Oxidation products of vanadocene and of its permethylated analogue, including the isolation and the reactivity of the unsolvated [VCp2]+ cation

Article abstract of DOI:10.1021/om9809320

The one-electron oxidation of vanadocene, VCp₂, by [FeCp₂]⁺ in toluene affords the 14-electron [VCp₂]⁺ cation, which has been isolated as an unsolvated species for the first time. Vanadium hexacarbonyl reacts with VCp₂ to give the μ-isocarbonyl derivative Cp₂V(μ-OC)V-(CO)₅ as a transient species, which has been characterized in solution by IR analysis. By reaction of VCp₂ with V(¹³CO)₆ followed by treatment with ¹²CO, the ionic dicarbonyl derivative [VCp₂(¹²CO)₂][V(¹³CO)₆] is formed, thus showing that during the formation of the ionic compound no redistribution of the carbonyl ligands between the two metal centers occurs. Bis(cyclopentadienyl)vanadium(II) and Co₂(CO)₈ give Cp₂VCo(CO)₄, which slowly decomposes in solution even at low temperature to give [VCp₂(CO)₂][Co(CO)₄], which was identified by conventional methods, including single-crystal X-ray diffraction. The reactivity of the unsolvated [VCp₂]⁺ cation as well as that of the heterobimetallic compound containing vanadium and cobalt with several Lewis bases is reported.

Full text of DOI:10.1021/om9809320

2452
Organometallics 1999, 18, 2452-2458
Oxid a tion P r od u cts of Va n a d ocen e a n d of Its
P er m eth yla ted An a logu e, In clu d in g th e Isola tion a n d th e
Rea ctivity of th e Un solva ted [VCp 2]+ Ca tion
Fausto Calderazzo, Isabella Ferri,† and Guido Pampaloni*
Dipartimento di Chimica e Chimica Industriale, Universita` di Pisa, Via Risorgimento 35,
I-56126 Pisa, Italy
Ulli Englert
Institut fu¨r Anorganische Chemie der Rheinisch-Westfa¨lischen Technischen Hochschule,
Professor Pirlet-Strasse 1, D-52074 Aachen, Germany
Received November 16, 1998
The one-electron oxidation of vanadocene, VCp2, by [FeCp2]+ in toluene affords the 14-
electron [VCp2]+ cation, which has been isolated as an unsolvated species for the first time.
Vanadium hexacarbonyl reacts with VCp2 to give the µ-isocarbonyl derivative Cp2V(µ-OC)V-
(CO)5 as a transient species, which has been characterized in solution by IR analysis. By
reaction of VCp2 with V(13CO)6 followed by treatment with 12CO, the ionic dicarbonyl
derivative [VCp2(12CO)2][V(13CO)6] is formed, thus showing that during the formation of the
ionic compound no redistribution of the carbonyl ligands between the two metal centers
occurs. Bis(cyclopentadienyl)vanadium(II) and Co2(CO)8 give Cp2VCo(CO)4, which slowly
decomposes in solution even at low temperature to give [VCp2(CO)2][Co(CO)4], which was
identified by conventional methods, including single-crystal X-ray diffraction. The reactivity
of the unsolvated [VCp2]+ cation as well as that of the heterobimetallic compound containing
vanadium and cobalt with several Lewis bases is reported.
In tr od u ction
with Lewis bases L. For example, adducts with CO,6
isocyanides,6a,b tertiary phosphines,6g7 nitriles,8 THF,7
and acetone6g,9 have been obtained from bis(cyclopen-
tadienyl)vanadium(III) halides or by direct oxidation
of vanadocenes in the presence of the appropriate
ligand. Moreover, some authors have reported the
reaction of VCp2 or substituted congeners with metal
carbonyls,6f,10-12 showing that, in some cases, hetero-
bimetallic compounds can be obtained. In the case of
In contrast to the well-developed chemistry of cationic
bis(cyclopentadienyl) derivatives of group 4 elements,
bis(cyclopentadienyl) complexes of vanadium have at-
tracted much less attention, despite their potential
applications in many fields such as bioinorganic chem-
istry,1 Ziegler-Natta catalysis,2 and material chemis-
try.3 As a matter of fact, although the aqueous solutions
of the [VCp2]+ cation were obtained by Wilkinson and
Birmingham more than 40 years ago by reduction of bis-
(cyclopentadienyl)vanadium(IV) perchlorate with the
J ones reagent in acidic aqueous solution,4 a rather
limited number of paper have appeared on the subject.5
(4) Wilkinson, G.; Birmingham, J . M. J . Am. Chem. Soc. 1954, 76,
4281.
(5) Connelly, N. G. Vanadium. In Comprehensive Organometallic
Chemistry; Wilkinson, G., Abel, E. W., Stone, F. G. A., Eds.; Pergamon
Press: Oxford, U.K., 1982; Vol. 4, p 647. Berno, P.; Gambarotta, S.;
Richeson, D. Vanadium. In Comprehensive Organometallic Chemistry;
Wilkinson, G., Abel, E. W., Stone, F. G. A., Eds.; Pergamon Press:
Oxford, U.K., 1995; Vol. 4, p 1.
Due to the electron count of 14, the [VCp2]+ cation
gives adducts of general formula [VCp2Ln]+ by reaction
(6) (a) Gambarotta, S.; Floriani, C.; Chiesi-Villa, A.; Guastini, C.
Inorg. Chem. 1984, 23, 1739. (b) Fachinetti, G.; Del Nero, S.; Floriani,
C. J . Chem. Soc., Dalton Trans. 1976, 203. (c) Connelly, N. G.; Davies,
J . D. J . Organomet. Chem. 1972, 38, 385. (d) Bocarsly, J . R.; Floriani,
C.; Chiesi-Villa, A.; Guastini, C. Inorg. Chem. 1987, 26, 1871. (e) Miller,
G. A.; Therein, M. J .; Trogler, W. C. J . Organomet. Chem. 1990, 383,
271. (f) Calderazzo, F.; Bacciarelli, S. Inorg. Chem. 1963, 2, 721. (g)
Fachinetti, G.; Del Nero, S.; Floriani, C. J . Chem. Soc., Dalton Trans.
1976, 1046. (h) Atwood, J . L.; Rogers, R. D.; Hunter, W. E.; Floriani,
C.; Fachinetti, G.; Chiesi-Villa, A. Inorg. Chem. 1980, 19, 3812.
(7) Choukroun, R.; Douziech, B.; Pan, C.; Dahan, F.; Cassoux, P.
Organometallics 1995, 14, 4471.
(8) Robbins, J . L.; Edelstein, N.; Spencer, B.; Smart, J . C. J . Am.
Chem. Soc. 1982, 104, 1882.
(9) Gambarotta, S.; Pasquali, M.; Floriani, C.; Chiesi-Villa, A.;
Guastini, C. Inorg. Chem. 1981, 20, 1173.
