Cationic vanadium(IV) methyl complexes [Cp2VMe(CH3CN)][B(C6H5)4] and [Cp2VMe(THF)][MeB(C6F5)3]

Article abstract of DOI:10.1021/om010894b

The structural establishment of the cationic vanadocene alkyl complex [Cp₂VMe(Ch₃CN)]⁺ with [BPh₄]^- counteranion was presented. The reaction of Cp₂VMe₂ in THF was also described

Full text of DOI:10.1021/om010894b

1124
Organometallics 2002, 21, 1124-1126
Ca tion ic Va n a d iu m (IV) Meth yl Com p lexes
[Cp 2VMe(CH3CN)][B(C6H5)4] a n d
[Cp 2VMe(THF )][MeB(C6F 5)3]
Robert Choukroun,* Christian Lorber, and Bruno Donnadieu
Equipe Pre´curseurs Mole´culaires et Mate´riaux, Laboratoire de Chimie de Coordination,
CNRS UPR 8241, 205 Route de Narbonne, 31077 Toulouse Cedex 4, France
Received October 12, 2001
The cationic vanadocene alkyl complex [Cp2VMe(CH3CN)]+ with [BPh4]- counteranion was
structurally established. The reaction of Cp2VMe2 in THF in the presence of B(C6F5)3 is also
described: EPR evidence of the intermediate formation of the [Cp2VMe(THF)]+ species, which
gives, via a disproportionation redox reaction, the VIII species [Cp2V(THF)][Me B(C6F5)3], is
demonstrated.
The chemistry of cationic complexes of group 4 is very
the other structures already resolved and established
in the Ti and Zr cationic chemistry. On the other hand
the reactivity of 1 with the tris(perfluorophenyl)borane
B(C6F5)3 is hereby presented.
well documented, and literature is abundant concerning
the structural characterization of nearly all these
complexes.1 On the other hand, the chemistry and the
X-ray structure of cationic complexes of vanadium is less
developed2 despite their potential application in Zie-
gler-Natta catalysis. Efforts have been made by our
group to obtain types of cationic vanadium complexes
from the protonolysis of vanadium alkylamido or vana-
dium alkyl complexes with [NHMe2Ph][BR4] (R ) C6H5
or C6F5).3,4 Recently we carried out the reaction between
Cp2VMe2 (1), and [NHMe2Ph][B(C6H5)4] in acetonitrile,
and [Cp2VMe(CH3CN)][B(C6H5)4] was isolated and spec-
troscopically and analytically characterized.4 Its analogy
with the well-known Ti and Zr analogue complexes5-8
as well as its inertness toward ethylene polymerization
in contrast to group 4 led us to ascertain the X-ray
structure of this adduct vanadium complex to ensure
that the formulated complex is sor is notssimilar to
In the course of our studies of the reactivity of [Cp2-
VMe]+, we have recently crystallized [Cp2VMe(CH3CN)]-
[B(C6H5)4] (2), which was confirmed by an X-ray crystal
structure determination (Figure 1). The structure of 2
does not present new features in its tetrahedral struc-
tural geometry. Bond angles around the vanadium atom
give a pseudo-tetrahedral geometry where both planes
[Cp1, V, Cp2] and [N-V-C(3)] are nearly perpendicular
(89.82°). Cyclopentadienyl rings are in a staggered
position. V-C (2.221 Å) and V-N (2.096 Å) distances
are consistent with other complexes containing V-C
and V(NCCH3) units.9-13
Some chemistry of 1 with the tetraphenyl borate
ammonium salt [NHMe2Ph][B(C6H5)4] in THF was
previously published.4 Redox and disproportion reac-
tions were demonstrated, according to Scheme 2. Simi-
lar pathways could be observed in the reaction of 1 with
tris(pentafuorophenyl)borane, B(C6F5), in toluene or
THF, and the reactions can be monitored by EPR and
NMR spectroscopies.
(1) (a) Halterman, R. L. In Metallocenes; Togni, A., Halterman, R.
