Zwitterionic, Ring-Borylated Vanadium(III) Complexes from [Cp 2VCO] and B(C6F5)3

Article abstract of DOI:10.1021/om034383w

The reaction of the vanadium(II) carbonyl [Cp₂V(CO)] and B(C₆F₅)₃ resulted in formation of zwitterionic, ring-borylated vanadium(III) complexes [(Cp)(C₅H₄B)C ₆F₅)₃V] (3) and [(Cp)(C₅H ₄B(C₆F₅)₃)V(CO)₂] (4) and of the salt [Cp₂V(CO)₂] [HB(C₆F ₅)₃] (5). All were characterized by crystallography. Formation of a hydride vanadium(IV) [(Cp)C₅H₄B(C ₆F₅)₃VH(CO)] obtained by the electrophilic addition of the borane at the Cp-ring followed by redox and disproportionation reaction is suggested to account for these results.

Full text of DOI:10.1021/om034383w

1434
Organometallics 2004, 23, 1434-1437
Zw itter ion ic, Rin g-Bor yla ted Va n a d iu m (III) Com p lexes
fr om [Cp 2VCO] a n d B(C6F 5)3
Robert Choukroun,* Christian Lorber, and Bruno Donnadieu
Laboratoire de Chimie de Coordination, CNRS, 205 Route de Narbonne,
31077 Toulouse Cedex, France
Received December 18, 2003
The reaction of the vanadium(II) carbonyl [Cp2V(CO)] and B(C6F5)3 resulted in formation
of zwitterionic, ring-borylated vanadium(III) complexes [(Cp)(C5H4B(C6F5)3)V] (3) and
[(Cp)(C5H4B(C6F5)3)V(CO)2] (4) and of the salt [Cp2V(CO)2][HB(C6F5)3] (5). All were character-
ized by crystallography. Formation of a hydride vanadium(IV) [(Cp)(C5H4B(C6F5)3)VH(CO)]
obtained by the electrophilic addition of the borane at the Cp-ring followed by redox and
disproportionation reaction is suggested to account for these results.
In tr od u ction
The reactivity of the borane B(C6F5)3 toward organic
and organometallic substrates is of current interest.
New organic reactions, new catalytic processes, and new
reactivity pathways have been observed for this borane.1
In our studies of the reactivity of B(C6F5)3 (1) with
organometallic complexes of the groups 4 and 5 ele-
ments,2,3 in which catalytic application in olefin polym-
erization is well known, we have explored its reactivity
with [Cp2Ti(CO)2]. The product of this reaction was the
acylborane derivative [Cp2Ti(CO)(η2-OCB(C6F5)3].3 The
preferential attack of borane 1 at the carbon atom of a
carbonyl ligand is puzzling if we consider that attack
at the more nucleophilic oxygen atom of the carbonyl
ligand should be favored.4 Thus we decided to extend
our investigation of the reactivity of 1 toward the readily
available [Cp2VCO] (2).
F igu r e 1. Molecular structure of 3, showing 50% prob-
ability thermal ellipsoids and partial atom-labeling schemes.
Selected bond distances (Å) and angles (deg): V(1)‚‚‚F(36)
2.1568(14), C(5a)-B(1) 1.639(3), (Cp)-V(1) 1.923, (CpB)-
V(1) 1.913, (Cp)-V(1)-(CpB) 144.43. (CpB) and (Cp) are the
centroids of C(1a)-C(5a) and C(6a)-C(10a) rings, respec-
tively.
Resu lts a n d Discu ssion
The carbonyl complex [Cp2VCO] (2) reacted with 1
in pentane to give a yellow-brown precipitate that
contained a crystalline air-sensitive blue product. The
latter, formed in low yield, was isolated by careful
separation by hand. This product is a paramagnetic
high-spin VIII complex (µeff ) 2.85 µB). Its structure was
shown by X-ray crystallography to be that of zwitterionic
[(η5-Cp)(η5-C5H4B(C6F5)3)V] (3) (Figure 1). The borane
is linked to one of the cyclopentadienyl rings, and an
ortho-fluorine atom of one perfluoro phenyl group of the
borane is coordinated to the vanadium center with a V‚‚‚
F distance of 2.1568(14) Å, a separation that is in the
same range as those reported in the literature5 for
fluorine atoms that bridge neighboring vanadium atoms
(2.044-2.173 Å). The paramagnetic vanadium center is
51V NMR silent, whereas a 11B NMR resonance at -14.8
ppm confirmed the presence of a tetracoordinated anion
(we assume that the boron atom is not affected by the
proximity of the paramagnetic vanadium center). Elec-
trophilic substitution of a hydrogen atom of the Cp ring
by 1 has been observed previously in group 4.6 In
particular, the interaction of the bis(trimethylsilyl)-
acetylene complex of titanocene [Cp2Ti(Me3SiC2SiMe3)]
with 1 gave a zwitterionic complex of titanium(III),
* Corresponding author. E-mail: choukrou@lcc-toulouse.fr.