(10) Martin, J .; Mo¨ıse, C. J . Organomet. Chem. 1982, 232, C55.
(11) Martin, J .; Fauconet, M.; Mo¨ıse, C. J . Organomet. Chem. 1989,
371, 87.
(12) Osborne, J . H.; Rheingold, A. L.; Trogler, W. C. J . Am. Chem.
Soc. 1985, 107, 6292.
* To whom correspondence should be addressed.
‡ Present address: CRYOVAC SpA, Via Trento 7, I-20017 Passirana
di Rho, Milano, Italy.
(1) Ko¨pf-Maier, P.; Ko¨pf, H. Chem. Rev. 1987, 87, 1137 and refer-
ences therein.
(2) Spitz, R.; Pasquet, V.; Patin, M.; Guyot, A. The Activation of
Supported Vanadium Catalysts in Ethylene Polymerization. In Ziegler
Catalysts; Fink, G., Mu¨hlhaupt, R., Brintzinger, H. H., Eds.; Springer-
Verlag: Berlin, 1995; p 401. Doi, Y.; Tokuhiro, N.; Nunomura, M.;
Miyake, H.; Suzuki, S.; Soga, K. Living Polymerization of Olefins with
Highly Active Vanadium Catalysts. In Transition Metals and Orga-
nometallics as Catalysts for Olefin Polymerization; Kaminsky, W., Sinn,
H., Eds.; Springer-Verlag: Berlin-Heidelberg, 1988; p 379. Evens, G.
G.; Pijpers, E. M. J .; Seevens, R. H. M. Enhancement of the Activity
of a Vanadium Catalyst for Ethylene Propylene Copolymerization. In
Transition Metal Catalyzed Polymerizations; Quirk, R. P., Ed.; Cam-
bridge University Press: Cambridge, U.K., 1988; p 782.
(3) Miller, J . S.; Epstein, A. J .; Reiff, W. A. Chem. Rev. 1988, 88,
201 and references therein.
10.1021/om9809320 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 06/03/1999

Oxidation Products of Vanadocene
Organometallics, Vol. 18, No. 13, 1999 2453
Rea ction of VCp 2 w ith V(13CO)6 a n d Tr ea tm en t of th e
the reaction of VCp2 with V(CO)6 under a nitrogen
atmosphere “a mixture of at least two different com-
pounds was formed”, but the individual components
could not be resolved.6f
It was therefore of interest to examine in some detail
the possibility of isolating and characterizing the still
elusive, unsolvated, ligand-free [VCp2]+ cation. This
paper shows that this cation can be isolated as the
tetraphenylborate derivative. Attempts to isolate it in
combination with carbonylate anions failed, due to the
easy transformation of the unsolvated cation into the
dicarbonyl compound [VCp2(CO)2]+ by partial decom-
position of the carbonylmetalate anion.
P r od u ct w ith CO. Vanadocene, VCp2 (0.05 g, 0.28 mmol),
was added to a solution of V(13CO)6 (0.06 g, 0.27 mmol) in
19
toluene (5 mL). The IR spectrum of the solution recorded
immediately after the reagents were mixed showed absorptions
at 1995 m, 1924 w-m, 1855 vs, 1818 m-w, 1811 s, and 1613 m
cm-1. Treatment of the solution with CO at atmospheric
pressure caused the formation of an orange solid and decol-
oration. The solvent was removed via cannula, and the solid
was dried in vacuo and identified as [VCp2(CO)2][V(13CO)6]
from its IR spectrum in THF solution (2046 m, 1999 m, 1818
vs cm-1).
Rea ction of VCp 2Cl w ith Na [V(CO)6]. The hexacarbon-
ylvanadate(-I) compound Na[V(CO)6] (0.30 g, 1.24 mmol) was
added to a solution of VCp2Cl (0.27 g, 1.25 mmol) in toluene
(25 mL). The color of the solution changed rapidly from blue
to dark red, and NaCl precipitated. The IR spectrum of the
solution showed absorptions at 2042 m, 1969 w-m, 1897 vs,
1865 s, 1849 m-s, and 1652 m-s cm-1. After 17 h the intensities
of the absorptions at 2042 m, 1969 w-m, 1897 vs, 1865 s, and
1652 m-s cm-1 were reduced with respect to the band at 1849
cm-1. A brown solid with absorptions at 2047 m, 1997 m, and
1851vs cm-1 (THF) was present.
Exp er im en ta l Section
All operations were carried out using standard Schlenk-tube
techniques, under an atmosphere of prepurified argon. The
reaction vessels were oven-dried prior to use. Solvents were
dried by conventional methods.
Elemental analyses were performed with a Carlo Erba
Model 1106 elemental analyzer at the Istituto di Chimica
Farmaceutica of the Facolta` di Farmacia or at the Diparti-
mento di Chimica e Chimica Industriale of the Universita` di
Pisa. Infrared spectra were recorded with a Perkin-Elmer
Model FT 1725X instrument on solutions or Nujol and poly-
(chlorotrifluoroethylene) mulls of the compounds prepared
under rigorous exclusion of moisture and oxygen.
Ph3SnCl (Fluka) and Co2(CO)8 (Fluka) were commercially
available and were used without further purification. The
compounds but-2-yne (Aldrich) and hexafluorobut-2-yne (Al-
drich) were degassed and stored at low temperature under
argon. CF3COOH (Aldrich) was stored in the presence of 15%
(v/v) (CF3CO)2O.
The following reagents were prepared according to the
literature: [PPN]Cl (PPN ) bis(triphenylphosphine)nitrogen-
(1+) cation),13 [FeCp2]BR4 (R ) Ph, 4-C6H4F, 3,5-C6H3(CF3)2)14
VCp2,15 VCp*2,6a VCp2Cl,16 CoCp2,15 Na[Co(CO)4],17 Cp2VCo-
(CO)4,10 V(CO)6,18 nBu4N[V(CO)6],19 Mn2(CO)10,20 and Na[Mn-
(CO)5].21
Rea ction of VCp 2 w ith V(CO)6. VCp2 (0.08 g, 0.44 mmol)
was added to a solution of V(CO)6 (0.08 g, 0.36 mmol) in
toluene (10 mL). The IR spectrum of the solution recorded
immediately after the reagents were mixed showed absorptions
at 2040 m, 1970 w-m, 1896 vs, 1864 s, 1849 s, and 1652 m-s
cm-1. After 24 h the spectrum showed the absorption at 1850
s cm-1 to be the strongest one in the carbonyl stretching region.
