reduction of 1 and 2 causes dechelation of dmbbbpy, the
resultant five-coordinate Ru and monodentate dmbbbpy may
2
(
(
a)
b)
provide two binding sites for an attack of CO
facilitate a coupling reaction of CO affording oxalate. Thus,
dmbbbpy of 1 and 2 greatly contributes to the first selective
2
, which would
2
22
2
2
depending upon the absence
O, respectively, in the electrochemical
formation of C
and the presence of H
reduction of CO
2
O
4
and HCO
2
2
.
This work was partly supported by Grant-in-Aid for Scien-
tific Research on Priority Areas (No. 283, ‘Innovative Synthetic
Reactions’) from Monbusho, and the authors also thank
Monbusho for a scholarship (to M. M. A.).
(
c)
Footnotes and References
*
E-mail: ktanaka@ims.ac.jp
† HCO
H was characterized using an isotachophoretic analyzer and 13C
NMR spectroscopy.
Oxalate was characterized using an isotachophoretic analyzer [GC–MS
1
800
1700
n / cm
1600
1500
2
~
–1
‡
Fig. 2 IR spectra of 1 (0.8 mm) during a thin-cell bulk electrolysis in CD
with LiBF . (a) Starting scan, (b) using CO , (c) using CO .
4 2 2
3
CN
13
(diester derivative, by esterification with diazomethane)] and C NMR
1
2
13
spectroscopy.
§
Electrolysis of 1 at potentials more negative than 21.75 V resulted in
Fig. 2(c)]. The bands at 1638 and 1540 cm21 also disappeared
upon reoxidation at 20.70 V suggesting that a CO adduct
probably formed by an attack of two molecules of CO to the
two-electron reduced form of 1 which acts as a precusor to
rapid growth of the 1633 cm21 band so that electrolysis was conducted at
[
1.65 V to detect the emergence of the 1684 and 1603 cm2 bands
1
2
2
clearly.
[Ru(bpy)
characterized by electrospray MS and elemental analyses.
2
¶
L]2+ (L = 2-pyridyl-1-methylbenzimidazole) was prepared and
2
oxalate in the electrochemical reduction of CO
MeCN.
2
in dry
1
2
F. Hutschka, A. Dedieu, M. Eichberger, R. Fornika and W. Leitner,
J. Am. Chem. Soc., 1997, 119, 4433.
P. G. Jessop, Y. Hsiao, T. Ikaiya and R. Noyori, J. Am. Chem. Soc.,
1996, 118, 352.
It is noteworthy that any interaction between reduced forms
2+
of [Ru(bpy)
azole¶) and CO
Indeed, these complexes have no ability to catalyze the
electrochemical reduction of CO under controlled potential
electrolysis even at 21.80 V in the absence or presence of H
2
L] (L = bpy or 2-pyridyl-1-methylbenzimid-
2
was not observed at all in the CV in MeCN.
3 W. Leitner, Angew. Chem., Int. Ed. Engl., 1995, 34, 2207; P. G. Jessop,
T. Ikaiya and R. Noyori, Chem. Rev., 1995, 95, 259.
2
4
5
6
K. M. Lam, K. Y. Wong, S. M. Yang and C. M. Che, J. Chem. Soc.,
Dalton Trans., 1995, 1103; H. Nakajima, T. Mizukawa, H. Nagao and
K. Tanaka, Chem. Lett., 1995, 251.
A. M. Herring, B. D. Steffy, A. Miedaner, S. A. Wander and
D. L. DuBois, Inorg. Chem., 1995, 34, 1100; R. Fornica, B. Seemann
and W. Leitner, J. Chem. Soc., Chem. Commun., 1995, 1479.
P. G. Jessop, T. Ikaiya and R. Noyori, Nature, 1994, 368, 232;
M. Collomb-Dunand-Saider, A. Deronizer and R. Ziessel, J. Chem.
Soc., Chem. Commun., 1994, 189.
2
O
n+
in MeCN. Moreover, [Ru(bpy)
=
2
(CO)X] (n = 2, X = CO; n
1, X = Cl) works as an effective catalyst producing CO and/
or HCO H in the electrochemical reduction of CO under protic
conditions, but the complex readily decomposes in the similar
reduction of CO in the absence of proton donor. Sav e´ ant and
9
2
2
2
coworkers have shown that aromatic nitriles and esters with
redox potentials more negative than 21.93 V mediate electro-
chemical reduction of CO
explained by an electrophilic attack of CO
2
affording oxalate. The reaction is
7 Y. Kushi, H. Nagao, T. Nishioka, K. Isobe and K. Tanaka, J. Chem.
Soc., Chem. Commun., 1995, 1223; Y. Kushi, H. Nagao, T. Nishioka,
K. Isobe and K. Tanaka, Chem. Lett., 1994, 2176.
2
to oxygen or
nitrogen of the anion radicals followed by homolytic cleavage
8
H. Nakajima, Y. Kushi, H. Nagao and K. Tanaka, Organometallics,
995, 14, 181.
I. Ishida, K. Tanaka and T. Tanaka, Organometallics, 1987, 6, 181.
2
2
[X = OC(O)R, CN] bond and the subsequent
of the ArX–CO
coupling of free CO
2
showed the two n(CO ) bands (1684, 1603 cm ) assignable
1
.
2 10
2
.
On the other hand, the IR spectra of
9
1
2
1
1
0 A. Gennaro, A. A. Isse, J.-M. Saveant, M.-G. Severin and E. Vianello,
J. Am. Chem. Soc., 1996, 118, 7190.
to the precursor for oxalate under electrolysis at 21.65 V,
suggesting that oxalate generation in the present study does not
.
2
result from dimerization of free CO
2
. If two-electron
Received in Cambridge, UK, 13th October 1997; 7/07363A
250
Chem. Commun., 1998