L., Eds.; Wiley-VCH: New York, 1998; Vol. 1, Chapter 8, p 455. Some
recent contributions: (b) Grimmer, N. E.; Coville, N. J .; De Koning,
C. B.; Smith, J . M.; Cook, L. M. J . Organomet. Chem. 2000, 616, 112.
(c) Thomas, E. J .; Rausch, M. D.; Chien, J . C. W. Organometallics 2000,
19, 5744. (d) Zhang, F.; Mu, Y.; Zhao, L.; Zhang, Y.; Bu, W.; Chen, C.;
Zhai, H.; Hong, H. J . Organomet. Chem. 2000, 613, 68. For some recent
leading references see also: (e) Alt, H. G.; Ko¨ppl, A. Chem. Rev. 2000,
100, 1205. (f) Coates, G. W. Chem. Rev. 2000, 100, 1223. (g) Hlatky,
G. G. Chem. Rev. 2000, 100, 1347. (h) Chen, E.; Marks, T. J . Chem.
Rev. 2000, 100, 1391. (i) Britovsek, V. C. Gibson, G. J . P.; Wass, D. F.
Angew. Chem., Int. Ed. Engl. 1999, 38, 428.
(2) Some references for vanadium chemistry: (a) Reardon, D.;
Conan, F.; Gambarotta, S.; Yap. G.; Wang, Q. J . Am. Chem. Soc. 1999,
121, 9318. (b) Witte, P. T.; Meetsma, A.; Hessen, B. J . Am. Chem. Soc.
1997, 119, 10561. (c) Witte, P. T.; Meetsma, A.; Hessen, B. Organo-
metallics 1999, 18, 2944. (d) Brusee, E. A. C.; Meetsma, A.; Hessen,
B.; Teuben, J . H. Organometallics 1998, 17, 4090. (e) Lorber, C.;
Donnadieu, B.; Choukroun, R. J . Chem. Soc., Dalton Trans. 2000, 4497.
(f) Scheuer, S.; Fischer, J .; Kress, J . Organometallics 1995, 14, 2627.
(g) Calderazzo, F.; Ferri, I.; Pampaloni, G. Organometallics 1999, 18,
2452.
In toluene, the reaction of 1 with B(C6F5)3 gives an
immediate insoluble blue-violet oil with a nearly color-
less supernatant solution. This is a rapid reaction that
precluded observation of intermediates. Nevertheless,
formation of C2H6 is observed by 1H NMR when the
reaction is performed in deuterated toluene or benzene.
An NMR tube containing a weighted amount of 1 (0.05
mmol) and B(C6F5)3 (0.05 mmol) is filled with deuterated
solvent at -80 °C and sealed. After the temperature is
allowed to reach room temperature, the tube is moni-
1
tored by H NMR. The presence of a peak at δ(C6D5-
(3) Choukroun, R.; Moumboko, P.; Chevalier, S.; Etienne, M.;
Donnadieu, B. Angew. Chem., Int. Ed. 1998, 37, 3169.
(4) Choukroun, R.; Douziech, B.; Pan, C.; Dahan, F.; Cassoux, P.
Organometallics 1995, 14, 4471.
(5) J ordan, R. F.; La Pointe, R. E.; Bajgur, C. S.; Echols, S. F.;
Willett, R. J . Am. Chem. Soc. 1987, 109, 4111.
(6) Bochmann, M.; J aggar, A. J .; Wilson, L. M. Polyhedron 1989, 8,
1838.
(7) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1991, 113,
3623.
(9) Choukroun, R.; Lorber, C.; Donnadieu, B.; Henner, B.; Frantz,
R.; Guerin, C. J . Chem. Soc., Chem. Commun. 1999, 1099.
(10) Morris, R. J .; Wilson, S. R.; Girolami, G. S. J . Organomet. Chem.
1994, 480, 1.
(11) Protasiewicz, J . D.; Bianconi, P. A.; Williams, I. D.; Liu, S.; Rao,
C. P.; Lippard, S. J . Inorg. Chem. 1992, 31, 4134.
(12) Hessen, B.; Teuben, J . H.; Lemmen, T. H.; Huffman, J . C.;
Caulton, K. G. Organometallics 1995, 4, 946.
(13) Hessen, B.; Lemmen, T. H.; Luttikhedde, H. J .; Teuben, J . H.;
Petersen, J . L.; Huffman, J . C.; J agner, S.; Caulton, K. G. Organome-
tallics 1987, 6, 2354.
(8) Guzei, I. A.; Stockland, R. A., J r.; J ordan, R. F. Acta Crystallogr.
2000, C56, 635.
10.1021/om010894b CCC: $22.00 © 2002 American Chemical Society
Publication on Web 02/22/2002

Cationic Vanadium(IV) Methyl Complexes
Organometallics, Vol. 21, No. 6, 2002 1125
F igu r e 2. EPR (X-band) of a stoichiometric amount of 1
and B(C6F5)3 in THF: (a) first derivative spectrum; (b) a
part of the second derivative spectrum showing the sup-
erhyperfine coupling of the unpaired electron of the vana-
dium atom with a methyl group.
