2N]2VCl(X) in moderate yields after crystallization from acetonitrile.
[(Me3Si)2N]2VCl2 has been characterized crystallographically. The methyl and phenyl
derivatives were conveniently synthesized in one step from [(Me3Si)2N]2VCl(THF) by first
reacting first with LiMe or MgPh2, prior to treatment with CuCl. Reaction of [(Me3Si)2-
N]2VCl(THF) with dilithioacetylide in the presence of tetramethylethylenediamine (TMEDA)
proceeded with redistribution of the Cl ligands, as the anionic V(III) compound [Li(TMEDA)2]-
{[(Me3Si)2N]2VCl2} was obtained in 44% yield as purple crystals. The analogous dimethyl
anion [Li(TMEDA)2]{[(Me3Si)2N]2VMe2} was synthesized in 66% yield as deep-blue, highly
air-sensitive crystals on treatment of [(Me3Si)2N]2VCl(THF) with 2 equiv of LiMe in the
presence of TMEDA. X-ray crystallography showed that both salts crystallized as well-
separated cations and anions. The reaction between styrene oxide and [(Me3Si)2N]2-
VMe(THF) proceeded stepwise, first yielding the µ-O intermediate {[(Me3Si)2N]2VMe}2(µ-
O) and then the V(V) terminal oxo [(Me3Si)2N]2V(O)(Me). Styrene oxide also oxidized
[(Me3Si)2N]2VPh(THF) to [(Me3Si)2N]2V(O)(Ph), however, in this case the putative µ-O
intermediate could not be isolated as a stable material. Diphenyldiazomethane was reduced
by two electrons to an alkylidenehydrazido(2-) on displacing THF from [(Me3Si)2N]2VCl(THF)
to form the V(V) complex [(Me3Si)2N]2V(Cl)(N2CPh2). A crystal structure showed the
diazoalkane to be coordinated in a doubly-bent fashion.
In tr od u ction
CH2SiMe3),8-11 we recently showed that the {[(Me3Si)2-
N]2V}+ fragment12 can stabilize three-coordinate V(III)
selenolate and tellurolate complexes12 and [(Me3Si)2N]2-
VMe(THF),13 a rare “Cp-free” vanadium-hydrocarbyl.
In this paper, we report the one-electron oxidation of
this latter V-Me complex, the analogous V-Ph com-
plex, and the parent V(III) chloride complex to yield the
bis(amide) V(IV) methyl-chloride, phenyl-chloride, and
dichloride derivatives, respectively. This last species
completes the homologous series of group 5 [(Me3Si)2N]2-
MCl2 compounds (M ) V, Nb, Ta), as the niobium14,15
and tantalum16,17 analogs were recently reported by
Hoffman. The syntheses and structures of related four-
coordinate V(III) anions, i.e., {[(Me3Si)2N]2VCl2}- and
{[(Me3Si)2N]2VMe2}-, are also reported. We have also
explored the two-electron oxidation chemistry of these
species, which yields V(V) terminal oxo species [(Me3Si)2-
N]2NV(O)(R). In the case of the methyl derivative, the
The ability of amido ligands to support and promote
unusual chemistry at metal centers has been known for
many years.1 In this context, they complement the well-
studied Cp-based systems, with the major difference
being the greater reactivity of the former complexes due
to their relatively higher unsaturation and lower coor-
dination numbers for a given LnM (L ) NR2 or Cp).
Recent work probing the electronic effects of the sub-
stituents on the amide nitrogen has lead to a number
of interesting results, such as fixation2 and scission3-5
of dinitrogen. Our focus here is on the more traditional
bis(trimethylsilyl)amide ligand, developed extensively
throughout the years by workers such as Bradley,
Lappert, and Andersen, which is the prototypical bulky
amide for stabilizing low-coordinate, electrophilic metal
fragments.6 Although it was recognized early on7 that
in some systems the use of -N(SiMe3)2 as an ancillary
ligand could lead to intramolecular γ-hydrogen elimi-
naton across M-X bonds (X ) Cl, H/D, Me, Et,
(8) Simpson, S. J .; Turner, H. W.; Andersen, R. A. J . Am. Chem.
Soc. 1979, 101, 7728.
X Abstract published in Advance ACS Abstracts, November 1, 1997.
(1) Lappert, M. F.; Power, P. P.; Sanger, A. R.; Srivastava, R. C.
Metal and Metalloid Amides; Ellis Horwood: Chichester, U.K., 1980.
(2) Gambarotta, S. J . Organomet. Chem. 1995, 500, 117.
(3) Laplaza, C. E.; Cummins, C. C. Science 1995, 268, 861.
(4) Laplaza, C. E.; J ohnson, A. R.; Cummins, C. C. J . Am. Chem.
Soc. 1996, 118, 709.
(5) Laplaza, C. E.; J ohnson, M. J . A.; Peters, J . C.; Odom, A. L.;
Kim, E.; Cummins, C. C.; George, G. N.; Pickering, I. J . J . Am. Chem.
Soc. 1996, 118, 8623.
(9) Simpson, S. J .; Andersen, R. A. Inorg. Chem. 1981, 20, 3627.
(10) Simpson, S. J .; Turner, H. W.; Andersen, R. A. Inorg. Chem.
1981, 20, 2991.
(11) Planalp, R. P.; Andersen, R. A.; Zalkin, A. Organometallics
1983, 2, 16.
(12) Gerlach, C. P.; Arnold, J . Inorg. Chem. 1996, 35, 5770.
(13) Gerlach, C. P.; Arnold, J . Organometallics 1996, 15, 5260.
(14) Bott, S. G.; Hoffman, D. N.; Rangarajan, S. P. Inorg. Chem.
1995, 4305.
(15) Hoffman, D. M.; Rangarajan, S. P. Polyhedron 1993, 12, 2899.
(16) Hoffman, D. M.; Suh, S. J . Chem. Soc., Chem. Commun. 1993,
714.
(6) Cummins, C. C. Chem. Rev., in press.
(7) Bennett, C. R.; Bradley, D. C. J . Chem. Soc., Chem. Commun.
1974, 29.
(17) Suh, S.; Hoffman, D. M. Inorg. Chem. 1996, 35, 5015.
S0276-7333(97)00458-5 CCC: $14.00 © 1997 American Chemical Society

Oxidation Reactions of [(Me3Si)2N]2VX(THF)
Organometallics, Vol. 16, No. 24, 1997 5149
with hexanes (50 mL) and filtered. The filtrate was evapo-
rated under reduced pressure to a red residue, which was
extracted with MeCN (40 mL). The filtrate was concentrated
to ca. 30 mL and cooled to -25 °C for 14 h. Red crystals of
the product (735 mg, 78%) were isolated by filtration and dried
under vacuum.
reaction proceeds stepwise through an isolable µ-O
intermediate {[(Me3Si)2N]2VMe}2(µ-O). The synthesis
and structure of [(Me3Si)2N]2VCl(N2CPh2), formed in
what may also be viewed as an oxidation reaction, is
also presented. Lastly, given the well-established ease
of interconversion between Cp2V, Cp2VX, and Cp2VX2
species,18 illustrative comparisons will be made between
the chemistry of {Cp2V} versus {[(Me3Si)2N]2V} sys-
tems.
Meth od B. [(Me3Si)2N]2VCl(THF) (3.98 g, 8.30 mmol) was
dissolved in THF (40 mL) and treated with LiMe (5.6 mL, 1.48
M in Et2O). After the mixture was stirred for 1 h, it was added
to CuCl (822 mg, 8.30 mmol), giving a deep red mixture along
with metallic Cu. After the mixture was stirred for 6 h, the
volatile materials were removed under reduced pressure.
Extraction with MeCN (2 × 75 mL) and then Et2O (30 mL)
was followed by filtration and concentration of the combined
filtrates. Cooling to -25 °C for 24 h yielded 2.15 g (61%) of
brick-red product, which was isolated by filtration and dried
under vacuum. Mp: 51-55 °C (dec). 1H NMR (0.11 M): δ
1.1 (∆ν1/2 ca. 150 Hz). IR: 1404 (w), 1299 (w), 1261 (m sh),
1252 (s), 877 (vs), 856 (vs), 845 (vs), 791 (s), 765 (m), 715 (s),
676 (m), 656 (w), 646 (m), 618 (w), 575 (w), 542 (w), 508 (m),
440 (m) cm-1. µeff ) 1.69 µB (C6D6). EIMS: 421 (M+, correct
isotope pattern). Anal. Calcd for C13H39ClN2Si4V: C, 36.98;
H, 9.31; N, 6.64. Found: C, 36.85; H, 9.27; N, 6.63.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. Standard inert atmosphere
glovebox and Schlenk-line techniques were employed for all
manipulations. All solvents were predried over 4 Å molecular
sieves, and in the case of benzene, hexanes, diethyl ether, and
tetrahydrofuran (THF), the solvents were distilled from purple
sodium/benzophenone ketyl under N2. Tetramethylethylene-
diamine (TMEDA) and hexamethyldisiloxane (HMDSO) were
distilled from sodium, while acetonitrile was distilled from
CaH2. [(Me3Si)2N]2VX(THF) (X ) Cl,19 Me13), MgPh2,20
22
Ph2CN2,21 and (THF)xLi2C2 were prepared according to
literature procedures. A diethyl ether solution of LiMe was
purchased from Aldrich. Styrene oxide was distilled and
degassed prior to use. CuCl was dried overnight under
vacuum at 160 °C. Samples for IR spectroscopy were prepared
as mineral oil mulls between KBr plates. Conductivity
measurements were made in acetonitrile at ambient temper-
ature. 1H and 13C{1H} NMR spectra were recorded on a 300
MHz spectrometer at ambient temperature, using C6D6 as the
solvent unless otherwise noted. 51V NMR spectra were
measured at 78.94 MHz and externally referenced to neat
VOCl3 at 0 ppm. Melting points were determined under N2
in flame-sealed capillary tubes. Magnetic susceptibility mea-
surements were made by the method of Evans23,24 and are
uncorrected. C, H, N and EIMS analyses were performed at
the analytical facilities within the College of Chemistry,
University of California, Berkeley. X-ray data were collected
and the structures solved at the University of California at
Berkeley chemistry X-ray facility (CHEXRAY, Dr. F. J . Hol-
lander, supervisor).
