Russian Chemical Bulletin, International Edition, Vol. 50, No. 12, pp. 24832484, December, 2001
2483
Electron transfer-induced replacement of carbonyl ligands
in cobalt clusters
V. A. Koneva and V. V. Krivykh«
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5085. E-mail: vkriv@ineos.ac.ru
Scheme 2
Activation of carbonyl clusters through their oxida-
tion for the replacement of carbonyl ligands is not
documented. This is due to their high oxidation poten-
+
e
tial and the instability of the resulting radical cations.1
In the present work, we proposed a new approach to the
replacement of carbonyl ligands involving the oxida-
tion of an electroactive organometallic group linked
through a conducting chain to the cluster frag-
ment rather than the cluster itself. Derivatives 1 in
which the electroactive group2 Cp*(dppe)Fe is linked
by the acetylenide bridge with a Co2C2-type clus-
ter were chosen as the starting compounds. These
complexes were prepared by the standard procedure3
(Scheme 1).
Cp*(dppe)FeC CC2R[Co2(CO)6]
1a,b
[1a,b]+
20 °C dppm
+
80 °C dppm
Cp*(dppe)FeC CC2R[Co2(CO)4dppm]
[2a,b]+
+e
Cp*(dppe)FeC CC2R[Co2(CO)4dppm]
Scheme 1
2a,b
Cp*(dppe)FeC≡CC≡CR + Co2(CO)8
Cp*(dppe)FeC≡CC2R[Co2(CO)6]
1à,b
Thus, the present work demonstrated the potentiality
of this approach, which can serve as a model of molecu-
lar devices for a switch-on (oxidation)switch-off (re-
R = H (a), SiMe3 (b)
duction) scheme.
All manipulations relating to the synthesis and isolation
were carried out in an atmosphere of argon with the use of
anhydrous solvents. IR spectra were recorded on a Magna 750
instrument (Nikolet) (resolution 2 cm1) in CH2Cl2. NMR
spectra were recorded on a Bruker AMX-400 instrument
(400.13 MHz) with (1H) Me4Si as the internal standard
and (31P) 85% H3PO4 as the external standard. ESR
spectra were recorded on a Varian E-12 spectrometer
equipped with a double resonator (for a test sample and a
standard).
[(Pentamethylcyclopentadienyl)(bisdiphenylphosphino-
ethane)iron(II)]bis(diphenylphosphinomethane)tetracarbonyl-
dicobalt](µ-η1,η2-butadiynyl) (2a) was obtained by oxidation
of compound 1a (0.0185 g, 0.02 mmol) with Cp2FeBF4
(0.0055 g, 0.02 mmol) in 5 mL of CH2Cl2 over 20 min
followed by addition of dppm (0.0077 g, 0.02 mmol) and
stirring at ∼20 °C for 1.5 h. A solution of Cp2Co (0.0038 g,
0.02 mmol) in 2 mL of CH2Cl2 was added to the reaction
mixture, and stirring was continued for an additional hour.
The solvent was removed in vacuo, and the products were
extracted with hexane. The extract was filtered under argon
through a layer of Celite and kept in a refrigerator. The black-
It was found that the oxidation of compound 1 with
Cp2FeBF4 gives labile radical cations [1a,b]+ (IR,
ν/cm : 2096, 2062, 2038 (s, CO); ESR, g = 2.26). The
1
addition of diphenylphosphinomethane (dppm) to radi-
cal cation [1a,b]+ causes replacement of two carbo-
nyl ligands under mild conditions and gives rise to
stable radical cations [2a,b]+ (Scheme 2), which
can be isolated in the individual state. One-pot
reduction of radical-cation complexes [2a,b]BF4
with Cp2Co yielded neutral diamagnetic compounds
2a,b. The total yield of the conversion 1a,b → 2a,b
was ∼70%.
Complexes 2a,b were characterized by data from
elemental analysis, IR spectroscopy, and 1H and
31P NMR spectroscopy. Although complexes 2a,b can
be obtained from compounds 1a,b in one step, this
conversion requires more drastic conditions and pro-
vides significantly lower yields because of the formation
of decomposition products.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 23682369, December, 2001.
1066-5285/01/5012-2483 $25.00 © 2001 Plenum Publishing Corporation
Koneva