(1) (a) Piers, W. E.; Chivers, T. Chem. Soc. Rev. 1997, 26, 345-354.
(b) Stoddard, J . M.; Shea, K. J . Organometallics 2003, 22, 1124-1131.
(c) Parks, D. J .; Piers, W. E.; Parvez, M.; Atencion, R.; Zaworotko, M.
J . Organometallics 1998, 17, 1369-1377. (d) Parks, D. J .; Blackwell,
J . M.; Piers, W. E. J . Org. Chem. 2000, 65, 3090-3098. (e) Mountford,
A. J .; Hughes, D. L.; Lancaster, S. Chem. Commun. 2003, 2148-2149.
(f) Watson, I. D.; Yudinn, A. J . Org. Chem. 2003, 68, 5160-5167. (g)
Chen, E. Y.-X.; Marks, T. J . Chem. Rev. 2000, 100, 1391. (h) Bochmann,
M. J . Chem. Soc., Dalton Trans. 1996, 225. (i) Britovsek, G. J . P.;
Gibson, V. C.; Wass, D. F. Angew. Chem., Int. Ed. 1999, 38, 428.
(2) Wolff, F.; Choukroun, R.; Lorber, C.; Lepetit, C.; Donnadieu, B.
Eur. J . Inorg. Chem. 2003, 628-632.
(5) (a) Fairhurst, S. A.; Hughes, D. L.; Leigh, G. J .; Snaders, J . R.;
Weisner, J . J . Chem. Soc., Dalton Trans. 1994, 2591-2598. (b)
Bukovec, P.; Milicev, S.; Demsar, A.; Golic, L. J . Chem. Soc., Dalton
Trans. 1981, 1802-1806. (c) Buchholz, N.; Leimku¨hler, M.; Kiriazis,
L.; Mattes, R. Inorg. Chem. 1988, 27, 2035-2039.
(3) Choukroun, R.; Lorber, C.; Lepetit, C.; Donnadieu, B. Organo-
metallics 2003, 22, 1995-1997.
(4) Braunschweig, H.; Klinkhammer, K. W.; Koster, M.; Radacki,
K. Chem. Eur. J . 2003, 9, 1030-1309.
10.1021/om034383w CCC: $27.50 © 2004 American Chemical Society
Publication on Web 02/17/2004

Zwitterionic, Ring-Borylated V(III) Complexes
Organometallics, Vol. 23, No. 6, 2004 1435
F igu r e 3. Molecular structure of 5, showing 50% prob-
ability thermal ellipsoids and partial atom-labeling schemes.
Selected bond distances (Å) and angles (deg): V(C1) 1.965-
(3), V-C(2) 1.964(2), C(1)-O(1) 1.132(3), C(2)-O(2) 1.135-
(3), (Cp)-V (or (Cp′)-V) 1.901, (Cp)-V-(Cp′) 138.01,
B-H(1B) 1.14(2), C(1)-V-C(2) 86.63(11). (Cp) and (Cp′)
are the centroids of C(11)-C(15) and C(21)-C(25) rings,
respectively.
F igu r e 2. Molecular structure of 4, showing 50% prob-
ability thermal ellipsoids and partial atom-labeling schemes.
Selected bond distances (Å) and angles (deg): V(C1) 1.9484-
(17), V-C(2) 1.9686(17), C(1)-O(1) 1.1369(19), C(2)-O(2)
1.133(2), B-C(21) 1.655(2), C(1)-V-C(2) 85.44(7), (Cp)-
V(1) 1.930, (CpB)-V(1) 1.924, (Cp)-V(1)-(CpB) 139.15.