[(Me3Si)2N]2VCl2. [(Me3Si)2N]2VCl(THF) (7.84 g, 16.4 mmol)
and CuCl (1.62 g, 16.4 mmol) were mixed with THF (100 mL),
giving a deep red solution and a precipitate of metallic Cu.
After the mixture was stirred for 1 h, the volatile materials
were removed under reduced pressure. The solid was ex-
tracted with hexanes (125 mL and 30 mL), and the filtrate
was stripped dry under reduced pressure. The solid was then
extracted with MeCN (125 mL and 50 mL), filtered, and then
concentrated to ca. 100 mL and cooled to -25 °C. Red crystals
(4.36 g, 60%) of the product were isolated in two crops by
filtration. Mp: 95-105 °C (dec). 1H NMR (0.10 M): δ 0.6
(∆ν1/2 ca. 135 Hz). IR: 1406 (m), 1266 (s sh), 1263 (s), 1155
(w), 1096 (w), 847 (s), 790 (s), 711 (s), 677 (s), 642 (s) cm-1. µeff
) 1.68 µB (C6D6). Anal. Calcd for C12H36Cl2N2Si4V: C, 32.56;
H, 8.20; N, 6.33. Found: C, 32.63; H, 8.33; N, 6.16.
[(Me3Si)2N]2V(Cl)(P h ). [(Me3Si)2N]2VCl(THF) (1.03 g, 2.15
mmol) and MgPh2 (192 mg, 1.08 mmol) were mixed with THF
(30 mL), giving a deep blue solution. After 1.5 h, the mixture
was added to CuCl (213 mg, 2.15 mmol), giving a dark orange-
red mixture. After the mixture was stirred overnight, the
volatile materials were removed under reduced pressure. The
residue was extracted with hexanes (50 mL), and the filtrate
was stripped dry under reduced pressure, leaving an oily
residue that was redissolved in 20 mL of MeCN. Concentra-
tion, followed by cooling to -25 °C, afforded 440 mg (42%) of
brick-red crystals, which were isolated by filtration and dried
under vacuum. Mp: 82-86 °C (dec). 1H NMR (0.08 M): δ
1.1 (∆ν1/2 ca. 325 Hz). IR: 1301 (w), 1265 (m sh), 1252 (s),
1053 (w), 993 (w), 879 (s), 850 (vs), 790 (s), 767 (m), 710 (s),
693 (m), 676 (m), 658 (w), 646 (m), 589 (w), 453 (w), 439 (m),
426 (m), 405 (m) cm-1. µeff ) 1.69 µB (C6D6). Anal. Calcd for
C
18H41ClN2Si4V: C, 44.64; H, 8.53; N, 5.78. Found: C, 44.27;
H. 8.64; N, 5.81.
[Li(TMEDA)2]{[(Me3Si)2N]2VCl2}. [(Me3Si)2N]2VCl(THF)
(1.53 g, 3.20 mmol) and Li2C2‚0.17(THF) (165 mg, 3.29 mmol)
were mixed with Et2O (30 mL). The blue-green mixture
gradually darkened to black, and after 15 min TMEDA (1.5
mL, 9.9 mmol) was added. After 24 h, the volatile materials
were removed under reduced pressure. The black solid was
extracted with Et2O (25 mL), and the solution was filtered from
some pyrophoric black solid. Concentration of the filtrate to
ca. 10 mL followed by slow-cooling to -25 °C for 24 h afforded
965 mg (44% on V) of purple needles, which were isolated by
filtration and dried under vacuum. Hydrocarbon solutions of
the salt have a blue appearance. Large, purple, tabular
crystals may be grown by slowly recrystallizing the material
from diethyl ether. Mp: 97-99 °C (dec). 1H NMR (CD3CN,
300 MHz): δ 2.8 (SiMe3, ∆ν1/2 ca. 200 Hz), 2.32 (s, 8H, TMEDA-
CH2), 2.17 (s, 24H, TMEDA-CH3). IR: 1359 (m), 1292 (m),
1242 (s), 1186 (w), 1163 (m), 1132 (m), 1101 (w), 1070 (w), 1036
(m), 1017 (m), 948 (s), 924 (vs), 886 (s), 852 (s), 837 (s), 783
[(Me3Si)2N]2V(Cl)(Me). Meth od A. [(Me3Si)2N]2VMe(THF)
(1.02 g, 2.23 mmol) and CuCl (222 mg, 2.24 mmol) were mixed
with THF (30 mL). The mixture turned green, and over about
10 s it became red with metallic Cu apparent. After the
mixture was stirred for 10 min, the volatile materials were
removed under reduced pressure. The red solid was extracted
(s), 762 (m), 722 (w), 692 (m), 669 (m), 635 (m), 615 (w) cm-1
.
µeff ) 2.64 µB (C6D6). ΛM (MeCN, 1.29 × 10-3 M): 92 S cm2
mol-1. Anal. Calcd for C24H68Cl2LiN6Si4V: C, 42.27; H, 10.05;
N, 12.32. Found: C, 42.36; H, 10.05; N, 12.29.
[Li(TMEDA)2]{[(Me3Si)2N]2VMe2}. A Et2O solution of
LiMe (4.0 mL, 5.9 mmol) was added to 20 mL of Et2O. TMEDA
(0.90 mL, 6.0 mmol) was then added, followed by a Et2O
solution (20 mL) of [(Me3Si)2N]2VCl(THF) (1.42 g, 2.96 mmol).
The mixture turned deep blue and was stirred for 2 h before
the volatile materials were removed under reduced pressure
leaving a blue solid. Extraction with Et2O (25 mL), followed
by concentration and cooling of the filtrate to -25 °C for 24 h,
afforded 1.26 g (66% on V) of blue crystals. Mp: 146-148 °C
(dec). 1H NMR (CD3CN, 300 MHz): δ 2.34 (s, 4H, TMEDA-
(18) Berno, P.; Gambarotta, S.; Richeson, D. In Comprehensive
Organometallic Chemistry II; Abel, E. D. Stone, F. G. A., Wilkinson,
G., Eds.; Elsevier Science: New York, 1995; Vol. 5, p 1.
(19) Berno, P.; Moore, M.; Minhas, R.; Gambarotta, S. Can. J . Chem.
1996, 74, 1930.
(20) Andersen, R. A.; Wilkinson, G. J . Chem. Soc., Dalton Trans.
1977, 809.
(21) Miller, J . B. J . Org. Chem. 1959, 24, 560.
(22) Walton, D. R. M.; Waugh, F. J . Organomet. Chem. 1972, 37,
45.
(23) Evans, D. F. J . Chem. Soc. 1959, 2003.
(24) Schubert, E. M. J . Chem. Educ. 1992, 69, 62.

5150 Organometallics, Vol. 16, No. 24, 1997
Gerlach and Arnold
CH2), 2.19 (s, 12H, TMEDA-CH3); a broad, low intensity signal
whose maximum lay just downfield of the TMEDA-CH2 signal
tailed out to ca. 3 ppm. IR: 1357 (m), 1291 (s), 1236 (s), 1185
(m), 1162 (m), 1130 (m), 1099 (m), 1066 (m), 1037 (s), 1019
(s), 975 (vs), 887 (s), 864 (vs), 842 (vs), 788 (s), 778 (s), 755
(m), 722 (w), 698 (m), 666 (s), 625 (s), 612 (m), 588 (w), 533
(w), 485 (m) cm-1. µeff ) 2.57 µB (CD3CN). ΛM (MeCN, 1.24 ×
°C): δ 7.71 (“d”, 4H, o-Ph), 7.21-7.13 (m, 6H, m- and p-Ph),
0.45 (s, 36H, -SiMe3). 13C{1H} NMR (100 MHz, 23 °C): δ
157.5 (N2CPh2), 135.5, 134.8 (i-Ph), 131.1 (o- or m-Ph), 130.9
(p-Ph), 130.5 (p-Ph′), 129.9 (o- or m-Ph′), 128.7 (coincident o-
or m-Ph and Ph′), 5.7 (-SiMe3). 13C{1H} NMR (100 MHz, 97
°C): δ 135.6 (i-Ph), 130.6 (o- or m-Ph), 130.4 (p-Ph), 128.7 (o-
or m-Ph). 51V NMR (78.94 MHz): δ 285 (∆ν1/2 ca. 485 Hz).
