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R. Tuba et al. / Journal of Molecular Catalysis A: Chemical 236 (2005) 113–118
catalytic cycle can be closed by regeneration of 3 and 4
from Co2(CO)7(PPh3) and [Co(CO)3(PPh3)2][Co(CO)4] or
Co2(CO)6(PPh3)2 by the reaction with ethyl diazoacetate.
Experimental evidence for both steps of such a mecha-
nism has been described in the literature in the case of
Co2(CO)6(dppm). First, the reaction of Co2(CO)6(dppm)
with ethyl diazoacetate gives the carbene complex Co2(CO)5
(CHCO2Et)(dppm), along with CO and N2 [20]. Second,
the reaction of Co2(CO)5(CHCO2Et)(dppm) with CO and
CD3OD give EtO2CCH C O, EtO2CCHDCO2CD3 and
Co2(CO)6(dppm) [21], through the assumed intermediate.
was stirred in an atmosphere of carbon monoxide at room
temperature for 1 h. Addition of triphenylphosphane (2.63 g,
10 mmol) and stirring the mixture for 10 min resulted in
gas evolution and the formation of a cherry-red solution
with a flaky precipitate. Filtration under argon and crystal-
lization at −40 ◦C gave 3 as 0.1–0.4 mm size purple-red
crystals (1.84 g, 38%). (A second crop or a longer triph-
enylphosphane addition procedure gave a less attractive
grayish-red solid product!) 3, IR (CH2Cl2) ν(C O) 2080
(εM = 1316 cm2/mmol), 2033 (εM = 2773 cm2/mmol), 2013
(εM = 2578 cm2/mmol), ν(C O) 1829 (εM = 565 cm2/mmol),
1688 (εM = 174 cm2/mmol), 1666 (εM = 151 cm2/mmol)
cm−1. IR (KBr) ν(C O) 2075 (s), 2027 (s), 2017 (s), 2005
(s), 1990 (s), ν(C O) 1825 (s), 1668(m) cm−1. Analysis:
calculated for C28H21O8Co2P: C, 53.02; H, 3.34, Co, 18.58;
3. Experimental
3.1. General comments
1
P, 4.88. Found: C, 52.86; H, 2.99; Co, 18.48; P, 4.80. H
NMR (CDCl3) δ 1.26 (t, 3H), 4.12 (q, 2H), 5.66 (s, 1H),
7.42–7.52 (m, 15H) ppm. 13C NMR (CDCl3) δ 14.22 (CH3),
60.80 (CH2), 91.40 (CH), 130.85–133.39 (C6H5), 180.31
(org. CO), 200.97 (term. CO) ppm. 13C NMR (solid state)
δ 14.42 (CH3), 60.14 (CH2), 90.54 (CH), 130.30 (C6H5),
180.63 (org. CO), 208.99 (term. CO) ppm. 31P NMR (CDCl3)
δ 49.74 ppm.
Handling of Co2(CO)8 and other carbonyl cobalt com-
plexes was carried out in an atmosphere of dry (P4O10) and
deoxygenated (BTS contact, room temp.) argon or carbon
monoxide utilizing standard Schlenk techniques [22]. Sol-
vents were dried and distilled under an atmosphere of argon
or carbon monoxide according to standard procedures [23].
IR spectra were recorded on a Thermo Nicolet Avatar 330
FTIR spectrometer using 0.00265, 0.00765, or 0.02153 cm
CaF2 solution cells, calibrated by the interference method
[24]. Gas chromatographic analyses were performed on a
HP 5890 instrument with FID, using a SPB 1 30 m, 0.32 m
column and n-nonane was used as an internal standard. 1H,
13C, and 31P NMR spectra were recorded on a Varian Unity
using CDCl3 as the solvent. Chemical shifts δ are reported in
ppm, for 1H and 13C relative to CHCl3 (7.26 and 77.00 ppm,
respectively) and for 31P relative to H3PO4. Octacarbonyl di-
cobaltwaspreparedbyaliteratureprocedure[25], andwasre-
crystallized twice in an atmosphere of carbon monoxide, first
from CH2Cl2 and then from n-heptane. All other reagents and
solvents were obtained from Sigma–Aldrich. The gas volume
change in reactions at atmospheric pressure was determined
using a thermostatted glass reactor having an inner volume
of 55 cm3, which was connected to a thermostatted mercury-
reactant into the reactor as a stock solution, using a Hamilton
TLL syringe, through a silicon disk port. Reactions under 50
bar CO pressure were performed in a stainless-steel autoclave
with a glass liner (total capacity = 12.8 cm3) [26]. Microanal-
yses were performed using a CHNSO EA1108-Elemental
Analyser (Carlo Erba). Cobalt and phosphorus analyses were
performed using established micro analytical methods.
3.3. Preparation of Co2(CO)5(CHCO2Et)(PPh3)2,
[µ2-{ethoxycarbonyl(methylene)}-µ2-(carbonyl)-
bis(triphenylphosphane-dicarbonyl-cobalt) (Co Co)] (4)
3.3.1. Method A
A solution of Co2(CO)8 (0.59 g, 1.72 mmol) and ethyl dia-
zoacetate (0.63 cm3, 6.00 mmol) in n-pentane (140 cm3) was
stirred in an atmosphere of argon at room temperature for
1 h. Addition of triphenylphosphane (1.38 g, 5.26 mmol) and
stirring the mixture for 15 min resulted in the formation of
a light yellow solution and a brick-red precipitate. Filtration
under argon gave 4 as a red powder (1.48 g, 99%).
3.3.2. Method B
Addition of triphenylphosphane (2.0 g, 7.63 mmol) un-
der argon to a stirred, filtered solution obtained from
Co2(CO)8 (2.61 g, 7.63 mmol), ethyl diazoacetate (0.8 cm3,
7.62 mmol) and triphenylphosphane (2.63 g, 10 mmol) in n-
pentane (200 cm3) as described above in the preparation of
3, gave, within 10 min, a pale yellow solution and a brick-
red precipitate. Filtration under argon gave 4 as a red powder
(4.64 g, 70%).
4, IR (CH2Cl2) ν(C O) 2040 (εM = 1181 cm2/mmol),
2005 (εM = 2710 cm2/mmol), 1983 (εM = 2050 cm2/mmol),
1970 (εM = 1869 cm2/mmol), ν(C O) 1786 (εM = 506 cm2/
mmol), 1678 (εM = 205 cm2/mmol), cm−1. IR (KBr) ν(C O)
2034 (m), 2003 (s), 1980 (s), 1964 (s), ν(C O) 1790 (s),
1674 (m) cm−1. Analysis: calculated for C45H36O7Co2P2:
C, 62.23; H, 4.18, Co, 13.57; P, 7.13. Found: C, 61.85; H,
3.2. Preparation of Co2(CO)6(CHCO2Et)(PPh3),
[µ2-{ethoxycarbonyl(methylene)}-µ2-(carbonyl)-
(tricarbonyl-cobalt)-(triphenylphosphane-dicarbonyl-
cobalt) (Co Co)] (3)
1
4.03; Co, 13.23; P, 6.82. H NMR (CDCl3) δ 1.02 (t, 3H),
A solution of Co2(CO)8 (2.61 g, 7.63 mmol) and ethyl
3.77 (q, 2H), 4.35 (t, J(31P-1H = 7.7 Hz),1H), 7.31–7.51 (m,
15H) ppm. 13C NMR (CDCl3) δ 14.16 (CH3), 60.13 (CH2),
diazoacetate (0.8 cm3, 7.62 mmol) in n-pentane (200 cm3)