(CpB) and (Cp) are the centroids of C(21)-C(25) and C(11)-
C(15) rings, respectively.
ratio, as judged by 1H NMR (0-5%), and isolated 5 often
was contaminated by small amounts of 4. In another
procedure, the synthesis carried out in a small amount
of toluene as solvent gave 5 as an immediate orange
crystalline product in high yield. The filtrate, after 2-3
days at low temperature (-30 °C), afforded blue crystals
of 3. After filtration, the filtrate was layered with
pentane to give a brown precipitate, which was analyzed
[(η5-Cp)(η5-C5H4B(C6F5)3)Ti], in which ortho-fluorine
atoms of two C6F5 groups are coordinated to the
titanium center in a pseudotetrahedral geometry.6b The
difference in the reactivity between the titanocene and
vanadocene units could be the result of a steric effect:
the larger atomic radius of Ti versus V may allow two
fluorine atoms to coordinate at the Ti center.
1
by H NMR as 4 contaminated with 5. Both complexes
Two other products were contained in the yellow-
4 and 5 are diamagnetic (confirmed by Faraday balance
experiments and multinuclear NMR). The 11B NMR
shift of 4 (-14.9 ppm) is in the same range as that of 3,
as expected for a tetracoordination of the boron atom.
The resonance of the 11B NMR spectrum of 5 shows a
doublet at -25.5 ppm (1J B-H ) 89 Hz), in agreement
with the presence of the [HB(C6F5)3]- anion,8 which is
1
brown crude precipitate as observed by H NMR spec-
troscopy (the characteristic cyclopentadienyl signals) as
well as by the 51V and 11B NMR spectra, in which two
resonances were observed, respectively. A magnetic
measurement made on the crude product (after careful
and tedious separation of 3) indicated that it consisted
of diamagnetic species. We were able to isolate sepa-
rately each complex by dissolving the crude product in
a small amount of toluene or THF followed by pentane
diffusion. Formation of crystalline, air-sensitive com-
plexes suitable for an X-ray structure determination
were obtained from these selective crystallizations. In
the crystals obtained from THF/pentane solution, a
dicarbonylvanadium(III) species in which the borane is
linked to one of the cyclopentadienyl rings of the
vanadocene unit in the zwitterionic [(η5-Cp)(η5-C5H4B-
(C6F5)3)V(CO)2] (4) (Figure 2) was shown to be present.
Crystals were obtained from toluene/pentane solution,
and the X-ray structure determination established the
formation of a salt, [Cp2V(CO)2][HB(C6F5)3] (5) (Figure
3).7 The isolated 4 often was contaminated by 5 in low
1
also supported by the H NMR spectrum, which shows
1
a quadruplet at 3.63 ppm with J BH ) 91 Hz. The 51V
NMR spectra of 4 and 5 show very low field peaks at
-1652 and 1662 ppm, respectively, due to the high
basicity of the cationic [V]+ moiety.9 Both compounds
have two infrared C-O strechting vibrations (Nujol
mull) at 2050 and 2004 cm-1 and 2038 and 1990 cm-1
for 4 and 5, respectively (to be compared with the bands
at 2050 and 2010 cm-1 reported for the [Cp2V(CO)2]+
cation10).
From these different results, we can draw a scheme
showing the possible formation of 3, 4, and 5. All these
compounds seem to arise from the same parent mol-
(7) Compound 5 is related to the carbonyl salt [Cp2V(CO)2][BPh4],
whose structure has been reported with a disorder that prevents the
accurate location of the atom involved. Atwood, J . L.; Rogers, R. D.;
Hunter, W. E.; Floriani, C.; Fachinetti, G.; Chiesi-Villa, A. Inorg. Chem.
1980, 19, 3812-3817.
(6) (a) Ruwwe, J .; Erker, G.; Fro¨lich, R. Angew. Chem., Int. Ed. Engl.
1996, 35, 80-82. (b) Burlakow, V. V.; Troyanov, S. I.; Letov, A. V.;
Strunkina, L. I.; Minacheva, M. Kh.; Furin, G. G.; Rosenthal, U.; Shur,
V. B. J . Organomet. Chem. 2000, 598, 243-247. (c) Burlakow, V. V.;
Pellny, P.-M.; Arndt, P.; Baumann, W.; Spannenberg, A.; Shur, V. B.;
Rosenthal, U. Chem. Commun. 2000, 241-242. (d) Burlakow, V. V.;
Arndt, P.; Baumann, W.; Spannenberg, A.; Rosenthal, U.; Letov, A.