IR: 1331 (m), 1262 (m), 1249 (s), 1218 (w), 1075 (m), 1040 (m),
952 (w), 881 (s), 845 (s), 787 (s), 722 (m), 699 (m), 689 (m),
10-3 M): 92 S cm2 mol-1
. Anal. Calcd for C26H74LiN6Si4V:
C, 48.71; H, 11.63; N, 13.11. Found: C, 48.44; H, 11.46; N,
13.98.
672 (m), 644 (w), 559 (w) cm-1
. Anal. Calcd for C25H46Cl-
N4Si4V: C, 49.93; H, 7.71; N, 9.32. Found: C, 50.18; H, 7.91;
N, 9.26.
X-r a y Cr ysta llogr a p h y. A summary of crystal data, data
collection, and refinement for all crystallographically charac-
terized compounds is given in Table 1. A list of selected bond
lengths and bond angles is given in Table 2.
[(Me3Si)2N]2VCl2. Red crystals were grown from aceto-
nitrile at -25 °C. A suitable crystal was mounted on a glass
capillary under Paratone-N hydrocarbon oil. The crystal was
transferred to a Siemens SMART diffractometer/CCD area
detector25 and cooled by a nitrogen-flow low-temperature
apparatus which had been previously calibrated by a thermo-
{[(Me3Si)2N]2VMe}2( -O). A hexanes solution (40 mL) of
[(Me3Si)2N]2VMe(THF) (804 mg, 1.75 mmol) was treated with
PhCH(O)CH2 (0.10 mL, 0.88 mmol), giving a forest-green
mixture that was stirred for 16 h. The volatiles were removed
under reduced pressure, and the solid was extracted with
HMDSO (2 × 30 mL). The extracts were filtered and concen-
trated to ca. 15 mL. Cooling to -25 °C for 24 h afforded 450
mg (65%) of dark crystals, which were dried under vacuum.
The crystals dissolved giving forest-green solutions. Mp: 111-
113 °C (dec). 1H NMR (0.08 M): δ 1.85 (∆ν1/2 ca. 90 Hz). IR:
1264 (m sh), 1251 (s), 882 (s), 858 (s), 786 (m), 750 (m), 709
(s), 672 (m), 657 (s), 643 (m), 557 (m), 503 (m) cm-1
. µeff )
2.46 µB (1.74 µB per V, C6D6). Anal. Calcd for C26H78N4-
OSi8V2: C, 39.55; H, 9.96; N, 7.10. Found: C, 39.32; H, 9.91;
N, 6.85.
couple placed at the same temperature as the crystal. A
preliminary orientation matrix and unit cell parameters were
determined by collecting 60, 10 s frames, followed by spot
integration and least-squares refinement. A hemisphere of
data was collected using 0.3° ω scans at 10 s per frame. The
raw data were integrated (XY spot spread ) 1.60°; Z spot
spread ) 0.60°), and the unit cell parameters were refined
(7930 reflections with I > 10σ(I)) using SAINT.26 The acentric,
orthorhombic space group P212121 (No. 19) was uniquely
defined by the systematic absences. Preliminary data analysis
Gen er a tion of [(Me3Si)2N]2V(O)(Me). Meth od A.
A
C6D6 solution (ca. 0.5 mL) of [(Me3Si)2N]2VMe(THF) (8.6 mg,
0.019 mmol) in a Teflon sealable NMR tube was treated with
PhCH(O)CH2 (2.1 µL, 0.018 mmol), giving a green solution.
Analysis by 1H NMR spectroscopy showed a mixture of styrene
oxide, styrene, [(Me3Si)2N]2V(O)(Me), and {[(Me3Si)2N]2VMe}2(µ-
O). After 24 h, the solution was a clear yellow and analysis
by 1H NMR indicated the presence of only styrene and
[(Me3Si)2N]2V(O)(Me) in solution.
and a semiempirical ellipsoidal absorption correction (Tmin
)
0.755; Tmax) 0.841; merging Rint before/after correction )
0.0334/0.0302) were performed using XPREP.27 Of the 9928
reflections measured, 3479 were unique and 3039 had I > 3σ(I)
and were used in the refinement. Redundant reflections were
averaged. The data were corrected for Lorentz and polariza-
tion effects, but no correction for crystal decay was applied.
The structure was solved by direct methods using the TEXSAN
software package28 on a Digital microvax workstation and
refined using standard least-squares and Fourier techniques.
A conformational disorder involving V and the N(2) amide
ligand across a virtual mirror plane passing through N(1),
N(2), and Cl(2) was refined, resulting in partial occupancies
of 0.844 for V(1), Si(3), Si(4), and C(8). The occupancies of
V(2), Si(5), Si(6), and Cl(3) were constrained to sum to full
occupancy. The position of the low-occupancy carbon atom
near Cl(1) was not resolved. All of the full occupancy non-
hydrogen atoms were refined with anisotropic thermal pa-
rameters. Hydrogen atoms for the ordered -N(SiMe3)2 group
were fixed at idealized positions (C-H ) 0.95 Å). Assignment
of the correct enantiomorph was indicated by refinement of
the Flack parameter to -0.0404(83). Neutral atomic scatter-
ing factors were taken from Cromer and Waber,29 and anoma-
lous dispersion effects30 were included in Fc. The final
residuals for 202 variables refined against 3039 data for which
I > 3σ(I) were R ) 0.0381, Rw ) 0.0570, and GOF ) 2.083.
[Li(TMEDA)2]{[(Me3Si)2N]2VCl2}. Data collection and
integration were carried out as described above. The space
group P21/c (No. 14) was uniquely defined by the systematic
Meth od B. A C6D6 solution (ca. 0.5 mL) of {[(Me3Si)2N]2-
VMe}2(µ-O) (22.5 mg, 0.0285 mmol) in a Teflon sealable NMR
tube was treated with PhCH(O)CH2 (3.2 µL, 0.028 mmol). After
24 h, the initially green mixture was clear yellow. Analysis
1
by H NMR spectroscopy showed only styrene and [(Me3Si)2-
N]2V(O)(Me). 1H NMR: δ 1.29 (s, 3H, V-Me, ∆ν1/2 ca. 25 Hz),
0.39 (s, 36H, SiMe3). 51V NMR (78.94 MHz): δ 222 (∆ν1/2 ca.
180 Hz). IR: 1251 (vs), 1093 (w br), 1014 (s, νVdO), 900 (s),
846 (vs), 794 (s), 766 (m), 719 (s), 677 (m), 646 (m), 620 (w),
588 (w br), 523 (w), 461 w cm-1
.
[(Me3Si)2N]2V(O)(P h ). THF (20 mL) was added to a
mixture of [(Me3Si)2N]2VCl(THF) (0.45 g, 0.94 mmol) and
MgPh2 (84 mg, 0.47 mmol), giving a deep blue solution. After
10 min, PhCH(O)CH2 (130 µL, 1.14 mmol) was added. The
solution at first became green, but over a few seconds it turned
clear orange. After 5 min, the volatile materials were removed
under reduced pressure, leaving an orange oily residue.
Extraction with hexanes (50 mL), filteration of the extract
through a frit padded with Celite, and removal of the solvent
under vacuum left the product as a dark orange-red oil (355
mg, 81%). 1H NMR: δ 7.78 (s, 2H, o-Ph), 6.97 (m, 3H, m- and
p-Ph), 0.38 (s, 36H, -SiMe3). 51V NMR (78.94 MHz): δ 101
(∆ν1/2 ca. 235 Hz). IR (KBr, neat): 1422 (m), 1405 (m), 1253
(vs), 1113 (m), 1060 (m), 1011 (s), 994 (m), 950 (m), 847 (vs),
766 (m), 720 (s), 694 (m), 677 (m), 646 (m), 620 (w) cm-1
.
[(Me3Si)2N]2V(Cl)(N2CP h 2). A hexanes solution (40 mL)
of [(Me3Si)2N]2VCl(THF) (1.41 g, 2.94 mmol) was added to a
flask containing Ph2CN2 (570 mg, 2.93 mmol), resulting in a
dark orange-red mixture. After the mixture was stirred for 5
min, the volatile materials were removed under reduced
pressure, leaving a sticky residue. Extraction with MeCN (60
mL) and then THF (60 mL) was followed by filtration and
concentration of the combined extracts to ca. 20 mL. Cooling
the mixture to -25 °C for several days afforded dark red-brown
crystals (442 mg, 25%), which were isolated by filtration and
dried under vacuum. Mp: 91-95 °C (dec). 1H NMR (400
MHz, 22 °C): δ 7.69 (“d of d”, 4H, o-Ph and o-Ph′), 7.25 (t, 2H,
J ) 7.6 Hz, m-Ph), 7.10 (t, 1H, J ) 7.4 Hz, p-Ph), 7.02 (m, 3H,
m- and p-Ph′), 0.42 (s, 36H, -SiMe3). 1H NMR (400 MHz, 97
(25) SMART Area-Detector Software Package; Siemens Industrial
Automation, Inc.: Madison, WI, 1993.