Two weak additional bands were observed at 2051 and 2013
cm-1, and a solid was present within the reaction mixture. The
suspension was then filtered, and the dark brown solid thus
obtained was dried in vacuo (0.08 g). The solid had absorptions
(Nujol mull) at 2051 m, 2010 m, and 1840 vs cm-1 typical of
[VCp2(CO)2][V(CO)6].6f
Syn th esis of [VCp 2]BR4 (R ) P h , 4-C6H4F ). Only the
synthesis of [VCp2]BPh4 is described in detail. VCp2 (0.31 g,
1.71 mmol) was added to a suspension of [FeCp2]BPh4 (0.76
g, 1.50 mmol) in toluene (20 mL). An immediate reaction took
place with formation of a green-gray solid in a red-orange
solution. The solid was recovered by filtration, washed with
toluene (2 × 5 mL) and heptane (2 × 5 mL), and dried in vacuo
(0.57 g, 76% yield). IR (Nujol mull): 3087 vw, 3055 m, 1612
vw, 1581 w, 1562 vw, 1427 m, 1266 w-m, 1022 m, 825 s, 737
vs, 612 m-s cm-1. The solid was found to absorb CO in toluene
at 20 °C up to a CO/V molar ratio of 2.0 to give [VCp2(CO)2]-
BPh4, characterized by its IR spectrum in THF solution (IR
(THF): 2047 s, 1999 s cm-1).6f
Data for [VCp2][B(4-C6H4F)4] are as follows. Yield: 72%. IR
(Nujol mull): 1580 m-s, 1488 s, 1257 w, 1209 s, 1157 s, 1015
m, 814 vs, 732 m, 553 s cm-1. The solid was found to absorb
CO in toluene at 20 °C up to a CO/V molar ratio of 1.9 to give
[VCp2(CO)2][B(4-C6H4F)4], characterized by its IR spectrum in
THF solution (IR (THF): 2047 s, 2000 s cm-1).
Rea ction s of [VCp 2]BP h 4. (a ) [P P N]Cl. A suspension of
[VCp2]BPh4 (0.25 g, 0.5 mmol) in toluene (25 mL) was treated
with [PPN]Cl (0.29 g; 0.5 mmol). Immediate reaction with
formation of a green-brown suspension was observed. The
suspension was filtered, and the solid (0.39 g, 91% yield) was
identified as [PPN]BPh4 (IR spectrum in Nujol). The volume
of the solution was reduced to 10 mL, and heptane (20 mL)
was added, which caused the separation of VCp2Cl16 (0.09 g,
83% yield), identified by IR and analytical techniques.
(b) CoCp 2. A solution of CoCp2 (0.305 g, 1.6 mmol) in
toluene (25 mL) was treated with solid [VCp2]BPh4 (0.81 g,
1.62 mmmol). Formation of a deep yellow solid was observed
upon mixing the reagents. The solid was filtered and identified
as [CoCp2]BPh4 (IR). The solution was dried in vacuo, and the
residue was sublimed at ca. 80 °C/10-2 mmHg, affording 0.10
g (91% yield) of VCp2.
(13) Ruff, J . K.; Schlientz, W. J . Inorg. Synth. 1974, 15, 84.
(14) Calderazzo, F.; Pampaloni, G.; Rocchi, L.; Englert, U. Organo-
metallics 1994, 13, 2592.
(15) Zybill, C. E. Complexes with Cyclic Ligands CnHn. In Synthetic
Methods of Organometallic and Inorganic Chemistry (Herrmann/
Brauer); Herrmann, W. A., Ed.; Georg Thieme Verlag: Stuttgart,
Germany, 1997; Vol. 8, p 5.
(16) Manzer, L. E. Inorg. Synth. 1982, 21, 135.
(17) Wender, I.; Sternberg, H. W.; Orchin, M. J . Am. Chem. Soc.
1952, 74, 1216.
(18) Calderazzo, F.; Pampaloni, G. Organomet. Synth. 1988, 4, 49.
(19) Calderazzo, F.; Pampaloni, G.; Zanazzi, P. F. Chem. Ber. 1986,
119, 2796.
(20) Herrmann, W. A.; O¨ fele, K.; Zybill, C. E. Introduction, Working
Techniques, Metal Carbonyls and Other Complexes. In Synthetic
Methods of Organometallic and Inorganic Chemistry (Herrmann/
Brauer); Herrmann, W. A., Ed.; Georg Thieme Verlag: Stuttgart,
Germany, 1997; Vol. 7, p 16.
(21) Hieber, W.; Schuster, L. Z. Naturforsch. 1957, 12B, 478; 1958,
13B, 339.
(c) n Bu 4N[V(CO)6]. A yellow solution of nBu4N[V(CO)6]
(0.202 g, 0.44 mmol) in toluene (30 mL) was treated with solid
[VCp2]BPh4 (0.217 g, 0.43 mmol). An infrared spectrum of the
solution, recorded 10 min after the reagents were mixed,
showed absorptions at 2043 m, 1969 w- m, 1896 vs, 1865 s,
1851 s, and 1653 m-s cm-1. After 24 h of stirring at room
temperature, the solution showed the absorption at 1851 cm-1
to be the most intense in the carbonyl stretching region. Two
weak absorptions were observed at 2052 and 2008 cm-1
.
[VCp 2(CO)2][Co(CO)4]: Cr ysta l Str u ctu r e Solu tion a n d
Refin em en t. Yellow transparent plates were obtained from

2454 Organometallics, Vol. 18, No. 13, 1999
Calderazzo et al.
Ta ble 1. La ttice Con sta n ts a n d P a r a m eter s of th e
Str u ctu r e Deter m in a tion of [VCp 2(CO)2][Co(CO)4]
(c) P h 3Sn Cl. Ph3SnCl (0.07 g, 0.17 mmol) was added to a
solution of VCp2Co(CO)4 (0.06 g, 0.17 mmol) in toluene (5 mL).
The blue solution that was obtained was evaporated to
dryness, and heptane (10 mL) was added. The solution thus
formed contained Ph3SnCo(CO)4 (IR (heptane): 2087 s, 2027
s, 1999 vs cm-1) only.25 The solid was analytically identified
as VCp2Cl16 (IR spectrum and Cl analysis).
(d ) Alk yn es. A solution of VCp2Co(CO)4 (0.38 g, 1.08 mmol)
in toluene (25 mL) was treated with an excess of the alkyne
(but-2-yne or hexafluorobut-2-yne). A rapid reaction took place
with formation of Co2(CO)6(alkyne), which was identified
spectroscopically (IR (toluene) for but-2-yne26 2070 m, 2046 s,
2022 s cm-1; IR (toluene) for hexafluorobut-2-yne27 2122 w,
2089 s, 2063 vs cm-1). All attempts to identify the vanadium
species failed.
compd
formula
mol wt
[VCp2(CO)2]Co(CO)4
C16H10CoO6V
408.13
cryst dimens (mm)
temp (K)
space group
cell constants
a (Å)
0.50 × 0.50 × 0.08
203
P1h (No. 2)
13.81(1)
b (Å)
14.065(3)
c (Å)
9.238(9)
R (deg)
93.63(4)
94.63(8)
66.36(4)
1637(2)
â (deg)
γ (deg)
volume (Å3)
Z
4
(e) CO. A solution of VCp2Co(CO)4 (0.04 g, 0.11 mmol) in
THF (5 mL) was treated with CO at atmospheric pressure:
the IR spectrum in THF solution showed absorptions at 2047
s, 1998 s, and 1887 vs cm-1, typical of [VCp2(CO)2][Co(CO)4].