V.; Lyssenko, K. A.; Korlyukov, A. A.; Strunkina, L. I.; Minacheva, M.
Kh.; Shur, V. B. Organometallics 2001, 20, 4072-4079.
(8) Temme, B.; Erker, G. J . Organomet Chem. 1995, 488, 177-182.
(9) (a) Devore, D. D.; Lichtenhan, J . D.; Takusagawa, E.; Maatta,
A. J . Am. Chem. Soc. 1987, 109, 7408-7416. (b) Rehder, D. Coord.
Chem. Rev. 1991, 110, 161-210. (c) Priebsch, W.; Rehder, D. Inorg.
Chem. 1985, 24, 3058-3062.
(10) Calderazzo, F.; Bacciarelli, S. Inorg. Chem. 1963, 2, 721-723.

1436 Organometallics, Vol. 23, No. 6, 2004
Choukroun et al.
Ta ble 1. Su m m a r y of Cr ysta l Da ta , Da ta Collection , a n d Str u ctu r e Refin em en t P a r a m eter s for 3-5
3
4
5
fw
1384.20
180
0.71073
monoclinic
P21/c
17.010(5)
15.787 (5)
18.810(5)
94.282 (5)
5037(3)
4, 1.825
2720
748.12
180
0.71073
monoclinic
P21/c
10.819(5)
13.785(5)
18.532(5)
105.417(5)
2668.7(17)
4, 1.862
750.14
160
0.71073
monoclinic
P21/n
14.594(5)
16.127(5)
11.890(5)
97.046(5)
2777.3(17)
4, 1.794
temperature (K)
wavelength (Å)
cryst syst
space group
a (Å)
b (Å)
c (Å)
â (deg)
V (Å3)
Z, density (g cm-3
F(000)
)
1472
0.509
1480
0.489
abs coeff (mm-1
)
0.525
2θ range (deg)
3.3 6-31.79
46 805/15892
(Rint ) 0.0483)
63.58 (92.5)
15 892/0/811
0.926
2.91-30.51
54 611/7749
(Rint ) 0.0369)
61.02 (95.1)
7749/0/442
1.099
2.44-28.13
26 433/6555
(Rint ) 0.0492)
79.8
6555/0/446
1.015
no. of reflns collected/unique
completeness to 2θ (%)
no. of data/restraints/params
GOF on F2
final R indices (I>2σ(I))
R1 ) 0.0483,
wR2 ) 0.1094
R1 ) 0.0936,
wR2 ) 0.1269
0.370 and - 0.456
R1 ) 0.0369,
wR2 ) 0.0951
R1 ) 0.0469,
wR2 ) 0.1001
0.326 and -0.355
R1 ) 0.0369,
wR2 ) 0.0799
R1 ) 0.0663,
wR2 ) 0.0911
0.266 and -0.249
R indices (total)
largest diff peak and hole (e‚Å-3
)
Sch em e 1
ecule. Electrophilic addition of 1 at the Cp-ring occurred
and afforded the suggested intermediate vanadium(IV)
hydride [(η5-Cp)(η5-C5H4B(C6F5)3)VH(CO)].11 The reduc-
tive elimination of the hydride leads to simultaneous
formation of 0.5 equiv of the monocarbonylvanadium-
(III) [(Cp)(C5H4B(C6F5)3)V(CO)] {A} and 0.5 equiv of the
monocarbonyl cationic [Cp2V(CO)]+ species associated
with the anion [HB(C6F5)3]- {B}. Disproportionation of
{A} gives the borane-substituted cyclopentadienyl com-
plexes 3 and 4, whereas {B} disproportionates to 5 and
a suggested [Cp2VH][HB(C6F5)3] species that we have
not been able to observe due to its probable decomposi-
tion (Scheme 1). Gas phase analysis by MS of the gas
above the reaction mixture, in a closed vessel, did not
show evidence of H2 evolution during the synthesis of
the crude product in pentane.