F igu r e 1. Molecular structure of the cation in 2 showing
the labeling scheme; hydrogen atoms are omitted for
clarity. The structure of the [BPh4]- ion is normal. Selected
bond lengths [Å] and angles [deg]: V-C(3) 2.221(5),
V-N(1) 2.096(4), C(1)-N(1) 1.151(1), V-Cp1 1.950, V-Cp2
1.961, N(1)-V-C(3) 82.67(19), Cp1-V-CP2 136.69, Cp1-
V-C(3) 103.53, Cp1-V-N(1) 107.30, Cp2-V-C(3) 104.74,
Cp2-V-N(1) 108.46 (Cp1 and Cp2 are the centroids of
C(11)-C(15) and C(21)-C(25) rings, respectively).
Sch em e 3
Sch em e 1
slightly soluble 2 in THF develops a less defined EPR
spectrum4 where the hyperfine coupling to the methyl
group could not be observed). The formation of this
species is nearly 90% in the experiments which we
carried out, based on 1 (100%), by comparison with their
EPR spectra, respectively. This complex in THF solution
is unstable and leads to disproportionation and redox
reactions, according to Scheme 3. Complete disappear-
ance of [Cp2VMe(THF)]+ occurs in approximately 2-3
days, whereas the transient Cp2VMe2 EPR signal15
(A(51V) ) 63.4 G) is observed before the formation of an
EPR silent solution. A blue-purple solid was isolated
from this solution and characterized by NMR (see the
Experimental Section) as VIII complex 3. To take into
account the disappearance of the EPR signal of 1, we
suggest that the free borane formed from the redox
reaction (Scheme 3, eq 3) reacted again with 1 formed
from the disproportionation reaction (Scheme 3, eq 2).
Only a major 11B resonance (δ ) 14.7 ppm) was observed
and was identified as [MeB(C6F5)3]-. The derivative
organic byproduct from this cascade of disproportion-
ation-redox reactions, i.e. the presence of ethane,
confirms in part this pathway (the quantification of the
mass balance of the reaction was not undertaken, due
to the various oxidizing reactions of the counteranion
with VIV: the decapentafluorobiphenyl (C6F5)2 was also
identified in the reaction by GC/MS and its presence is
probably due to another mode of redox reaction of the
anion). On the other hand, with B(C6F5)3 in the presence
of acetonitrile, the formation of the adduct complex CH3-
Sch em e 2
CD3) 0.81 (δ(C6D6) 0.79) is in agreement with the values
obtained for free C2H6 in these solvents. We suggest that
the formation of ethane is probably due to a redox reac-
tion between [CH3B(C6F5)3]- and the vanadium VIV spe-
cies, with concomitant formation of the borane B(C6F5)3.
This oil is soluble in THF and gives, after addition of
pentane, a solid characterized as [Cp2V(THF)][MeB-
(C6F5)3] (3). The magnetic moment of 3 is consistent with
a d2 electronic configuration (µeff ) 2.80 µB). The 1H
NMR spectra of 3 in deuterated acetonitrile or acetone
show free THF resonances, which indicate that ligand
exchange occurs between THF and CD3CN or (CD3)2-
CO to give, presumably, [Cp2V(L)][MeB(C6F5)3] (L )
CD3CN, (CD3)2CO) (L ) CD3CN/(CD3)2CO: δ (Cp) )
139.5/141.5 ppm; by comparison δ (Cp) ) 138.7/140.5
ppm for [Cp2V(THF)BPh4] in deuterated acetonitrile
and acetone, respectively).4,14 In THF, 1 and B(C6F5)3
give a well-resolved EPR signal of a quadruplet of octets
due to the interaction of the unpaired electron with 51V
(I ) 7/2) and the three protons of a methyl group (g )
1.991; A(51V) ) 73.2 G; A(1H) ) 5.1 G), and the
formation of [Cp2VMe(THF)][MeB(C6F5)3] is suggested
(Figure 2, Scheme 3, eq 1) (it is worth noting that very
16
CN‚B(C6F5)3 prevents further reaction with 1.
In conclusion, when the reaction is performed in
acetonitrile with the [B(C6H5)4]- counteranion, the
simplest member of the cationic vanadium series was
structurally characterized. The reaction of Cp2VMe2
with the tris(pentafluorophenyl)borane, B(C6F5)3, in
(15) Li, L.; Marks, T. J . Organometallics 1998, 17, 3996.