(26) SAINT: SAX Area-Detector Integration Program, version 4.024;
Siemens Industrial Automation, Inc.: Madison, WI, 1994.
(27) XPREP: Part of the SHELXTL Crystal Structure Determination
Package; Siemens Industrial Automation: Madison, WI, 1994.
(28) TEXSAN: Crystal Structure Analysis Package; Molecular
Structure Corp.: 1992.
(29) Cromer, D. T.; Waber, J . T. International Tables for X-ray
Crystallography; The Kynoch Press: Birmingham, England, 1974; Vol.
IV, Table 2.2B.
(30) Cromer, D. T.; Waber, J . T. International Tables for X-ray
Crystallography; The Kynoch Press: Birmingham, England, 1974; Vol.
IV, Table 2.3.1.

Oxidation Reactions of [(Me3Si)2N]2VX(THF)
Organometallics, Vol. 16, No. 24, 1997 5151
Ta ble 1. Su m m a r y of X-r a y Diffr a ction Da ta : [N] ) N(SiMe3)2; [Li] ) Li(TMEDA)2
[N]2VCl2
[Li]{[N]2VCl2}
[Li]{[N]2VMe2}
C26H74LiN6Si4V
641.14
[N]2VCl(N2CPh2)
C25H46ClN4Si4V
formula
mol wt
C12H36Cl2N2Si4V
442.62
C24H68Cl2LiN6Si4V
681.97
601.40
source, color, habit
cryst size (mm)
cryst syst
space group
T (°C)
a (Å)
b (Å)
c (Å)
MeCN, red, tabular
0.36 × 0.25 × 0.13
orthorhombic
P212121
hexanes, purple, acicular ether, blue, equant
hexanes, red-brown, equant
0.39 × 0.35 × 0.25
monoclinic
P21/c
0.49 × 0.35 × 0.30
monoclinic
P21/c
0.34 × 0.30 × 0.28
monoclinic
P21/n
-145
-157
-122
-117
12.5250(2)
13.2145(1)
14.6238(3)
90
19.2175(2)
22.4030(1)
19.4357(3)
90
21.2683(1)
13.5551(2)
29.0793(2)
90
9.4017(3)
32.088(6)
11.5636(3)
90
R (deg)
â (deg)
90
90
96.749(1)
90
93.113(1)
90
107.050(1)
90
3335.23(23)
4
1.20
5.41
Siemens, CCD/
area detector
Mo KR (0.710 73 Å)
ω (0.3° scans)
hemisphere
14 090
γ (deg)
vol (Å3)
Z
2420.40(8)
4
1.22
8309.61(15)
8
8371.00(25)
8
Fcalcd (g cm-3
)
1.00
1.02
µ (cm-1
)
8.25
4.44
3.73
diffractometer
Siemens, CCD/
area detector
Mo KR (0.710 73 Å)
ω (0.3° scans)
hemisphere
9928
Siemens, CCD/
area detector
Mo KR (0.710 73 Å)
ω (0.3° scans)
hemisphere
34 748
Siemens, CCD/
area detector
Mo KR (0.710 73 Å)
ω (0.3° scans)
hemisphere
34 349
radiation (λ)
scan mode
collcn range
total no. of reflcns
no. of unique reflns
Rint
3479
0.038
12 274
12 508
4888
0.0281
0.0327
0.0427
abs type
semiempirical, XPREP
0.755-0.841
semiempirical, XPREP
0.828-0.893
semiempirical, XPREP
0.730-0.885
none
NA
transm coeff
structure soln
no. of obs (no), I > 3σ(I)
direct methods, TEXSAN direct methods, TEXSAN direct methods, TEXSAN direct methods, TEXSAN
3039
8561
685
0.0451, 0.0575
2.051
7259
660
0.0820, 0.1038
3.471
3910
500
0.0298, 0.0421
1.764
no. of params refined (nv) 202
final R,a Rw
0.0381, 0.0570
2.083
b
GOFc
a
b
2
1/2
2
2
R ) [∑||Fo| - |Fc||]/∑|Fo|. Rw ) {[∑w(|Fo| - |Fc|)2]/∑wFo
}
.
c GOF ) [∑w(|Fo| - |Fc| )2/(no - nv)]1/2
.
Ta ble 2. Selected Metr ica l Da ta for Cr ysta llogr a p h ica lly Ch a r a cter ized Com p ou n d s
[(Me3Si)2N]2VCl2 [Li(TMEDA)2]{[(Me3Si)2N]2VCl2} [Li(TMEDA)2]{[(Me3Si)2N]2VMe2} [(Me3Si)2N]2V(Cl)(N2CPh2)
Bond Distances (Å)
2.311(1) V(1)-N(1)
V(1)-N(1)
1.847(4)
1.842(4)
2.211(2)
2.222(2)
1.774(4)
1.796(4)
1.772(4)
1.807(4)
1.84(1)
V(1)-Cl(1)
V(1)-Cl(2)
V(1)-N(1)
V(1)-N(2)
V(2)-Cl(3)
V(2)-Cl(4)
V(2)-N(3)
V(2)-N(4)
Li(1)-Nav
Li(2)-Nav
2.031(6)
2.011(6)
2.096(8)
2.124(8)
1.711(6)
1.722(6)
1.709(6)
1.729(6)
V-Cl
2.2454(7)
1.851(1)
1.879(2)
1.683(2)
1.328(3)
1.295(3)
1.487(4)
1.483(4)
V(1)-N(2)
V(1)-Cl(1)
V(1)-Cl(2)
N(1)-Si(1)
N(1)-Si(2)
N(2)-Si(3)
N(2)-Si(4)
N(2)-Si(5)
N(2)-Si(6)
2.309(1)
1.936(3)
1.949(3)
2.299(1)
2.306(1)
1.946(3)
1.949(3)
2.13(1)
V(1)-N(2)
V(1)-C(1)
V(1)-C(2)
N(1)-Si(1)
N(1)-Si(2)
N(2)-Si(3)
N(2)-Si(4)
V-N(1)
V-N(2)
V-N(3)
N(3)-N(4)
N(4)-C(13)
C(13)-C(14)
C(13)-C20)
1.75(1)
2.13(2)
Bond Angles (deg)
N(1)-V(1)-N(2)
N(1)-V(1)-Cl(1)
N(1)-V(1)-Cl(2)
N(2)-V(1)-Cl(1)
N(2)-V(1)-Cl(2)
118.5(2)
103.1(1)
111.2(1)
113.0(1)
102.2(1)
Cl(1)-V(1)-Cl(2)
Cl(1)-V(1)-N(1)
Cl(1)-V(1)-N(2)
Cl(2)-V(1)-N(1)
Cl(2)-V(1)-N(2)
103.42(5)
109.1(1)
107.5(1)
103.2(1)
114.5(1)
118.0(1)
N(1)-V(1)-N(2)
N(1)-V(1)-C(1)
N(1)-V(1)-Cl2)
N(2)-V(1)-C(1)
N(2)-V(1)-C(2)
C(1)-V(1)-C(2)
124.0(2)
101.4(3)
111.2(3)
112.5(3)
104.0(3)
101.8(3)
Cl-V-N(1)
Cl-V-N(2)
Cl-V-N(3)
N(1)-V-N(2)
N(1)-V-N(3)
N(2)-V-N(3)
106.89(7)
113.75(7)
106.10(7)
117.79(9)
105.5(1)
105.9(1)
Cl(1)-V(1)-Cl(2) 108.83(7) N(1)-V(1)-N(2)
absences. The structure was solved and refined as above. The
final residuals for 685 variables refined against 8561 data for
which I > 3σ(I) were R ) 0.0451, Rw ) 0.0575, and GOF )
2.051.
tropic thermal parameters. Hydrogen atoms were included
on the three ordered -N(SiMe3)2 ligands and on the TMEDA
ligands at idealized positions. The final residuals for 660
variables refined against 7259 data for which I > 3σ(I) were
R ) 0.0820, Rw ) 0.1038, and GOF ) 3.471.
[(Me3Si)2N]2VCl(N2CP h 2). All aspects, from data collec-
tion to solution and refinement of the structure, were as
described above. The space group P21/n (No. 14) was uniquely
defined by the systematic absences. All non-hydrogen atoms
were refined with anisotropic thermal parameters; hydrogen
atoms were located and refined with isotropic thermal param-
eters. The final residuals for 500 variables refined against
3910 data for which I > 3σ(I) were R ) 0.0298, Rw ) 0.0421,
and GOF ) 1.764.