Con clu sion
In summary, combination of 1 with [Cp2VCO] gives
new vanadium complexes. In the same reaction, three
vanadium complexes were found showing the complex-
ity of the vanadium chemistry, resulting from the
oxidation of the metal center toward the divalent
vanadocene 2. Complexes 3 and 4 represent the first
structurally characterized ring-borylated vanadium zwit-
terionic complexes.
and stored in a drybox over activated 4 Å molecular sieves.
Deuterated solvents were degassed and dried over activated
4 Å molecular sieves. NMR data were recorded using Bruker
AMX-400 and AC-200 spectrometers, referenced internally to
residual protio solvent (1H) resonances, and are reported
relative to tetramethylsilane (δ ) 0 ppm). 19F NMR (188.298
MHz) spectra were recorded on a Bruker AC-200 spectrometer
(reference CF3CO2H). 51V NMR (105.24 MHz; reference VOCl3
in C6D6, 9:1) and 11B NMR (128.37 MHz; reference BF3‚Et2O)
spectra were recorded on a Bruker AMX-400 spectrometer.
Elemental analyses (C, H) were performed at the Laboratoire
de Chimie de Coordination (Toulouse, France). [Cp2VCO] and
B(C6F5)3 were prepared according to the literature.12,13
Exp er im en ta l Section
All manipulations were carried out using standard Schlenk
line or drybox techniques under an atmosphere of argon.
Solvents were refluxed and dried over appropriate drying
agents under an atmosphere of argon, collected by distillation,
P r ep a r a tion of [(η5-Cp )(η5-C5H4B(C6F 5)3)V] (3), [(η5-Cp )-
(η5-C5H4B(C6F 5)3)V(CO)2] (4), a n d [Cp 2V(CO)2][HB(C6F 5)3]
(5). To a stirred pentane solution (5 mL) of [Cp2VCO] (2) (36
mg, 0.2 mmol) was added in small portions solid B(C6F5)3 (102
mg, 0.2 mmol). The resulting yellow-brown slurry was left one
week at room temperature until blue crystals of 3 appeared.
After careful hand-separation of 3, the yellow-brown solid was
dissolved in THF (1-2 mL) and layered with pentane to give
(11) V-H bonds were reported in the literature: (a) J onas, K.;
Wiskamp, V. J . Am. Chem. Soc. 1983, 105, 5480-5481. (b) Bansemer,
J . R. L.; Huffman, C.; Caulton, K. G. J . Am. Chem. Soc. 1983, 105,
6163-6164. (c) Berno, P.; Gambarotta, S. Angew. Chem. 1995, 107,
871-873; Angew. Chem., Int. Ed. Engl. 1995, 34, 822-824. (d) Clancy,
G. P.; Clark, H. C. S.; Clentsmith, G. K. B.; Cloke, F. G. N.; Hitchcock,
P. B. J . Chem. Soc., Dalton Trans. 1999, 3345-3347. Very recently,
the zwitterionic hydride ring-borylated ansa-chromocene [Me4C2(η5-
C5H4)(η5-C5H3B(C6F5)3)CrH(CO)] has been isolated from [Me4C2(η5-
C5H4)2Cr(CO)] and [H(OEt2)2B(C6F5)4]. Sinnema, P.-J .; Shapiro, P. J .;
Foo, D. M. J .; Twamley, B. J . Am. Chem. Soc. 2002, 124, 10996-10997.
(12) Massey, A. G.; Park, A. J . J . Organomet. Chem. 1966, 5, 218.
(13) Calderazzo, F.; Fachinetti, G.; Floriani, C. J . Am. Chem. Soc.
1974, 96, 3695-3696.