Rea ction of VCp *2 w ith Co2(CO)8; Syn th esis of Cp *2V-
(µ-CO)Co(CO)3 (8). VCp*2 (0.37 g, 1.15 mmol) was added to
a solution of Co2(CO)8 (0.20 g, 0.58 mmol) in toluene (25 mL).
A fast reaction took place, affording a dark red solution. After
treatment with heptane (25 mL) black crystals were obtained,
which were isolated by filtration and dried in vacuo (0.12 g,
21% yield). The compound was analytically and spectroscopi-
cally identified as Cp*2V(µ-CO)Co(CO)3. Anal. Found (calcd)
for C24H30CoO4V: C, 57.3 (58.5); H, 5.9 (6.1). IR (toluene): 2000
s, 1934 vs, 1757 m-s cm-1. IR (THF): 2000 s, 1930 vs, 1887
m-s, 1766 m-s cm-1. IR (PCTFE mull): 2961 w, 2920 m, 2855
w, 1998 s, 1978 m-s, 1952 s, 1932 s, 1899 vs, 1880 vs, 1778 s,
D
calcd (g cm-3
)
1.655
15.90
816.0
µ (cm-1
F(000)
)
data collecn range (θ, deg)
3-25
scan type
ω
no. of measd rflns
abs cor
6922
numerical
no. of indep rflns in refinement
no. of refined params
Ra
Rw
GOF
3976 (with positive intensity)
433
0.072
0.057
1.045
b
a
b
R ) ∑|∆F|/∑|Fo|, for reflections with I > 1.0σ(I).
Rw )
[∑w(∆F)2/∑w|Fo| ]1/2; w ) 1/σ2|Fo|.
2
10,11
a toluene solution of Cp2VCo(CO)4
after standing at ca. 0
1385 m-s cm-1
.
°C for a few days. The structure was determined at -20 °C by
using an ENRAF-Nonius CAD4 diffractometer with Mo KR
radiation (λ ) 0.71073 Å, graphite monochromator). Crystal
data, data collection parameters, and convergence results are
compiled in Table 1. The structure was solved using direct
methods(SHELXS-9322).
Rea ctivity of VCp 2Co(CO)4. (a ) H2O. A solution of VCp2-
Co(CO)4 (0.12 g, 0.34 mmol) in toluene (10 mL) was treated
with H2O (13 µL, 0.7 mmol) at 0 °C. The addition caused the
rapid formation of a green solid (0.09 g, 71% yield), which was
analytically and spectroscopically identified as [VCp2(OH2)]-
[Co(CO)4]. Anal. Found (calcd) for C14H12CoO5V: C, 45.2 (45.4);
H, 3.1 (3.2). IR (Nujol mull): 3595 w, 3108 vw, 3022 w-m, 1854
vs, 999 w, 808 s, 555 vs, 411 m cm-1. When the reaction was
performed with D2O, the IR spectrum showed the expected
shift of the water frequencies (IR (Nujol mull): 3109 w, 3022
w-m, 2654 m-w, 1855 vs, 1008 m, 809 s, 555 vs, 410 m cm-1).
Wavenumbers in italics refer to the absorptions which shift
on H/D substitution.
Rea ctivity of Cp *2V(µ-CO)Co(CO)3. (a ) THF . Cp*2V(µ-
CO)Co(CO)3 (0.05 g, 0.10 mmol) was dissolved in THF (5 mL).
The IR spectrum of the solution recorded immediately after
the addition of the solvent showed absorptions at 2000 s, 1930
s, 1887 vs, and 1776 m-s cm-1. The spectrum recorded 30 min
later showed only one main absorption at 1886 cm-1 due to
the [Co(CO)4]- anion.28
(b) CO. A freshly prepared solution of Cp*2V(µ-CO)Co(CO)3
(0.05 g, 0.10 mmol) in THF (5 mL) was treated with CO at
atmospheric pressure with fast formation of [VCp*2(CO)2][Co-
(CO)4], spectroscopically identified in solution (IR (THF): 2001
s, 1946 s, 1886 vs cm-1).
Attem p ted Rea ction of VCp2 w ith Mn 2(CO)10. VCp2 (0.15
g, 0.83 mmol) was added to a solution of Mn2(CO)10 (0.15 g,
0.38 mmol) in toluene (25 mL). Even after 1 h of heating at
60 °C, no reaction took place, as confirmed by the persistence
of the bands due to the carbonyl stretching vibrations of Mn2-
(CO)10 (IR (toluene): 2046 s, 2011 vs, 1981 m cm-1).20
Rea ction of VCp 2Cl w ith Na [Mn (CO)5]. Na[Mn(CO)5]
(0.11 g, 0.50 mmol) was added to a suspension of VCp2Cl (0.12
g, 0.55 mmol). A rapid reaction was observed with formation
of Mn2(CO)10, which was spectroscopically identified in solution
(IR (toluene): 2046 s, 2010 vs, 1981 m cm-1).20
(b) CF 3COOH. CF3COOH (0.2 mL, 2.3 mmol) was added
to a solution of VCp2Co(CO)4 (0.80 g, 2.27 mmol) in heptane
(50 mL). Immediately a violet solid precipitated out. The solid
was decanted from the solution, washed with heptane (3 × 5
mL), and dried in vacuo (0.52 g, 78% yield). It was analytically
and spectroscopically identified as VCp2(OOCCF3). Anal.
Found (calcd) for C12H10F3O2V: C, 48.9 (49.0); H, 3.4 (3.4). IR
(Nujol/PCTFE mull): 3091 w, 2957 w, 2930 w, 2857 vw, 2047
m, 1995 m, 1879 w-m, 1715 m-s, 1687 vs, 1417 s, 1207 vs, 1158
vs, 967 m-s, 805 s, 720 m-s, 549 vs, 409 m cm-1. The IR
spectrum of the solution showed strong absorptions at 2052
Resu lts a n d Discu ssion
Th e VCp 2/V(CO)6 System . Some years ago Calder-
azzo and Bacciarelli reported6f that the reaction of VCp2
with V(CO)6 in the presence of CO affords the ionic
[VCp2(CO)2][V(CO)6] (eq 1); when the same reaction was
carried out under nitrogen, only a mixture of products
and 2030 vs cm-1 typical of HCo(CO)4.23 Some Co2(CO)8 was
24
also present, as evidenced by the 2070 m-s, 2043 s, and 1857
m absorptions.