[Li(TMEDA)2]{[(Me3Si)2N]2VMe2}. All aspects, from data
collection to solution and refinement of the structure, were as
described above. The space group P21/c was uniquely defined
by the systematic absences. The molecule crystallized as well-
separated cations and anions with two molecules per asym-
metric unit (Z ) 8). In one of the anions, there existed a
conformational disorder (analogous to that described for
[(Me3Si)2N]2VCl2) across a virtual mirror plane defined ap-
proximately by N(7), N(8), and the midpoint of the vector
joining V(2) and V(3). A model employing major (75%) and
minor (25%) conformations was employed with moderate
success, as indicated by the final agreement factors. The
Li(TMEDA) cations and the ordered anion were well-behaved.
All non-hydrogen atoms (except the silicon and carbon atoms
of the disordered -N(SiMe3)2 ligand) were refined with aniso-
Resu lts a n d Discu ssion
Neu tr a l V(IV) Sp ecies. Drawing from established
research on vanadocene systems, where Cp2VCl2 may

5152 Organometallics, Vol. 16, No. 24, 1997
Gerlach and Arnold
Sch em e 1
be obtained31 by reaction of Cp2VCl with CuCl, [(Me3Si)2-
N]2VCl(THF) underwent one-electron oxidation by CuCl
to yield [(Me3Si)2N]2VCl2 (Scheme 1). Likewise, [(Me3Si)2-
N]2VR(THF) (R ) Me, Ph32) reacted with CuCl to yield
the methyl-chloride and phenyl-chloride V(IV) orga-
nometallic products (Scheme 1). We note that Cp2V(Cl)-
(Me) is the lone example of a mixed halide-hydrocarbyl
that is stable within the Cp2V ligand system.33,34
The redox reactions proceeded rapidly in THF, as a
color change from blue to red along with precipitation
of elemental copper were immediately apparent on
mixing the reactants. The red products are exceedingly
soluble in hydrocarbons and were crystallized from
MeCN to afford the first crops of material in 40-60%
yields. This latter point highlights the decreased reac-
tivity of these V(IV) hydrocarbyls relative to V(III)
species of the type [(Me3Si)2N]2VRL which rapidly add
their V-C bonds across the C-N bonds of both nitriles
and isocyanides.13,35 Solution-state magnetic moments
of 1.7 µB are indicative of a d1electronic configuration
and are consistent with the products as formulated. The
X-ray crystal structure of [(Me3Si)2N]2VCl2 has been
determined (see below). Similar to other structurally
characterized early metal -N(SiMe3)2 complexes, the
amides are planar at nitrogen, indicating that they are
probably acting as three-electron donors (1σ + 2π)
toward the metal center, resulting in a formal electron
count about the vanadium of 13 in these species.36
Since reactions between VCl4 and strong alkylating
reagents can be highly dependent on the reaction
conditions and countercations, we view these transfor-
mations as mild, oxidative routes to (R2N)2VX2 or
(R2N)2VXR vanadium(IV) species that may not be
cleanly obtainable from reactions of V(IV) sources with
highly reducing -NR2 anions. Hoffman and co-workers
have reported congeneric group 5 species that are
obtained using different synthetic methodologies. The
Nb(IV) dihalide [(Me3Si)2N]2NbCl2,14,15 available from
NbCl4(THF)2 and LiN(SiMe3)2, may be converted to
[(Me3Si)2N]2Nb(Cl)(Ph)37 on treatment with ZnPh2.
38
Reduction of Andersen’s [(Me3Si)2N]2TaCl3 with Na/
16,17
Hg affords [(Me3Si)2N]2TaCl2
in 64% yield. It is
noteworthy that bis(amide)titanium(IV) alkyl iodides
have recently been prepared by substitution of a -NMe2
with I or by monoalkylation of a bis(amide)titanium(IV)
diiodide.39
We assume the mechanism of the above reactions
involves initial oxidation of [(Me3Si)2N]2VX(THF) (X )
Cl, Me, Ph) to {[(Me3Si)2N]2VX(THF)}+, followed by an
associative displacement of THF by chloride. In an
attempt to synthesize cationic {[(Me3Si)2N]2VMe(THF)}+
by using a less nucleophilic anion, a THF solution of
the neutral V(III)-methyl was treated with AgBPh4 in
THF. Although the reaction was immediate, a pure
(31) Gladyshev, E. N.; Bayushkin, P. Y.; Cherkasov, V. K.; Sokolov,
V. S. Bull. Acad. Sci. USSR, Div. Chem. Sci. 1979, 28, 1070.
(32) Although the V(III)-Ph complex could not be isolated as a
stable solid, persistent blue solutions formed from the reaction of
[(Me3Si)2N]2VCl(THF) and 0.5 equiv of MgPh2 in THF behave as if
they contain “[(Me3Si)2N]2VPh(THF)”. It is likely that the instability
of the complex stems from facile dissociation of THF followed by
metallation of a -N(SiMe3)2 ligand. Gerlach, C. P.; Arnold, J . Manu-
script in preparation.
(33) Razuvaev, G. A.; Korneva, S. P.; Vyshinskaya, L. I.; Mar’in, V.
P.; Cherkasov, V. K. Bull. Acad. Sci. USSR, Div. Chem. Sci. 1978, 27,
605.
(34) Razuvaev, G. A.; Bayushkin, P. Y.; Cherkasov, V. K.; Gladyshev,
E. N.; Phokeev, A. P. Inorg. Chim. Acta 1980, 44, L103.
(35) Gerlach, C. P.; Arnold, J . Manuscript in preparation.
(36) The covalent convention is followed in counting electrons. See:
Crabtree, R. H. The Organometallic Chemistry of the Elements, 2nd
ed.; Wiley: New York, 1994.
(37) Bott, S. G.; Hoffman, D. M.; Rangarajan, S. P. J . Chem. Soc.,
Dalton Trans. 1996, 1979.
(38) Andersen, R. A. Inorg. Chem. 1979, 18, 3622.
(39) J ohnson, A. R.; Davis, W. M.; Cummins, C. C. Organometallics
1996, 15, 3825.
(40) While a persistent color change from green-blue to blue was
observed on treating [(Me3Si)2N]2VCl(THF) with sources of Et-, we
have no evidence that indicates the identity of the product one way or
another and have not been successful in isolating either a product or
product-derivative from these mixtures.

Oxidation Reactions of [(Me3Si)2N]2VX(THF)
Organometallics, Vol. 16, No. 24, 1997 5153
Sch em e 2
product could not be isolated from the dark brown
mixture. Blue solutions of putative [(Me3Si)2N]2VEt-
(THF),40 from alkylation of [(Me3Si)2N]2VCl(THF) with
EtMgCl or MgEt2, also reacted quickly with CuCl in
THF, but the expected [(Me3Si)2N]2V(Cl)(Et) could not
be isolated. Our inability to isolate either a V(III)- or
V(IV)-alkyl with â-hydrogens in this system may be
compared to the decomposition of Cp2VXR complexes
when the R group contains â-hydrogen atoms.41
[(Me3Si)2N]2VXL. Thus, reaction between [(Me3Si)2N]2-
VCl(THF) and 2 equiv of LiMe in the presence of
TMEDA afforded [Li(TMEDA)2]{[(Me3Si)2N]2VMe2} in
66% yield as highly air-sensitive, deep-blue crystals
(Scheme 1). While the salt formed an oily suspension
in benzene, it was soluble in acetonitrile or ethereal
solvents giving ink-blue solutions. 1H NMR spectra
measured in CD3CN showed sharp signals for the
TMEDA ligand as well as a broad low intensity signal
in the range 2.5-3.0 ppm, presumably for the anionic
portion of the molecule. Magnetic susceptibility mea-
surements made in this same solvent indicated a high
spin d2 electronic configuration (µeff ) 2.57 µB). The
molar conductivity of acetonitrile solutions (ΛM ) 92 S
cm2 mol-1) was in accord with the behavior of a 1:1
electrolyte.43 X-ray quality crystals of the complex were
obtained on recrystallization from diethyl ether, and the
experiment verified our proposed connectivity. The
molecule crystallized as well-separated cations and
anions as discussed below. Variable, low yields of an
extremely air-sensitive, blue, paramagnetic compound
were isolated when the reaction was carried out in the
absence of TMEDA; however, due to the low yield and
irreproducibility of the reaction, characterization of this
material was not possible.
Our initial attempts at synthesizing dialkyl, diaryl,
or mixed alkyl-aryl V(IV) species suggested that the
reactions were solvent and temperature dependent, as
indicated above for alkylations of VCl4. For example,
reaction of [(Me3Si)2N]2VCl2 with MgPh2 in THF at room
temperature (Scheme 2) gave a blue solution that most
likely contained “[(Me3Si)2N]2VPh(THF)”. Work-up of
the reaction mixture in hexanes led to violet mixtures
from which the known42 dimeric {[(Me3Si)2N]V[µ-
CH2SiMe2NSiMe3]}2 was isolated in 55% yield. Given
the crowded coordination sphere about the metal center
in four-coordinate [(Me3Si)2N]2V species, it is likely that
loss of THF in [(Me3Si)2N]2VPh(THF) generates three-
coordinate “[(Me3Si)2N]2VPh”, which then metalates a
-N(SiMe3)2 ligand, loses benzene, and dimerizes. Ad-
dition of pyridine (pyr) to blue solutions of “[(Me3Si)2N]2-
VPh(THF)” formed the stable [(Me3Si)2N]2VPh(pyr)
(Scheme 2), which is more conveniently prepared from
[(Me3Si)2N]2VCl(THF), 0.5 equiv of MgPh2, and pyr.35
In contrast, [(Me3Si)2N]2VCl2 and MgPh2 react in cold
(-60 °C) diethyl ether to give red mixtures that may
contain the V(IV)-diphenyl complex; unfortunately,
extreme solubility in hydrocarbon solvents has ham-
pered adequate purification and characterization of the
material (the compound separates from MeCN as an oil).
