Pure Appl. Chem., 2008, Vol. 80, No. 5, pp. 1179-1185
doi:10.1351/pac200880051179
Cationic palladium-catalyzed hydrosilylative cross-coupling of alkynes with alkenes forming 4-silylated-1-butene frameworks*
Takamitsu Shimamoto, Motoharu Chimori, Hiroaki Sogawa, Yuki Harada, Masaharu Aoki, and Keiji Yamamoto
Department of Materials Science and Environmental Engineering, Tokyo University of Science, Yamaguchi, 1-1-1 Daigaku-Dori, Sanyo-Onoda, Yamaguchi 756-0884, Japan
Abstract:
A new hydrosilylative cross-coupling reaction of a variety of alkynes with several alkenes, which is catalyzed by a cationic Pd complex [Pd(η3-C3H5)(cod)]+[PF6]- (cod = 1,5-cyclooctadiene) was studied systematically. The reaction using HSiCl3 as an addend afforded more or less two types of products consisting of four possible derivatives, R1CH=CR2-CHR3-CHR4-SiCl3, which always contained 4-trichlorosilyl-1-butene frameworks, in acceptable combined yields. The coupling pattern was markedly dependent both on the precatalyst in the absence or presence of PPh3 ligand and on the combination of the alkyne and alkene partners employed. A possible catalytic cycle that involves an initial hydropalladation of an alkyne, followed by a facile and specific carbopalladation of an alkene, is proposed. At the same time, the lack of regioselectivity in the latter step is noted.
Keywords: alkenes; alkynes; carbopalladation; cationic palladium complex; cross-coupling; hydropalladation; hydrosilanes.
*Paper based on a presentation at the 14th International Symposium on Organometallic Chemistry Directed Towards Organic Synthesis (OMCOS-14), 2-6 August 2007, Nara, Japan. Other presentations are published in this issue, pp. 807-1194.