(22) Sheldrick, G. M. SHELXL-93, A Program for the Solution of
Crystal Structures; University of Go¨ttingen, Go¨ttingen, Germany,
1993.
(23) Moore, E. J .; Sullivan, J . M.; Norton, J . R. J . Am. Chem. Soc.
1986, 108, 2257.
(25) Patmore, D. J .; Graham, W. A. G. Inorg. Chem. 1967, 6, 981.
(26) Sternberg, H. W.; Greenfield, H.; Friedel, R. A.; Wotiz, J .;
Markby, R.; Wender, I. J . Am. Chem. Soc. 1954, 76, 1457.
(27) Boston, J . L.; Sharp, D. W. A.; Wilkinson, G. J . Chem. Soc. 1962,
3488.
(24) Hileman, J . C. Metal Carbonyls. In Preparative Inorganic
Reactions; J olly, W. L., Ed.; Wiley: New York, 1964; Vol. 1, p 77.
(28) Edgell, W. F.; Lyford, J ., IV; Barbetta, A.; J ose, C. I. J . Am.
Chem. Soc. 1971, 93, 6403.

Oxidation Products of Vanadocene
Organometallics, Vol. 18, No. 13, 1999 2455
Ta ble 2. CO Str etch in g F r equ en cies (cm -1) of Com p ou n d s Con ta in in g Isoca r bon yl Gr ou p s
compd
terminal CO
bridging CO
ref
Cp2V(µ-OC)V(CO)5
2042, 1969, 1897, 1865
2000, 1934, 1887
2032, 1945, 1890, 1857
2039, 1960, 1889, 1860
1948, 1863
2023, 1973, 1939, 1917, 1824
2030, 2010, 1934, 1903
1927, 1918, 1849, 1830
1920, 1830
1652
1757
1708
1684
1545
1798, 1761
1770
1623
1650
this work
this work
Cp*2V(µ-OC)Co(CO)3
Cp*2V(µ-OC)V(CO)5
12
29
30
31
32
33
34
35
(OC)5V(µ-CO)V(THF)4(µ-OC)V(CO)5
Cp2ZrMe(µ-OC)Mo(CO)2Cp
Cp*2Yb(THF)(µ-OC)Co(CO)3
[Cp*2Yb(µ-OC)2Mn(CO)3]2
Cp′2TiMe(µ-OC)Mo(CO)2Cpa
Cp2Ti(THF)(µ-OC)Mo(CO)2Cp
Cp2TiCl(µ-OC)[Co3(CO)9]
2088, 2076, 2018, 1996
1980
a
Cp′ ) C5(CH3)4dCH2.
was obtained. More recently, Trogler et al. reported that,
VCp2 + V(CO)6 + 2CO f [VCp2(CO)2][V(CO)6] (1)
in the absence of CO, decamethylvanadocene reacts with
V(CO)6 to give the crystallographically established
µ-isocarbonyl complex Cp*2V(µ-OC)V(CO)5 (eq 2).12
F igu r e 1. Proposed structure for Cp2V(µ-OC)V(CO)5,
containing a µ-isocarbonyl bridge.
VCp*2 + V(CO)6 f Cp*2V(µ-OC)V(CO)5
(2)
Sch em e 1
We have found that mixing VCp2 and V(CO)6 in
toluene, under an argon atmosphere, gives a dark brown
solution, whose IR spectrum in the carbonyl stretching
region, recorded immediately after mixing the reagents,
shows six absorptions at 2040 m, 1970 w-m, 1896 vs,
1864 s, 1849 s, and 1652 m-s cm-1. Slowly, a dark brown
solid forms, the IR spectrum of the solution showing a
progressive decrease in the intensity of the bands with
respect to the absorption at 1849 cm-1. After 24 h, the
spectrum showed several weak bands in the positions
cited above. The solid isolated had an IR spectrum in
agreement with that of [VCp2(CO)2][V(CO)6] (2051 m,
2010 m, and 1840 vs cm-1 (Nujol)), but the color of the
solid (dark brown; [VCp2(CO)2][V(CO)6] is orange) and
the C, H, N, and CO analysis clearly indicated that a
mixture of compounds was formed.
When a solution of VCp2 in toluene was treated with
V(13CO)6, the IR spectrum of the intermediate product
showed the expected shift to lower wavenumbers of the
CO stretching frequencies (1995 m, 1924 m, 1855 vs,
1818 m-w, 1811 s, 1613 m-s cm-1, to be compared with
2042 m, 1969 m, 1897 vs, 1865 s, 1849 m-s, 1652 m-s
cm-1 observed for the unlabeled compound). Further
treatment with 12CO afforded [VCp2(12CO)2][V(13CO)6]
as the only product, as suggested by the IR spectrum of
a solution in THF of the isolated orange solid, which
shows absorptions at 2046 m, 1999 m, and 1818 vs cm-1
.
The unlabeled compound, [VCp2(CO)2][V(CO)6], shows
absorptions at 2050, 2001, and 1860 cm-1, the last one
belonging to the [V(CO)6]- anion.6f This observation
indicates that during the formation of the cationic
[VCp2(CO)2]+ moiety no redistribution of the carbonyl
ligands between the two metal centers occurs. Thus,
cleavage of the V-O isocarbonyl linkage must precede
charge separation and CO addition to the cation thus
formed.
The initial IR spectrum of the solution in the carbonyl
stretching region (2042 m, 1969 m, 1897v s, 1865 s, and
1652 m-s cm-1) is comparable to that of Cp*2V(µ-OC)V-
(CO)5 (2032, 1945, 1890, 1857, 1708 cm-1).12 In particu-
lar, the absorption at 1652 cm-1 is well in the range of
the CO stretching frequencies generally observed for
isocarbonyl groups (Table 2). Addition of Lewis bases,
such as pyridine, DME, and CO, to the VCp2/V(CO)6
system directly after the mixing of the reagents causes
the immediate cleavage of the isocarbonyl bridge with-
out evolution of gas and probable formation of the ionic
derivatives [VCp2Ln][V(CO)6], as evidenced by the pres-
The intermediate isocarbonyl product can also be
obtained by treating a toluene suspension of Na[V(CO)6]
with VCp2Cl (eq 3). The reaction is fast, and the initially
brown solution shows the typical IR absorptions at 2042
m, 1969 w-m, 1897 vs, 1865 s, 1849 m-s, and 1652 m-s
ence of a strong IR absorption at ca. 1850 cm-1
.
Due to the fact that pure [VCp2(CO)2][V(CO)6] is
obtained under a CO atmosphere6f and that the treat-
ment of the toluene solution of the intermediate species
with CO produces pure [VCp2(CO)2][V(CO)6] (vide infra),
it is believed that a partial electron transfer from V(0)
to V(II) occurs within the thermally unstable intermedi-
ate. However, the covalent intermediate is not able to
evolve to the ionic product, unless some ligands are
present to complete the coordination of the [VCp2]+
cation. The counteranion [V(CO)6]- can partially de-
compose and provide the required carbonyl groups. The
overall reaction can be summarized as reported in
Scheme 1.
cm-1
.