Difficulties have also been noted in attempts to prepare
Ta(IV) dialkyls from [(Me3Si)2N]2TaCl2;17 nonetheless,
the synthesis of [(Me3Si)2N]2TaPh2 in 65% yield was
successful. Thus, as a class of compounds, d1 [(Me3Si)2-
N]2MR2 species remain rare.
Attempts to extract hydride from {[(Me3Si)2N]2VMe2}-
to give the V(V) methyl-methylidene complex with
Ph3CPF6 or Et3OBF4 led to an as yet uncharacterized
paramagnetic product in the first case and no reaction
in the second.44 Reaction with B(C6F5)3 in C6D6 appar-
ently led to abstraction of Me- to generate the unstable
intermediate [(Me3Si)2N]2VMe, which, via metalation of
a bis(silyl)amide ligand and loss of CH4, gave dimeric
{[(Me3Si)2N]V[[µ-CH2SiMe2N(SiMe3)]}2 as the only de-
1
tectable product by H NMR spectroscopy.45
Attempts to prepare a lithiated vanadium acetylide
in one step by reaction of Li2C2 wtih [(Me3Si)2N]2-
VCl(THF) led instead to the dichloride anion analog of
the dimethyl complex discussed above. Purple needles
V(III) An ion s. Given the stability of the 14-electron
species [(Me3Si)2N]2VXL, it seemed reasonable that 14-
electron V(III) anions of the type {[(Me3Si)2N]2VX2}-
would be accessible via the one-electron reduction of
[(Me3Si)2N]2VX2 or by nucleophilic attack of X- on
(43) Angelici, R. J . Synthesis and Technique in Inorganic Chemistry;
University Science Books: Mill Valley, CA, 1986.
(44) Conversely, the extraction of H+ from cationic transition metal
dimethyl complexes has successfully been used to synthesize methyl-
methylidene complexes. See: Schrock, R. R. Acc. Chem. Res. 1979, 12,
98. Dawson, D. Y.; Arnold, J . Organometallics 1997, 16, 1111.
(45) Although the dimer is paramagnetic, C6D6 solutions show
several low-intensity resonances in the 1H NMR spectrum that are
indicative of the complex. 1H NMR (300 MHz, C6D6): δ 0.96, 0.64, 0.39,
0.21, -1.2.
(41) Sustmannn, R.; Kopp, G. J . Organomet. Chem. 1988, 347, 325.
(42) Berno, P.; Minhas, R.; Hao, S.; Gambarotta, S. Organometallics
1994, 13, 1052.

5154 Organometallics, Vol. 16, No. 24, 1997
Gerlach and Arnold
Sch em e 3
of [Li(TMEDA)2]{[(Me3Si)2N]2VCl2} were isolated in
40% yield based on vanadium from the reaction of
[(Me3Si)2N]2VCl(THF) with 1 equiv of Li2C2(THF)x in
the presence of TMEDA. Recrystallization of the com-
plex from diethyl ether afforded purple, prismatic
crystals which dissolved in hydrocarbon solvents to give
blue solutions. In the absence of TMEDA, the reaction
was messy and it is clear that the presence of the
diamine assists in the chloride redistribution that has
taken place during the course of the reaction. The
lithium reduction of [(Me3Si)2N]2VCl2 in the presence
of TMEDA also yielded the dichloride anion, although
the product was not as clean as that isolated from the
above route.
eventually clear yellow. Removal of the solvent yields
[(Me3Si)2N]2V(O)(Me) as a dark-orange oil. Monitoring
the reaction by H NMR spectroscopy (C6D6) showed a
1
broad signal at δ 1.85 that we attribute to the green
intermediate (see below), which over several hours gave
way to only signals for free styrene and [(Me3Si)2N]2V-
(O)(Me). The oxo-methyl complex was characterized
by a sharp singlet at δ 0.39 for the -SiMe3 groups and
a singlet at δ 1.29 (∆ν1/2 ) 25 Hz) for the methyl group,
broadened due to coupling to the quadropolar 51V
7
nucleus (I ) /2). A singlet in the 51V NMR spectrum
at δ 222 is consistent with a +5 oxidation state of the
vanadium, and we assign a strong absorbance in the
IR spectrum at 1014 cm-1 to the νVdO
.
In contrast to the low solubility of the dimethyl anion,
the dichloride salt dissolves in benzene, giving a solution
magnetic moment of 2.64 µB at ambient temperature.
Conductivity measurements indicated that it is a 1:1
electrolyte in acetonitrile (ΛM ) 92 S cm2 mol-1). In
The green intermediate was isolated cleanly from
preparative-scale reactions between (i) 0.5 equiv of
styrene oxide and [(Me3Si)2N]2VMe(THF) (Scheme 3) or
(ii) [(Me3Si)2N]2VMe(THF) and [(Me3Si)2N]2V(O)(Me).
The µ-O dimer is converted smoothly to [(Me3Si)2N]2-
V(O)(Me) on treatment with an additional equivalent
of styrene oxide. Although extremely soluble in hex-
anes, the dimer crystallized nicely from HMDSO (65%)
and the crystal structure confirmed the connectivity.13
We tentatively assign a strong absorbance at 709 cm-1
in the IR spectrum to the linear V-O-V unit. The
dimer is paramagnetic, and its magnetic moment of 2.46
µB (1.74 µB per V) indicates that, at least at room
temperature in solution, there is negligible coupling of
the unpaired spins and that the µ-oxo core is best
described as bridging two V(IV), d1 centers. Crystal-
lographic data also rules out a mixed valence ground
state, i.e., a V(V) oxo acting as a dative donor to a V(III)
center, as the molecule crystallized with a C2-axis
passing through the µ-O resulting in one independent
V-O distance of 1.7943(4) Å.13 This contrasts with the
µ-N derivatives of vanadium, which may possess both
long and short V-N bonds,48-51 and also with
[Cp2TaMe]2(µ-S),52 which is described as diamagnetic
and possibly in equilibrium with Cp2Ta(Me)(S) and
“Cp2TaMe”, i.e., Ta(V) and Ta(III) species. A broad
1
contrast to the H NMR spectrum measured in C6D6,
which showed two broadened signals at ca. 5.0 and 1.9
ppm, in CD3CN sharp signals for the Li(TMEDA)2
cation were observed at δ 2.32 (CH2) and 2.17 (CH3),
along with a broadened signal (∆ν1/2 ca. 200 Hz)
centered at ca. δ 2.8 for the anion. A crystallographic
study (see below) verified the proposed connectivity
shown in Scheme 1. We note that related “ate” com-
plexes of Ti(III) have recently been reported where the
Cl and Me ligands form bridges between bis(amide)ti-
tanium and Li(TMEDA) units.39,46 The successful isola-
tion of bis(amide)Ti and bis(amide)V halide ate com-
plexes may be contrasted with the metallocene systems,
where [Cp2MCl2]- (M ) Ti, V) and [Cp2VCl]- are rapidly
susceptible to loss of Cl-.47
Oxid a tion s w ith P h CH(O)CH2. We have previ-
ously shown that the V(III) bromide derivative [(Me3Si)2-
N]2VBr(THF) reacts with styrene oxide to yield [(Me3Si)2-
N]2V(O)(Br) as the kinetic product.12 Curious as to
whether organovanadium oxo complexes could be pre-
pared in a similar manner, we investigated the reaction
between [(Me3Si)2N]2VR(THF) (R ) Me, Ph) and styrene
oxide.
1
signal at δ 1.85 in the H NMR spectrum of the isolated
material matches that for the observed intermediate in
Treatment of a hexanes solution of [(Me3Si)2N]2VMe-
(THF) with 1 equiv of styrene oxide (Scheme 3) resulted
in an immediate color change from blue to green and
(48) Critchlow, S. C.; Lerchen, M. E.; Smith, R. C.; Doherty, N. M.
J . Am. Chem. Soc. 1988, 110, 8071.
(49) Sorensen, K. L.; Lerchen, M. E.; Ziller, J . W.; Doherty, N. M.
Inorg. Chem. 1992, 31, 2678.
(46) Scoles, L.; Minhas, R.; Duchateau, R.; J ubb, J .; Gambarotta,
S. Organometallics 1994, 13, 4978.
(47) Mugnier, Y.; Moise, C.; Laviron, E. Nouv. J . Chim. 1982, 6,
197.
