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Tetrahedron 64 (2008) 3655e3660
Palladium bis(2,2,6,6-tetramethyl-3,5-heptanedionate) catalyzed
Suzuki, Heck, Sonogashira, and cyanation reactions
*
Nitin S. Nandurkar, Bhalchandra M. Bhanage
Department of Chemistry, Institute of Chemical Technology (Autonomous), University of Mumbai, N. Parekh Marg, Matunga, Mumbai-400019, India
Received 31 December 2007; received in revised form 12 February 2008; accepted 13 February 2008
Available online 16 February 2008
Abstract
Palladium bis(2,2,6,6-tetramethyl-3,5-heptanedionate): a structurally well-defined O-containing transition metal complex is reported as an
efficient catalyst for Suzuki, Heck, and Sonogashira cross-coupling reactions. The protocol was also applied successfully for cyanation of
aryl halides under milder operating conditions. The system tolerated the coupling of various aryl halides with alkenes, alkynes, and organobor-
onic acid along with the cyanation of aryl halides providing good to excellent yields of desired products.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Suzuki reaction; Heck reaction; Sonogashira reaction; Cyanation reaction; TMHDepalladium complex
1. Introduction
Pd-NHC,8 [C3CNpy]2[PdCl4],9 etc. for Suzuki reacion; (b) Pd/
DPPP [DPPP¼1,3-bis(diphenyl phosphinopropane)],10 Pd-
TXPTS [TXPTS¼tris(4,6-dimethyl-3-sulfonatophenyl) phos-
phine],11 Pd/C-Aliquot,12 Pd(OAc)2/[bmim]PF6,13 etc. for
Heck reaction; and (c) Pd(OAc)2/DABCO,14 Cyclopalladated
ferrocenyl imines,15 PdCl2(PPh3),16 PdCl2/pyrolidine,17
MCM-41-S-Pd(O),18 etc. for Sonogashira cross-coupling reac-
tion. The reaction system mostly employs an in situ generated
catalyst from a Pd source and highly efficient N/P containing
ligand. Inspite of the significant advances in this area, very few
reports employ a structurally well-defined Pd complex as a cat-
alyst.19 Thus, there is a need to develop a chemically well-de-
fined, air stable single-component Pd complex as a versatile
catalyst for Suzuki, Heck, Sonogashira, and cyanation reac-
tions. Previously, we reported C- and N-arylation of heterocy-
cles and carbonylative Sonogashira coupling reaction using
a preformed Pd and Cu bis(2,2,6,6-tetramethyl-3,5-heptanedi-
onate) as the catalyst.20 The use of 2,2,6,6-tetramethyl-3,5-
heptanedione (TMHD) as a ligand resulted in excellent yields
of products and such reactivity could be attributed to the fact
that a good balance exists between the steric and electronic
properties of the complex.
Homogenous catalysts offer some important advantages
over their heterogeneous counterparts.1,2 Such catalysts can
usually be dissolved in reaction media making all catalytic
sites accessible to reactants in solution. In addition many ho-
mogenous catalysts demonstrate high selectivity and can be
utilized to control the stereochemistry and regiochemistry of
the reaction products. Because of these advantages the forma-
tion of carbonecarbon bonds via homogenous palladium cat-
alyzed cross-coupling reactions has become an essential tool
for synthetic organic chemists. In CeC bond formation reac-
tions particular attention has been paid to the coupling of
aryl halides with organoboronic acids (Suzuki cross-coupling
reaction),3 alkenes (Heck reaction),4 and alkynes (Sonogashira
cross-coupling reaction),5 respectively. These Pd-catalyzed
cross-coupling reactions are ranked today among the most
general transformations in organic synthesis, which have great
industrial potential for the synthesis of chemicals, therapeutic
drugs, and their intermediates. Several groups have extended
these methodologies for coupling of aryl halides employ-
ing catalyst such as (a) (AdNC)2PdCl2,6 Pd(OAc)2/TBAB,7
Herein, we report a facile Suzuki, Heck, Sonogashira, and
cyanation reactions catalyzed by a well-defined O-containing
transition metal complex, via Pd bis(2,2,6,6-tetramethyl-3,5-
* Corresponding author. Tel.:þ91 2224145616; fax: þ91 2224145614.
0040-4020/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.02.038