VCp2Cl + Na[V(CO)6] f Cp2V(µ-OC)V(CO)5 + NaCl
(3)
In conclusion, we can state that the primary product
of these reactions is a µ-isocarbonyl complex like the
one reported in Figure 1, i.e., with a structure similar
to Cp*2V(µ-OC)V(CO)5.12
Th e VCp 2/[F eCp 2]+ System . The chemistry of the
previous section has clearly shown the impossibility of
isolating the unsolvated [VCp2]+ cation through oxida-
tion of VCp2 by V(CO)6.

2456 Organometallics, Vol. 18, No. 13, 1999
Calderazzo et al.
Ferrocenium salts have been largely used in these
laboratories as one-electron oxidizing agents in toluene
medium.14,36 We therefore decided to study the VCp2/
[FeCp2]+ system.
By reaction of VCp2 with the corresponding ferroce-
nium derivative in toluene the [VCp2]BR4 compounds
containing the 14-electron [VCp2]+ cation have been
obtained in high yields (eq 4). The compounds are gray-
F igu r e 2. Proposed structure for VCp2Co(CO)4.
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) in [VCp 2(CO)2][Co(CO)4]
VCp2 + [FeCp2]BR4 f [VCp2]BR4 + FeCp2 (4)
R ) Ph, 4-C6H4F
V(2)-centroid(1)
V(2)-C(2a)
V(2)-C(2b)
1.927
1.950(9)
1.947(9)
V(2)-centroid(2)
O(2a)-C(2a)
O(2b)-C(2b)
1.920
1.146(8)
1.130(9)
V(2)-C (av)
Co(4)-C(4) (av)
2.26
1.76
C(4)-O(4) (av)
1.16
green solids extremely sensitive to air. No satisfactory
elemental analyses could be obtained for these com-
pounds, but it was possible to characterize them ana-
lytically by measuring the amount of CO absorbed in
toluene during their conversion to the dicarbonyl com-
plexes [VCp2(CO)2]BR4. Absorption of CO up to a CO/V
molar ratio of ca. 2 was observed, and the resulting
products were identified from the IR spectrum in the
solid state (Nujol mull) or in THF solution.6f The [B(3,5-
C6H3(CF3)2)4]- derivative separated out as an intrac-
table oil, which however reacted with CO to give the
expected dicarbonyl derivative.
The formulation of the compounds isolated according
to eq 4 has been confirmed by some reactions performed
on [VCp2]BPh4. As a matter of fact, [VCp2]BPh4 promptly
reacts with [PPN]Cl or nBu4N[V(CO)6], giving VCp2Cl
or Cp2V(µ-OC)V(CO)5 (eqs 5 and 6); it is also reduced
by 1 equiv of CoCp2 in toluene to vanadocene (eq 7).
C(2a)-V(2)-C(2b)
87.8(4) C(4)-Co(4)-C(4) (av)
109.3
V(2)-C(2a)-O(2a) 176.3(9) Co(4)-C(4)-O(4) (av) 177.8
V(2)-C(2b)-O(2b)
177.9(7)
centroid(1)-V(2)-
centroid(2)
138.4
cally pure Cp2VCo(CO)4, which can be isolated and
safely handled in the solid state only at low temperature
(ca. 0 °C). The absence of absorptions due to bridging
carbonyls in the IR spectrum of Cp2VCo(CO)4 sug-
gests10,11 that Cp2VCo(CO)4 contains terminal carbonyl
groups only and a V-Co bond37 (see Figure 2). During
our attempts to crystallize this material from toluene-
heptane at -20 °C, orange crystals were isolated, which
were shown by IR spectroscopy and X-ray diffractometry
(vide infra) to be [VCp2(CO)2][Co(CO)4], clearly resulting
from partial decomposition of the anion.
Due to the fact that a previous report on the solid-
state structure of the [VCp2(CO)2]+ cation (as a BPh4
-
[VCp2]BPh4 + [PPN]Cl f VCp2Cl +[PPN][BPh4]
salt) was characterized by severe disorder,6h we decided
to study [VCp2(CO)2][Co(CO)4] by X-ray crystallography.
(5)
The structure of [VCp2(CO)2][Co(CO)4] consists of
[VCp2(CO)2]+ cations and [Co(CO)4]- anions with two
independent units in the unit cell. Due to the similarity
of the two independent units, reference will be made to
one of them only. The cobalt atom in the [Co(CO)4]-
anion has the expected tetrahedral coordination, with
very few deviations from the ideal geometry, the average
C-Co-C angle being 109.3° (Table 3); the average
Co-C and C-O bond distances are in the range of those
previously reported for the same anion.38 A view of the
[VCp2(CO)2]+ cation is shown in Figure 3. The V-C-O
angles in [VCp2(CO)2][Co(CO)4] are 176.3(9) and 177.9-
(7)° (161(5)° and 174(3)° in the [B(C6H5)4]- derivative6h).
The V-CCO bond lengths in [VCp2(CO)2][Co(CO)4] (1.949-
(9) Å, mean value) are in the range observed in terminal
carbonyls, such as [PPN][V(CO)6] (1.931(9) Å),39 VCp-
(CO)4 (1.91(3) Å),40 or [V(η5-indenyl)2(CO)2]BPh4 (1.975-
(10) Å).6d The centroid(1)-V-centroid(2) angle (138.4°)
is comparable to that in [V(η5-indenyl)2(CO)2]BPh4
(138.5(4)°)6d and is in the range 138-140°, which is
usually observed for VCp2 derivatives.9
[VCp2]BPh4 + [nBu4N][V(CO)6] f
Cp2V(µ-OC)V(CO)5 + [nBu4N][BPh4] (6)
[VCp2]BPh4 + CoCp2 f VCp2 + [CoCp2]BPh4 (7)
Th e VCp 2/Co2(CO)8 System . An earlier study of the
vanadocene/Co2(CO)8 system showed that the treatment
of a VCp′2 solution (Cp′ ) C5H5, C5H4CMe3, C5H4Co2-
Me, C5Me5, C5Me4Et) with Co2(CO)8 affords heterobi-
metallic compounds whose composition depends on the
substituents on the vanadocenes.10,11
In the framework of the present study, we have
reexamined the VCp2/Co2(CO)8 reaction, confirming the
results of Mo¨ıse and co-workers10,11 As a matter of fact,
the reaction between VCp2 and Co2(CO)8 at low tem-
perature is fast and affords high yields of spectroscopi-
(29) Schneider, M.; Weiss, E. J . Organomet. Chem. 1976, 121, 365.