(50) Willing, W.; Christophersen, R.; Muller, U.; Dehnicke, K. Z.
Anorg. Allg. Chem. 1987, 555, 16.
(51) Sable, D. B.; Armstrong, W. H. Inorg. Chem. 1992, 31, 161.
(52) Proulx, G.; Bergman, R. G. Organometallics 1996, 15, 133.

Oxidation Reactions of [(Me3Si)2N]2VX(THF)
Organometallics, Vol. 16, No. 24, 1997 5155
the one-step transformation of [(Me3Si)2N]2VMe(THF)
to [(Me3Si)2N]2V(O)(Me).
In regard to the kinetics of the reactions in Scheme
3, once [(Me3Si)2N]2V(O)(Me) is formed it must react
with [(Me3Si)2N]2VMe(THF) faster than does styrene
oxide. Nucleophilic addition of vanadium(V) oxo com-
plexes to unsaturated Ti53 species has recently been
studied by Cummins and co-workers, and there is also
precedent for this type of reaction between two vana-
dium centers in the literature.54
While the reaction of 0.5 equiv of styrene oxide with
[(Me3Si)2N]2VPh(THF) gave persistent green mixtures,
on workup the color changed to brown and the putative
{[(Me3Si)2N]2VPh}2(µ-O) was not isolated. However,
treatment of [(Me3Si)2N]2VPh(THF) with a full equiva-
lent of styrene oxide yielded [(Me3Si)2N]2V(O)(Ph) as a
dark red-orange oil in 81% yield (eq 1). 1H and 51V NMR
data are consistent this formulation, and a strong
absorbance at 1011 cm-1 in the IR spectrum is indica-
tive of a terminal VdO functionality. At this point, we
have no reasonable explanation for why an intermediate
{[(Me3Si)2N]2VPh}2(µ-O) does not appear to be stable
in the solid state, and attempts to isolate [(Me3Si)2N]2-
VMe(µ-O)VPh[N(SiMe3)2]2 by reaction of [(Me3Si)2N]2V-
(O)(R) with [(Me3Si)2N]2VR′(THF) were also unsuccess-
ful.
Rea ction of [(Me3Si)2N]2VCl(THF ) w ith P h 2CN2.
Reaction of [(Me3Si)2N]2VCl(THF) with diphenyldiazo-
methane in hexanes gave a deep-red solution from
which [(Me3Si)2N]2V(Cl)(N2CPh2) was isolated (eq 2).
F igu r e 1. ORTEP drawing (50% ellipsoids) of [(Me3Si)2-
N]2VCl2. V(2), Si(5), Si(6), and Cl(3) are at 16% occupancy,
while V(1), Si(3), Si(4), and C(8) are at 84% occupancy. The
position of the (minor occupancy) carbon atom near Cl(1)
was not resolved.
nized as precursors to alkylidenes via loss of dinitro-
gen,56-59 no evidence for this type of reactivity was found
in the present case. [(Me3Si)2N]2V(Cl)(N2CPh2) showed
no sign of decomposition in C6D6, even after prolonged
periods of heating (>100 °C) or photolysis. Reaction
between (i) [(Me3Si)2N]2VMe(THF) and Me3SiCHN2 or
Ph2CN2 or (ii) [(Me3Si)2N]2VCl(THF) and Me3SiCHN2
also proceeded rapidly to afford deep red mixtures,
however, in these cases the products could not be
isolated as crystalline solids and appear to be very low
melting materials that were difficult to isolate and
purify in good yields.
X-r a y Cr ysta l Str u ctu r es. [(Me3Si)2N]2VCl2. Se-
lected bond distances and angles for this as well as the
other crystallographically characterized compounds are
collected in Table 2. As described in the Experimental
Section, the molecule crystallized as a mixture of major
(85%) and minor (15%) conformers that are related by
a virtual mirror plane that passes roughly through the
amide nitrogens, Cl(2), C(10), and the midpoint of the
vector that connects the two partial occupancy vana-
dium nuclei. This is illustrated in Figure 1, which
includes all full and partial occupancy atoms. The
following points refer to the major conformer, of which
an ORTEP drawing is shown in Figure 2. The VNSi2
units are virtually planar, with all of the angles about
The compound is extremely soluble in hydrocarbon
solvents, but crystallization from a mixture of MeCN/
THF afforded a crop of analytically pure material in 30%
yield. X-ray structural data (see below) suggest that
the vanadium center has been oxidized to the +5 state
concomitant with a two-electron reduction of the diazo-
alkane moiety to an alkylidenehydrazido.55 Sharp
resonances in the 1H, 13C{1H}, and 51V NMR spectra
also indicate the species is best described as a d0,
diamagnetic compound.
A signal for the diazo-bound carbon was observed in
the 13C{1H} NMR spectrum at δ 157.5. The aryl carbon
signals for the two phenyl rings are inequivalent at
room temperature (i.e., Ph and Ph′), indicating a slow
rotation about one or more of the bonds in the VdN-
NdCPh2 unit. On warming the sample, the signals
coalesced at 55 °C. Further heating to 95 °C sharpened
the signals such that a single set of four phenyl 13C
resonances is observed in the spectrum. Although
metallodiazoalkane complexes have long been recog-
(56) Hermann, W. A. Angew. Chem., Int. Ed. Engl. 1978, 17, 800.
(57) Mizobe, Y.; Ishii, Y.; Hidai, M. Coord. Chem. Rev. 1995, 139,
281.
(53) Wanandi, P. W.; Davis, W. B.; Cummins, C. C. J . Am. Chem.
Soc. 1995, 117, 2110.
(54) Ruiz, J .; Vivanco, M.; Floriani, C.; Chiesi-Villa, A.; Guastini,
C. J . Chem. Soc., Chem. Commun. 1991, 762.
(55) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry, 5th
ed.; J ohn Wiley & Sons: New York, 1988.
(58) Polse, J . L.; Andersen, R. A.; Bergman, R. G. J . Am. Chem. Soc.
1996, 118, 8737.
(59) Schwab, P.; Grubbs, R. H.; Ziller, J . W. J . Am. Chem. Soc. 1996,
118, 100.

5156 Organometallics, Vol. 16, No. 24, 1997
Gerlach and Arnold
F igu r e 2. ORTEP drawing (50% ellipsoids) of the major
conformer of [(Me3Si)2N]2VCl2.
F igu r e 3. ORTEP drawing (50% ellipsoids) of one of the
crystallographically independent molecules of {Li(TMEDA)2]-
{[(Me3Si)2N]2VCl2}.
the amide nitrogen being ca. 120°. As in the other
complexes that we have crystallographically studied
that contain the {[(Me3Si)2N]2V}n+ fragment, the largest
angle about the metal center is between the two amide
ligands (N(1)-V(1)-N(2) ) 118.5(2)°). The remainder
of the angles about the metal span the range 102.2(1)°-
113.0(1)° (Table 2). Relative to [(Me3Si)2N]2VCl(THF),19
the V-Cl bond lengths in [(Me3Si)2N]2VCl2 (V(1)-Cl(1)
) 2.211(2) Å; V(1)-Cl(2) ) 2.222(2) Å) are slightly
shorter due to the smaller V(IV) in the present case.
There are some interesting differences between this
vanadium structure and that of [(Me3Si)2N]2TaCl2,16
with which the intermediate niobium complex is appar-
ently isostructural.15 Despite the smaller radius of
V(IV), the distortion of the N2VCl2 core from idealized
C2v symmetry is not nearly as pronounced as that
observed in [(Me3Si)2N]2TaCl2. For example, the dihe-
dral angle between the VN2 and VCl2 deviates by ca. 6°
from the ideal value of 90°, versus a value of 17° in the
Ta analog. Furthermore, the Ta complex possesses a
rather compressed Cl-Ta-Cl angle (95.7(2)°) compared
to a more normal Cl-V-Cl angle of 108.83(7)° in the
major conformer. Equivalent V-N bond lengths (V(1)-
N(1) ) 1.847(4) Å, V(1)-N(2) ) 1.842(4) Å) contrast with
the unsymmetrical Ta-N bond lengths, the latter due
to steric repulsion between a chlorine and amide methyl
groups. On the basis of the wide range of dihedral
angles we have observed between the two N2V planes
in structures having the {[(Me3Si)2N]2V}n+ fragment
(e.g., see below), the apparently soft potential-energy
surface for rotation about the V-N bonds may not exist
in the third-row congener, particularly if N(pπ)-M(dπ)
overlap assists in “locking” the amides in a particular
conformation. In other words, facile rotation about V-N
bonds in complexes of {[(Me3Si)2N]2V}n+ may allow the
molecules to avoid unfavorable, intramolecular steric
repulsions in the solid state. A shallow potential-energy
curve for bending the Nb-N-Si angles in [(Me3Si)2-
N]2NbBr2 has been noted, a point perhaps related to the
ability of the -N(SiMe3)2 ligand to metalate via γ-hy-
drogen elimination.
