COMMUNICATION
À
Acetonitrile is
chemistry, which can coordinate to a metal center as a weak
ligand. The acetonitrile C CN bond is usually inert to tran-
sition metals because it has a rather strong C CN bond
energy (133 kcalmol ) compared to an alkane C C bond
energy (ca. 83 kcalmol ). Accordingly, acetonitrile C CN
bond cleavage mediated by transition metals has rarely been
explored.[1] However, if acetonitrile, the most widely used
organonitrile, is able to act as a nitrile source by C–CN acti-
vation, this strategy would be of great interest for the devel-
opment of new cyanation reactions and avoidance of highly
toxic metal cyanides (such as KCN, NaCN, CuCN, Zn(CN)2,
TMSCN, etc.).[2]
a
common solvent in organometallic
mediated C CN bond cleavage of nitriles, most of them
remain stoichiometric reactions not catalytic processes. In ad-
dition, it is known that acetonitrile-coordinated [Cu-
À
(CH3CN)4]+ or [Cu(CH3CN)4]2+ species are stable and
ACHUTGTNRENNUG CAHTUNGTRENNUGN
À
À1
À
often used as a starting reagents in the synthesis of other
copper complexes.[15] Consequently, tremendous challenges
À1
À
À
for acetonitrile C CN bond cleavage lie ahead in activating
stable acetonitrile and achieving a catalytic reaction with
cheap copper species. Herein, we report a novel Cu-cata-
lyzed acetonitrile C CN bond cleavage/aromatic C H bond
activation to furnish new C CN bonds with the assistance of
À
À
À
disilane (Scheme 1).
À
In recent years, C C bond activation has been a challeng-
ing topic in modern organic chemistry.[3] Organonitriles serv-
À
ing as a nitrile source by C CN cleavage is an appealing yet
challenging strategy. Since Murahashiꢁs discovery of the Pd-
catalyzed decarbonylation of acyl cyanides in 1986,[4] prog-
À
ress in C CN cleavage mediated by transition-metal com-
plexes,[1c] such as Pd,[5] Ni,[6] Rh,[7] Fe,[8] and others[9] has
been made. Nevertheless, most of these cases focused on ar-
omatic nitriles or acyl cyanides which are very easily
À
cleaved. Mechanistic studies regarding the C CN bond scis-
sion using [Ni
A
À
Scheme 1. Proposed process for transition-metal-mediated C CN cleav-
age.
phino)ethane) have been done by Jones and co-workers.[10]
Inspired by these pioneering works, we imagined that aro-
À
matic C H cyanation by using acetonitrile as a nitrile source
À
may be accessed under a copper complex that is one of the
most inexpensive metals. However, to the best of our knowl-
edge, only a few examples have been reported regarding the
Initially, we found that the C H bond cyanation of 2-phe-
nylpyridine 1a was encountered in the presence of acetoni-
trile solvent and 20 mol% CuACHTUNRGTNEUNG(OAc)2 under oxygen at
À
copper-promoted C CN cleavage. In 2001, Mascharak and
1508C. Surprisingly, a 44% yield of cyanated products was
obtained after 5.5 days [Eq. (1)]. It is possible that the
cyano group on the phenyl ring in the corresponding prod-
ucts originates from acetonitrile. A control experiment in
the absence of metal catalyst resulted in recovery of 1a
(Table 1, entry 1). Among a number of ligands examined,
N,N,N’,N’-tetramethylethylenediamine (TMEDA) could
slightly shorten the reaction time to four days and increase
the yield to 51% (Table 1, entry 2; see the Supporting Infor-
mation for details). However, the reaction still took place
slowly.
co-workers first discovered that [Cu
N
N,N’-dimethylpyridine-2,6-dicarboxamide anion; en=ethyle-
À
nediamine) could break the acetonitrile C CN bond by het-
erolytic cleavage to form CNÀ and CH3 fragments, which
+
could be trapped and detected.[11] After that, a dinuclear
À
copper(II) cryptate-mediated C C bond activation of aceto-
nitrile by an SN2-type process was demonstrated by Lu.[12]
Recently, Wang and co-workers reported cyanation of
arenes by using benzyl nitrile as a cyanide anion surrogate
in the presence of 1.2 equivalents of CuBr.[13a] Very recently,
a Cu/Ag system for the cyanation of aryl iodides with aceto-
nitrile has been documented by Li.[14a] Although these mech-
anistic investigations and reactions open a new door for Cu-
[a] M. Zhao, X. Qiao, Y. Zhu, Prof. Dr. Z. Shen
School of Chemistry and Chemical Engineering
Shanghai Jiao Tong University
800 DongChuan Road, Shanghai, 200240 (China)
Fax : (+86)21-54741297
À
We thought that increasing the rate of C CN cleavage
À
might be possible by changing the mode of C CN bond acti-
[b] X. Kou, X. Tong
vation. Based on previous mechanistic studies, transition-
Key Laboratory for Advanced Materials and
Institute of Fine Chemicals
East China University of Science and Technology
Shanghai 200237 (China)
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metal-mediated C CN bond scission reactions have re-
vealed two distinct pathways (Scheme 1, paths a and b).[5–9]
À
One is the oxidative addition of a C CN bond to an air-sen-
sitive low-valent metal center to afford an alkyl
N
Supporting information for this article is available on the WWW
complex (path a).[5–6] Another one is a low-valent metal with
Chem. Eur. J. 2013, 19, 16880 – 16886
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
16881