Zwitterionic, Ring-Borylated V(III) Complexes
Organometallics, Vol. 23, No. 6, 2004 1437
4 as a crystalline, orange solid suitable for X-ray structure
determination. In another experiment (using the same experi-
mental conditions), the crude yellow-brown product was dis-
solved in toluene (1 mL) and layered with pentane to give 5
as a crystalline, orange-yellow solid suitable for X-ray structure
determination. Note that 4 is very often contaminated by some
proportion of 5 and similarly 5 by some amount of 4, as
indicated by 1H NMR spectroscopy. C, H analytical results are
A semiempirical correction absorption14 was applied to the
data. The structure was solved by direct methods using
SIR9215 and refined by least-squares procedures on F2 with
the aid of SHELXL97,16 included in WinGX (version 1.63).17
The atomic scattering factors were taken from International
Tables for X-Ray Crystallography.18 All hydrogen atoms were
located on a difference Fourier map. All the remaining non-
hydrogen atoms were anisotropically refined, and in the last
refinement cycles a weighting scheme was used where weights
were calculated from the following formula: w ) 1/[σ2(Fo2) +
in the same range for 4 (C30H9BF15O2V) as for 5 (C30H11
-
BF15O2V) and fall within the experimental error for both
compounds, and they are not indicative of the purity of the
product. Analysis of 4 and 5 was attempted for characteriza-
tion and gave reproducible analysis. In another procedure, the
crude yellow product can be obtained directly by admission of
CO gas in a stoichiometric mixture of [VCp2] and 1 in pentane.
3: µeff ) 2.85 µB. Anal. Calcd for C28H9BF15V: C 48.59, H
1.31. Found: C 48.40, H 1.22. Yield: 22 mg (50%). 4: 1H NMR
(200 MHz, CD3CN) 5.19 (5H, Cp), 5.36 (b, 2H, C5H4) 5.49 (t,
2H, C5H4); 19F NMR (CD3CN) -52.9; -86.2; -91.0 (o, p, m-F,
C6F5); 11B (CD3CN) -14.9; 51V (CD3CN) -1652; IR (Nujol mull)
2
(aP)2 + bP], where P ) (Fo2 + 2Fc )/3. Drawing of the molecules
was performed using the program ORTEP32.19 Criteria for a
satisfactory, complete analysis were the ratio of rms shift to
standard deviation being less than 0.1 and no significant
features in final difference maps.
Ack n ow led gm en t. We thank the CNRS for finan-
cial support.
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data for compounds 3, 4, and 5 including ORTEP diagrams
and tables of crystal data and data collection parameters,
atomic coordinates, anisotropic displacement parameters, and
all bond lengths and bond angles. This material is available
free of charge via the Internet at http://pubs.acs.org.
ν
CO 2050, 2004. Anal. Calcd for C30H9BF15O2V: C 48.16, H 1.21.
1
Found: C 48.4, H 1.35. Yield: 21 mg (59%). 5: H NMR (200
MHz, CD3CN) 5. 59 (10H, Cp), 3.63 (q (1J (BH) ) 91 Hz), B-H);
19F (CD3CN) -58.9, -88.8, -92.0 (o, p, m-F, C6F5); 11B (CD3-
CN) -25.5 (d, (1J (BH) ) 87 Hz), B-H); 51V: -1661; IR (Nujol
mull) ν(CO) 2038, 1990; ν(BH) 3123. Anal. Calcd for C30H11
-
BF15O2V: C 48.03, H 1.48. Found: 48. 38, C 1.30. Yield: 30
mg (83%).
OM034383W
Cr ysta llogr a p h ic Da ta for 3, 4, a n d 5. Selected crystals,
sensitive to air and moisture, were suspended in oil on a glass
slide. Under a microscope, a single block was isolated. For
structures 3, 4, and 5 (Table 1), data were collected using a
Stoe Imaging Plate Diffraction System (IPDS). The final unit
cell parameters were obtained by least-squares refinement of
a set of 5000 reflections, and crystal decay was monitored by
measuring 200 reflections by image. No fluctuations of the
intensity were observed over the course of the data collection.
(14) Walker, N.; Stuart, D. Acta Crystallogr., Sect. A 1983, 39, 158.
(15) Altomare, A.; Cascarano, G.; Giacovazzo, G.; Guagliardi, A.;
Burla, M. C.; Polidori, G.; Camalli, M. J . Appl. Crystallogr. 1994, 27,
435.
(16) Sheldrick, G. M. SHELX97, Program for Crystal Structure
Analysis; University of Go¨ttingen: Germany, 1998.
(17) Farrugia, L. J . J . Appl. Crystallogr. 1999, 32, 837.
(18) International Tables for X-Ray Crystallography; Ibers, J . A.,
Hamilton, W. C., Eds.; Kynoch Press: Birmingham, England, 1974;
Vol. IV.
(19) Farrugia, L. J . J . Appl. Crystallogr. 1997, 30, 565.