F igu r e 4. ORTEP drawing (50% ellipsoids) of one of the
crystallographically independent molecules of [Li(TMEDA)2]-
{[(Me3Si)2N]2VMe2}.
by ca. 0.1 Å when compared with those of neutral
[(Me3Si)2N]2VCl2 above and, as expected, are slightly
shorter than those in the analogous Ti species.60,61 The
angles about the vanadium center are virtually identical
in the two crystallographically independent molecules,
however, a subtle difference between the anions exists.
While the -N(SiMe3)2 groups are all planar at nitrogen,
the dihedral angle between the two VNSi2 planes
measures 99° in the V(1) anion versus a value of 83° in
the V(2) anion, again indicative of a low activation
energy for rotation about the V-N bonds in this system.
[Li(TMEDA)2]{[(Me3Si)2N]2VMe2}. The molecule
crystallized in the same manner as the dichloride above,
i.e., in P21/c with two molecules per asymmetric unit.
Diffraction data verified the connectivity in the para-
magnetic molecule, but a severe disorder in one of the
anions (analogous to that described for [(Me3Si)2N]2VCl2,
but not nearly as well-behaved) limits the usefulness
of the metrical data. An ORTEP view of the ordered
molecule is shown in Figure 4. The dihedral angle
between the VNSi2 planes is 96°, close to that observed
in the V(1) anion of [Li(TMEDA)2]{[(Me3Si)2N]2VCl2} to
which the present structure is closely related. The V-C
bond lengths in the ordered anion (V(1)-C(1) ) 2.096(8)
[Li(TMEDA)2]{[(Me3Si)2N]2VCl2}. The molecule
crystallized as well-separated cations and anions, the
closest intramolecular contact (excluding hydrogen at-
oms) being the C(9)-C(30) distance of 3.333(7) Å. There
are two molecules per asymmetric unit, and an ORTEP
drawing of one of them is shown in Figure 3. The
metrical parameters of the Li(TMEDA) cations are
unremarkable. The vanadium-ligand bond lengths (V-
Nav ) 1.945(5) Å, V-Clav ) 2.306(2) Å) are elongated
(60) Beydoun, N.; Duchateau, R.; Gambarotta, S. J . Chem. Soc.,
Chem. Commun. 1992, 244.
(61) Duchateau, R.; Gambarotta, S.; Beydoun, N.; Bensimon, C. J .
Am. Chem. Soc. 1991, 113, 8986.

Oxidation Reactions of [(Me3Si)2N]2VX(THF)
Organometallics, Vol. 16, No. 24, 1997 5157
Å) is as expected for a NdC double bond.67 Along with
the N(3)-N(4)-C(13) angle of 121.9(2)°, which indicates
sp2 hybridization of N(4), it follows that the best Lewis
structure is resonance structure A, shown below, with
a smaller contribution from B. Of the numerous bind-
ing modes that have been well-documented for transi-
tion metal diazoalkane complexes,68 this doubly-bent
form is rare;57 the other example being Mo2(OPri)6-
(N2CPh2)2(py)69 whose solid-state structure features
Mo-N-N angles of 155(1)° and 164(1)°, with corre-
sponding N-N-C angles of 124(1)° and 122(1)°.
Su m m a r y. We have demonstrated that V(III) spe-
cies of the type [(Me3Si)2N]2VX(THF) are easily oxidized
by CuCl to give [(Me3Si)2N]2V(Cl)(X) products. As in
alkylation reactions of Cp2VCl2, attempts to use these
V(IV) compounds as the starting material for bis(hy-
drocarbyl) complexes of V(IV) showed that care must
be taken in order to minimize reduction of the metal.
Styrene oxide affects the two-electron oxidation of
[(Me3Si)2N]2VR(THF) (R ) Me, Ph), and in the case of
R ) Me, it was shown that the reaction proceeded
through a dimeric V(IV) intermediate bridged by a
single O2- ligand. Barring a trimolecular transfer of
oxygen from the epoxide to two V(III) centers, the
formation and lifetime of {[(Me3Si)2N]2VMe}2(µ-O) in
the presence of excess PhCH(O)CH2 suggests that
nucleophilic addition of [(Me3Si)2N]2V(O)(Me) to [(Me3Si)2-
N]2VMe(THF) is faster than than the transfer of oxygen
from PhCH(O)CH2 to [(Me3Si)2N]2VMe(THF). In a
related oxidation reaction, Ph2CN2 was formally reduced
F igu r e 5. ORTEP drawing (50% ellipsoids) of [(Me3Si)2-
N]2V(Cl)(N2CPh2).
Å, V(1)-C(2) ) 2.124(8) Å) are the same within experi-
mental error as that in the neutral V(III) complex
[(Me3Si)2N]2VMe(THF).13
[(Me3Si)2N]2VCl(N2CP h 2). An ORTEP drawing of
the structure is shown in Figure 5. The distorted
tetrahedral geometry about the metal is such that the
angle between the amide nitrogens and vanadium is
117.79(9)° and that between the N-bound Ph2CN2 and
the remaining three ligands are all ca. 106°. The sum
of the angles about N(1) (357.5(2)°) and N(2) (358.3(2)°)
again establish planarity at nitrogen for the amide
ligands. The V-N(1), V-N(2), and V-Cl bond lengths
(1.851(2), 1.879(2), and 2.2454(7) Å, respectively) are all
unremarkable.
The most interesting structural feature is the geom-
etry of the coordinated Ph2CN2 ligand. Consistent with
a reduction of the diazoalkane to a Ph2CN22- ligand, or
alkylidenehydrazido, is the short V-N(3) bond length
of 1.683(2) Å. Although marginally longer, the V-N(3)
distance is comparable to the V-N triple bonds found
in other four-coordinate, V(V) imido complexes, such as
(Ph3SiS)3VdNBut (V-N ) 1.622(2) Å, V-N-C )
170.7(2)°),62 (Me3SiO)3VdNAdm (Adm ) adamantyl;
V-N ) 1.614(2), V-N-C ) 175.8(2)°),63 Me3SiNdVCl3
(V-N ) 1.59(1) Å, V-N-Si ) 177.5(7)°),64 and (RArFN)2-
VI(dNMes) (R ) C(CD3)2Me, ArF ) 2,5-C6H3FMe, Mes
) 2,4,6-C6H2Me3; V-N ) 1.645(7) Å, V-N-C )
175.7(7)°).65 In view of the large distortion of the
V-N(3)-N(4) angle (152.8(2)°) from 180°, the VdN-
linkage is analogous to that in a bent imido consisting
of a double bond between the vanadium and nitrogen
(i.e., a two-electron donor). The N(3)-N(4) distance
(1.328(3) Å) is intermediate to a NdN double and N-N
single bond,66 while the N(4)-C(13) distance (1.295(3)
2-
to a Ph2CN2 ligand by [(Me3Si)2N]2VCl(THF) to give
an “alkylidenehydrazido” in which the N2 unit was
neither thermally or photolytically labile under the
conditions we have examined thus far. The crystal
structure of [(Me3Si)2N]2VCl(N2CPh2) showed the
PhCN22- unit bound in a rare, doubly-bent, two-electron
donor mode.
Ack n ow led gm en t. We thank the National Science
Foundation for support and the Alfred P. Sloan Founda-
tion for a fellowship (to J .A.).
Su p p or tin g In for m a tion Ava ila ble: Tables of bond
distances and angles, atomic coordinates, and anisotropic
thermal parameters, packing diagrams for [(Me3Si)2N]2VCl2,
[Li(TMEDA)2]{[(Me3Si)2N]2VCl2}, [Li(TMEDA)2]{[(Me3Si)2N]2-
VMe2}, and [(Me3Si)2N]2VCl(N2CPh2), and an ORTEP drawing
showing the disorder in [Li(TMEDA)2]{[(Me3Si)2N]2VMe2} (47
pages). Ordering information is given on any current mast-
head page.
OM970458I
(62) Preuss, F.; Noichl, H.; Kaub, J . Z. Naturforsch, Teil B 1986,
41, 1085.
(63) Nugent, W. A.; Harlow, R. L. J . Chem. Soc., Chem. Commun.
1979, 342.
(64) Schweda, E.; Scherfise, K. D.; Dehnicke, K. Z. Anorg. Allg.
Chem. 1985, 528, 117.
(67) For comparison, the CdN bond length and CdN-C angle in
triphenylimine is 1.287(1) Å and 120.6(1)°, respectively. See: Tucker,
P. A.; Hoek, A.; ten Cate, J . M.; Vos, A. Acta. Crystallogr., Sect. B 1975,
31, 733.
(65) Fickes, M. G.; Davis, W. B.; Cummins, C. C. J . Am. Chem. Soc.
1995, 117, 6384.
(66) Cotton, F. A.; Wilkinson, G.; Gaus, P. L. Basic Inorganic
Chemistry, 3rd ed.; Wiley: New York, 1995.
(68) Hillhouse, G. L.; Haymore, B. L. J . Am. Chem. Soc. 1982, 104,
1537.
(69) Chisholm, M. H.; Folting, K.; Huffman, J . C.; Ratermann, A.
L. J . Chem. Soc., Chem. Commun. 1981, 1229.