(16) Razuvaev, G. A.; Latyaeva, N. V.; Vishinskaya, L. I.; Cherkasov,
V. K.; Korneva, S. E.; Spiridonova, N. N. J . Organomet. Chem. 1977,
129, 169.
(14) Fachinetti, G.; Del Nero, S.; Floriani, C. J . Chem. Soc., Dalton
Trans. 1976, 1046.

1126 Organometallics, Vol. 21, No. 6, 2002
Choukroun et al.
Ta ble 1. Cr ysta llogr a p h ic Da ta for 2
toluene or THF gives oily products. In THF, on the basis
of EPR data, we were able to observe the formation of
the intermediate [Cp2VMe]+ species. In this approach,
the redox reaction of the VIV species with the anionic
part [CH3B(C6F5)3]- was slower than in the reaction of
1 with [NHMe2Ph][B(C6H5)4] in THF, which gives
immediate precipitation of [Cp2V(THF)][BPh4] (Scheme
2). Disproportionation and redox reactions (to give Cp2-
VMe2 and VIII species) according to our previous results
do occur and follow a similar sequence of events.
chemical formula
molecular wt
temperature
space group
C37H36BNV
556.42
160(2) K
monoclinic, P21/n
a ) 9.5093(16) Å
b ) 13.5601(15) Å
c ) 22.947(4) Å
â ) 95.78(2)°
cell constants
volume
2944.0(8) Å3
Z, calcd density
abs coeff
4, 1.255 mg/m3
0.363 mm-1
F(000)
1172
no. of reflns collected/unique
refinement method
no. of data/restraints/params
abs corr
19189/4220 [R(int) ) 0.0912]
full-matrix least-squares on F2
4220/0/363
Exp er im en ta l Section
semiempirical24
0.289-0.733
Gen er a l P r oced u r es. All syntheses and subsequent ma-
nipulations were carried out under argon by conventional
Schlenk tube techniques or using a drybox (Vacuum Atmo-
sphere Dry-Lab) filled with argon. Liquids were transferred
via syringe or cannula. All solvents were dried by conventional
methods, distilled under argon, and degassed before use. Cp2-
Tmin - Tmax
goodness-of-fit on F2
final R indices [I>2σ(I)]
R indices (all data)
largest diff peak and hole
1.115
R1 ) 0.0646, wR2 ) 0.1522
R1 ) 0.0895, wR2 ) 0.1676
(0.460 and -0.472) e Å-3
18
VMe217and B(C6F5)3 were prepared according to previously
cally, introduced into the capillary tube, and analyzed by EPR.
The acquisition parameters were kept constant for both the
unknown and the standard sample measurements.
reported procedures. We have reported the preparation of [Cp2-
VMe(CH3CN)][B(C6H5)4] in
a
previous paper.4 Elemental
analyses were performed at the laboratory (C, H) with a CCD-
OMA4 detector and a Notch filter. Magnetic susceptibility
measurements were carried out by Faraday’s method. EPR
spectra were obtained using a BRUKER ESP 300E spectrom-
eter. NMR spectra were recorded at room temperature on
Fourier transform NMR, Bruker AC200 (at 200.133 MHz for
1H, 188.298 MHz for 19F), and AMX400 (128.378 MHz for 11B)
spectrometers.
[Cp2V(THF)][MeB(C6F5)3] (3). A toluene solution of B(C6F5)3
(164 mg, 0.32 mmol) was added to 1 (63 mg, 0.3 mmol)
dissolved in 5 mL of toluene at room temperature, under
stirring. Viscous insoluble blue-violet oil was formed, which
was allowed to settle nearly 1 day without stirring until the
supernatant liquid became nearly colorless. Repeated decanta-
tions of the above liquid followed by toluene washings gave
an oily product, which was solubilized in a small amount of
THF (2-3 mL). Addition of pentane (15 mL) led to a precipi-
tate, which was filtered, washed with pentane and toluene,
and dried under vacuum; yield 70%. 1H NMR (δ in ppm), in
CD3CN: 139.5 (br, ∆ν1/2 ) 1300 Hz, 10H, Cp); 3.60, 1.78 (free
THF in acetonitrile); 0.37 (br, 3H, CH3B(C6F5)3); in THF-d8:
147.0 (br, ∆ν1/2 ) 1300 Hz, 10H, Cp); 3.44, 1.65 (br, 4H,4H; a
single set of broadened THF resonances is observed and shows
that exchange of free and coordinated THF on the paramag-
netic center is rapid); 0.66 (br, 3H, CH3B(C6F5)3). 19F NMR in
THF-d8: -49.77 (o-F); -84.12 (p-F); - 85.12 (m-F). 11B NMR
X-r a y An a lysis of 2. A 10 mL CH3CN solution of 1 (42 mg,
0.199 mmol) and [NHMe2Ph][BPh4] (88 mg, 0.200 mmol) were
mixed at room temperature. After 5 mn stirring, a large
amount of purple solid 2 was filtered rapidly and the filtrate
left for one week at 0 °C, to give suitable crystals of 2.
