DOI: 10.1002/chem.201101930
À
À
Nickel-Catalyzed C P Cross-Coupling by C CN Bond Cleavage
[
a]
Meng Sun, Hong-Yu Zhang, Qi Han, Kuo Yang, and Shang-Dong Yang*
Selective CÀC s-bond activation (cleavage) by transition-
metal complexes is one of the most challenging subjects in
organometallic chemistry. This is due not only to its funda-
mental scientific interest, but also its potential utility in or-
bond cleavage and our recent report of copper-catalyzed CÀ
[10]
P coupling through decarboxylation,
we have explored
the phosphination of aryl nitriles through CÀCN bond acti-
II
vation. Here, we disclose the first example of Ni -catalyzed
[1]
ganic synthesis. In general, this transformation depends
heavily on either the release of ring strain or aromatization
to provide the substantial driving force and thus lacks gener-
CÀP coupling by CÀCN bond cleavage for the synthesis of a
variety of phosphorus ligands (Scheme 1, Path D). As a
practical alternative, this methodology exhibits several very
attractive features: 1) aryl nitriles are cheap, stable, and
readily available in various structures; 2) the cyano group
ensures the regioselectivity of the reaction; 3) namely the
simple setup, mild conditions, and attractive scale-up possi-
bilities.
[2]
ality. As an exception, CÀCN s-bond cleavage has gained
significant attention due to the kinetically favorable interac-
1
2
tion of metals with a cyano group through h - or h -coordi-
[3]
nation and the resultant highly stable metal–CN bond as a
[4]
thermodynamic driving force. To date, CÀCN cleavage has
mainly focused on CÀC bond formation by carbocyanation
In an initial study, we chose 2-cyanonaphthalene 1a and
Me SiPPh as the model substrates to begin our investiga-
[5]
of alkynes and olefins, cross-coupling with metal reagents
3
2
[6]
(
Scheme 1, Path A). In addition, Chatani and co-workers
tion. Because monophosphorus or P, N bidentate ligands are
key to many metal-catalyzed or-
ganic transformations, including
[11]
many chiral reactions. On the
other hand, the pioneering re-
ports of Bergman, Brookhart,
and Chatani have shown that
the silicon can assist in cleavage
of the CÀCN bond through a
[8,12]
silyl–rhodium complex.
We
started to test with various rho-
dium catalysts [{RhCl
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(cod)} ],
2
[Rh
A
H
U
G
R
N
U
G
[Rh-
6
5
3
3
A
H
U
G
R
N
N
(cod) ]BF , and [{Rh
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(OMe)-
2
4
Scheme 1. Various CÀX bond formations by CÀCN cleavage.
AHCTUNGTRNENUG( cod)} ] in dioxane at 1208C.
2
Disappointingly, the results in-
dicated that the rhodium catalysts were completely ineffec-
tive in this reaction. After further screening of catalysts we
transferred to nickel catalysts, which are commonly used to
activate CÀCN bonds in different carbocyanation or cross-
respectively reported rhodium-catalyzed reductive decyana-
[7]
tion (Scheme 1, Path B) and silylation (Scheme 1, Path
[
8]
C); however, examples of metal-mediated CÀP bond for-
mation has yet to be reported. Although a manifold of
[5,6]
methods for the formation of CÀP bonds has been estab-
coupling reactions of aryl cyanides.
perimentation, we found that the use of [NiCl2
[NiCl2(PCy ) ] as a catalyst, tBuOK as the base and CuF as
After extensive ex-
lished, generally only highly reactive aryl halides (such as I
or Br) or triflates can be used as coupling partners or specif-
ic and expensive ligands are required to facilitate the high
ACHTUNGTRENNUNG
(PPh ) ] and
3
2
AHCTUNGTRENNUNG
3
2
2
the additive was critical for obtaining the desired aromatic
diphenylphosphine in 91 and 95% yields, respectively
[9]
reactivities. Inspired by these important studies of CÀCN
(
Table 1, entries 2 and 3). Encouraged by this result we
chose the more stable and cheap [NiCl (PPh ) ] as the cata-
AHCTUNGTRENNUNG
2
3 2
[
a] M. Sun, H.-Y. Zhang, Q. Han, K. Yang, Prof. S.-D. Yang
State Key Laboratory of Applied Organic Chemistry
Lanzhou University, Lanzhou 730000 (P.R. China)
Fax : (+86)931-8912859
lyst and evaluated a variety of bases and additives for their
potential in this transformation. The results indicated that
the base plays a crucial role in this reaction system; tBuONa
and CH ONa were also promising, affording 2a in 62 and
E-mail: yangshd@lzu.edu.cn
3
5
5% yields (Table 1, entries 4 and 6). Other bases such as
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201101930.
K PO , Cs CO were ineffective (Table 1, entries 5 and 7). A
3
4
2
3
9566
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 9566 – 9570