(30) Marsella, J . A.; Huffmann, J . C.; Caulton, K. G.; Longato, B.;
Norton, J . R. J . Am. Chem. Soc. 1982, 104, 6360.
(31) Tilley, T. D.; Andersen, R. A. J . Chem. Soc., Chem. Commun.
1981, 985.
(32) Boncella, J . M.; Andersen, R. A. Inorg. Chem. 1984, 23, 432.
(33) Hamilton, D. M.; Willis, W. S.; Stucky, G. D. J . Am. Chem. Soc.
1981, 103, 4255.
(34) Merola, J . S.; Gentile, R. A.; Ansell, G. B.; Modrick, M. A.; Zentz,
S. Organometallics 1982, 1, 1731.
(35) Schmidt, G.; Ba¨tzel, V.; Stutte, B. J . Organomet. Chem. 1976,
113, 67.
(36) (a) Calderazzo, F.; Ferri, I.; Pampaloni, G.; Englert, U. Orga-
nometallics 1998, 16, 3100. (b) Calderazzo, F.; Pampaloni, G.; Tripepi,
G. Organometallics 1998, 16, 4943.
(37) Calderazzo, F.; Fachinetti, G.; Marchetti, F.; Zanazzi, P. F. J .
Chem. Soc., Chem. Commun. 1981, 181. Fachinetti, G.; Fochi, G.;
Funaioli, T.; Zanazzi, P. F. Angew. Chem., Int. Ed. Engl. 1987, 26,
680. Selent, D.; Beckhaus, R.; Bartik, T. J . Organomet. Chem. 1991,
405, C15. Brammer, L.; McCann, M. C.; Bullock, R. M.; McMullan, R.
K.; Sherwood, P. Organometallics 1992, 11, 2339.
(38) Bockman, T. M.; Kochi, J . K. J . Am. Chem. Soc. 1989, 111, 4669.
(39) Wilson, R. D.; Bau, R. J . Am. Chem. Soc. 1976, 96, 7601.
(40) Wilford, J . B.; Whitla, A.; Powell, H. M. J . Organomet. Chem.
1967, 8, 495.

Oxidation Products of Vanadocene
Organometallics, Vol. 18, No. 13, 1999 2457
Sch em e 2
IR spectrum shows absorptions typical of the isocarbo-
nyl derivative, and only after 30 min can a main band
at 1886 cm-1 be observed, indicative of the presence of
the [Co(CO)4]- anion.28,43
The reaction of either Cp2VCo(CO)4 or Cp*2V(µ-OC)-
Co(CO)3 with THF proceeds without evolution of gas (as
evidenced by gas volumetric measurements), therefore
ruling out any Co(0) f Co(-I)/Co(II) disproportionation
reaction after the formation of a neutral carbonyl
derivative; it can be concluded that THF promotes the
charge separation between the two organometallic frag-
ments of the V-Co heterobimetallic derivatives (Scheme
2), with probable formation of the THF-solvated cations
[VCp2(THF)2]+ and [VCp*2(THF)2]+, respectively.
Rea ctivity of th e Va n a d iu m /Coba lt System s. If
Cp2VCo(CO)4 contains a vanadium-cobalt bond, it
should be highly reactive and undergo easy cleavage of
the metal-metal bond. This bond can be anticipated to
be weak, due to the observation that V(CO)6 is mono-
nuclear and that the cobalt-cobalt bond in Co2(CO)8 has
been estimated to be 87.8 kJ /mol.44 Moreover, the
formation of [VCp2(CO)2][Co(CO)4] from VCp2Co(CO)4
indicates that the vanadium-cobalt bond in the latter
complex is cleaved by treatment with Lewis bases.
Previous studies6g suggested that in aqueous solution
the [VCp2]+ cation is present as the monoaquo complex
[VCp2(OH2)]+, even though no direct observation of this
species was made. For instance, the reaction of VCp2-
Cl2 with AgClO4 in water gives AgCl and a pale green
solution thought to contain [VCp2(H2O)n](ClO4)2;4 the
latter, after reduction, afforded a purple solution con-
taining a species with two unpaired electrons. Moreover,
the [VCp2(OH2)2]2+ cation, prepared by reaction of VCp2-
Cl2 with HPO2(OC6H5)2 in water, has been structurally
characterized.45
F igu r e 3. Molecular structure of the [VCp2(CO)2]+ cation
in [VCp2(CO)2][Co(CO)4].
F igu r e 4. Proposed structure for Cp*2V(µ-OC)Co(CO)3
containing a µ-isocarbonyl bridge.
It is interesting to compare the structure of the [VCp2-
(CO)2]+ cation with the isoelectronic neutral derivatives
of group 4 metals, MCp2(CO)2 (M ) Ti, Zr, Hf). For the
titanium and vanadium derivatives, the CCO-M-CCO
and the centroid-M-centroid angles are almost the
same (M ) Ti, 87.9(6) and 138.6°;41 M ) V, 87.8(4) and
138.4°, respectively). In the recently reported [TiCp2-
(CO)2]2+ dication, the OC-Ti-CO angle is 86.8°, as
calculated on the basis of the IR spectra.36b The M-CCO
and M-centroid average bond distances are longer in
the titanium derivative (2.030(11) and 2.025 Å41) than
in the vanadium analogue (1.949(9) and 1.924 Å), due
to the smaller ionic radius of vanadium(III) with respect
to titanium(II). When comparing the zirconium and
hafnium MCp2(CO)2 complexes with [VCp2(CO)2]+, it is
possible to anticipate longer bond distances (M-CCO: M
) Zr, 2.187(4) Å;6h M ) Hf, 2.16(2) Å42) and larger
angles (CCO-M-CCO: M ) Zr, 89.2(2)°; M ) Hf, 89.3-
(9)° 42), as expected on the basis of the greater ionic radii
of the 4d and 5d metals.
Addition of water to a cold solution of VCp2Co(CO)4
in toluene caused the immediate formation of a green
solid in a colorless solution. The solid was analytically
identified as the monoaquo adduct [VCp2(OH2)][Co-
(CO)4] (eq 9). The IR spectrum in the solid state shows
The reaction between VCp*2 and Co2(CO)8 affords a
black solid of composition VCp*2Co(CO)4 (eq 8) whose
IR spectrum in solution shows absorptions at 2000 s,
1930 vs, and 1766 s cm-1; the low-wavenumber absorp-
VCp2Co(CO)4 + H2O f [VCp2(OH2)][Co(CO)4] (9)
VCp*2 + Co2(CO)8 f Cp*2V(µ-OC)Co(CO)3 (8)
an absorption at 3595 cm-1 assigned to the O-H
stretching vibration of the coordinated water. By using
D2O, the band shifts to 2654 cm-1 as a consequence of
the isotopic substitution (ν˜OH/ν˜OD ) 1.35; the theoretical
value is 1.41).