Data were collected at low temperature, T ) 160 K, on a
IPDS STOE diffractometer using graphite-monochromated Mo
KR radiation (λ ) 0.71073 Å) and equipped with an Oxford
Cryosystems Cryostream cooler device. The final unit cell
parameters were obtained by means of a least-squares refine-
ment performed on a set of 5000 well-measured reflections;
crystal decay was monitored during the data collection, and
no significant fluctuations of intensities were observed. The
structure was solved by direct methods using SIR9219 and
refined by means of least-squares procedures on F2 with the
aid of the program SHELXL9720 included in the software
package WinGX version 1.63.21 The atomic scattering factors
were taken from International Tables for X-Ray Crystal-
lography.22 All hydrogens atoms were located on a difference
Fourier map and refined by using a riding model; consequently
all coordinates of these H atoms have been introduced as fixed
coordinates in the refinement with an isotropic thermal
parameter fixed at 20% higher than those of the carbons atoms
to which they are connected. All non-hydrogens atoms were
anisotropically refined, and in the last cycles of refinement a
weighting scheme was used, where weights are calculated from
the following formula: w ) 1/[σ2(Fo2) + (aP)2 + bP] where P )
in THF-d8 (128.3776 MHz): -14.7. Anal. Calcd for C32H18BF15
OV: C, 50.23; H, 2.37. Found: C, 50.15; H, 2.26.
-
2
(Fo + 2Fc2)/3. Drawing of the molecule is performed with the
program ORTEP3223 with 50% probability displacement el-
lipsoids for non-hydrogen atoms. Crystallographic data of 2
are summarized in Table 1.
Rea ction of Cp 2VMe2 w ith B(C6F 5)3 in THF . A freshly
prepared solution of B(C6F5)3 (102 mg, 0.2 mmol) in THF (5
mL) was added to 1 (42 mg, 0.2 mmol) in 5 mL of THF at room
temperature (an exact amount or a very slight excess of 1 was
necessary to entirely consume the borane to avoid the poly-
merization of THF in the presence of B(C6F5)3). The blue
solution formed was monitored by EPR for 2-3 days until the
complete disappearance of any EPR signal. The solution was
reduced in vacuo to 1/3 of its volume and pentane added to
Su p p or tin g In for m a tion Ava ila ble: Structural diagram
with full atom labeling and tables of bond distances, angles,
anisotropic parameters, and atomic coordinates for 2. This
material is available free of charge via the Internet at
http://pubs.acs.org.
1
give a blue-purple precipitate of 3, characterized by H NMR.
OM010894B
Another unidentified minor species (roughly 10%) was also
1
observed in the H NMR and 11B spectra (δCp ) 126 ppm and
(19) Altomare, A.; Cascarano, G.; Giacovazzo, G.; Guagliardi, A.;
Burla, M. C.; Polidori, G.; Camalli, M. J . Appl. Crystallogr. 1994, 27,
435.
(20) Sheldrick, G. M. SHELX97 [includes SHELXS97, SHELXL97,
CIFTAB]-Programs for Crystal Structure Analysis (Release 97-2);
Institu¨t fu¨r Anorganische Chemie der Universita¨t: Go¨ttingen, Ger-
many, 1998.
(21) Farrugia, L. J . J . Appl. Crystallogr. 1999, 32, 837.
(22) International Tables for X-Ray Crystallography; Kynoch
Press: Birmingham, England, 1974; Vol IV.
(23) Farrugia, L. J . J . Appl. Crystallogr. 1997, 30, 565.
(24) Walker, N.; Stuart, D. Acta Crystallogr. A 1983, 39, 158.
-13.4 ppm, respectively).
EP R Exp er im en ts. A solution of 1 in THF was prepared,
and an aliquot of the solution was introduced into a standard-
ized capillary tube for EPR measurements. This EPR spectrum
served as a standard for the reaction. The solid borane was
then added to the solution, and aliquots were removed periodi-
(17) Foust, D. F.; Rausch, M. D.; Samuel, E. J . Organomet. Chem.
1980, 193, 209.
(18) Massey, A. G.; Park, A. J . J . Organomet. Chem. 1964, 2, 245.