The treatment of a solution of VCp2Co(CO)4 with CF3-
COOH afforded a violet compound, sparingly soluble in
toluene, which was identified as VCp2(O2CCF3). The IR
spectrum of the solution revealed the presence of HCo-
(CO)4. The reaction can, therefore, be described as in
tion suggests the presence of a bridging carbonyl, as
already observed in Cp*2V(µ-OC)V(CO)5 (1708 cm -1),
and therefore a similar structure can be envisaged for
the cobalt-vanadium compound (Figure 4). The methyl-
substituted derivative Cp*2V(µ-OC)Co(CO)3 is more
robust in solution than the nonmethylated analogue;
nevertheless, it slowly decomposes, as evidenced by the
formation of a solid together with the appearance in
solution of the absorptions typical of Co4(CO)12.10,11
The treatment of a freshly prepared toluene solution
of Cp*2V(µ-OC)Co(CO)3 with THF gives a solution whose
(43) Edgell, W. F.; Yang, M. T.; Koizumi, N. J . Am. Chem. Soc. 1965,
87, 2563.
(44) Pilcher, G.; Skinner, H. A. Thermochemistry of Organometallic
Compounds. In The Chemistry of Metal-Carbon Bond; Harley, F. R.,
Patai, S., Eds.; Wiley: Chichester, U.K., 1982; Vol. 2, p 43.
(45) Toney, J . H.; Brock, C. P.; Marks, T. J . J . Am. Chem. Soc. 1986,
108, 7263.
(41) Atwood, J . L.; Stone, K. E.; Alt, H. G.; Hrncir, D. C.; Rausch,
M. D. J . Organomet. Chem. 1977, 132, 367.
(42) Sikora, D. J .; Rausch, M. D.; Rogers, R. D.; Atwood, J . L. J .
Am. Chem. Soc. 1979, 101, 5079.

2458 Organometallics, Vol. 18, No. 13, 1999
Calderazzo et al.
Ta ble 4. Red ox P oten tia ls for V(CO)6, Mn 2(CO)10
Co2(CO)8, a n d [VCp 2]+
,
eq 10. The IR spectrum in the solid state of the violet
a
a
VCp2Co(CO)4 + CF3COOH f
compd
EOx/Red
ref
compd
EOx/Red
ref
VCp2(O2CCF3) + HCo(CO)4 (10)
Mn2(CO)10
[VCp2]+
-1.52
-1.10
47
48
Co2(CO)8
V(CO)6
-0.63
47
47
-0.14b
solid shows absorptions at 1687s and 1417m cm-1
,
a
All potentials are referred to the potential of a ferrocene/
b
respectively, due to the asymmetric and symmetric C-O
stretching vibrations of the trifluoroacetato group. Ad-
ditional bands at 1207 and 1158 cm-1 denote the
presence of CF3 groups. As far as the coordination mode
of the trifluoroacetato group is concerned, the separation
between the asymmetric and the symmetric C-O
stretching frequencies (∆) is consistent with unidentate
coordination,46 which is in agreement with the marked
tendency of the 14-electron [VCp2]+ species to attain at
least the 16-electron configuration, as shown by the
reactions with water (vide supra), acetone,9 or pyridine.6g
By reaction with Ph3SnCl the vanadium-cobalt bond
in VCp2Co(CO)4 was replaced by a tin-cobalt bond
together with formation of VCp2Cl (eq 11). Similar
ferrocenium couple at 0.400 V vs SCE. E(V(CO)6/[V(CO)6]-).
[VCp2]+/VCp2 couple is more positive than that of the
Mn2(CO)10/[Mn(CO)5]- couple and is observed at poten-
tials more negative than those of the Co2(CO)8/[Co-
(CO)4]- and V(CO)6/[V(CO)6]- couples. A determining
factor in the failure to observe reaction 12a is connected
with the presence of a manganese-manganese bond
(BDE ) 158 kJ /mol49) which is considerably stronger
than that of Co2(CO)8 (BDE ) 87.8 kJ /mol44).
Con clu sion s
The reaction of vanadocene with [FeCp2]+ in toluene
gives the unsolvated [VCp2]+ cation, which has been
isolated and characterized for the first time both by
analysis and by studying its reactivity toward Lewis
bases such as chloride ions or reducing agents such as
cobaltocene. Moreover, this study has shown that the
oxidation of VCp2 by V(CO)6 occurs under argon via the
intermediate formation of an unstable isocarbonyl de-
rivative, which has been identified in solution by IR
spectroscopy as Cp2V(µ-OC)V(CO)5.
Ph3SnCl + VCp2Co(CO)4 f
VCp2Cl + Ph3SnCo(CO)4 (11)
compounds, containing main-group-metal-cobalt bonds,
of the type R3MCo(CO)4, were obtained from the reac-
tion of Co2(CO)8 in methanol with R3MCl (R ) Me, Ph;
M ) Ge, Sn, Pb) systems.25
Th e VCp 2/Mn 2(CO)10 System . When a solution of
VCp2 was placed in contact with Mn2(CO)10, no reaction
took place, even after heating at ca. 60 °C (eq 12a). On
A detailed study of the reactivity of VCp2Co(CO)4 has
shown that this compound undergoes charge separation
on addition of Lewis bases such as CO, THF, py, H2O,
and CF3COOH, affording either ionic or neutral deriva-
tives of general formula [VCp2Ln]0/+
.
VCp2 + 1/2Mn2(CO)10 N [VCp2][Mn(CO)5] (12a)
Ack n ow led gm en t. We thank the Consiglio Nazio-
nale delle Ricerche (CNR, Roma), Progetto Strategico
Metodologie Innovative, for financial support. I.F. thanks
the ENI for financial support during her studies at the
Scuola Normale Superiore (Pisa) in fulfillment of the
requirements for the Ph.D. program.
VCp2Cl + Na[Mn(CO)5] f
VCp2 + Mn2(CO)10 + NaCl (12b)
the other hand, when solid Na[Mn(CO)5] was added to
a solution of VCp2Cl in toluene, a rapid reaction was
observed and the IR spectrum of the solution showed
the presence of Mn2(CO)10 (eq 12b). It seems therefore
that VCp2, which smoothly reduces both V(CO)6 and
Co2(CO)8, is not a strong enough reducing agent for Mn2-
(CO)10. This finding is in agreement with the values of
the reduction potentials recently obtained in an elec-
trochemical study on CoCp2/metal carbonyl systems
(Table 4).47 In fact, the reduction potential of the
Su p p or tin g In for m a tion Ava ila ble: Tables of structural
data for [VCp2(CO)2][Co(CO)4], including positional parameters
of non-hydrogen atoms, positional parameters of hydrogen
atoms, all bond distances and angles, and displacement
parameters. This material is available free of charge via the
Internet at http://pubs.acs.org.
OM9809320
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