Study of Cationic Palladium Complex-Catalyzed Cyclization-Hydrosilylation of α,ω-Diynes

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1)Taking advantage of the findings involving the palladium-catalyzed dimerization-hydrosilylalon of l-alkynes with trichlorosilane, we have developed a cationic palladium complex, which exhibits a specific catalytic activity for an intramolecular dimerization-hydrosilylation, i.e., cyclization-hydrosilylation of α,ω-alkadiynes. Thus, we have prepared 5, 6-membered (or even 7-membered) (Z)-1-(trichlosilyl)methylene-2-mthylenecycloalkanes starting from 1,6-heptadiyne derivatives and their homologs using typically trichlorosilane as an added.In order to elucidate a possible catalytic cycle of this unique reaction, the cyclization-hydrosilylation of unsymmetrical 1,6-octadiyne was carried out to give exclusively, (Z)-1(1'-trichlorosityl)ethylidene -2-methylenecyclopentane. The results well implicate that the hydropalladation takes place at a terminal alkyne site giving a vinylidene-palladium species, the latter, in turn, undergoing the carbopalladation with an internal alkyne site to cycli … More ze, followed by substitution with the hydrosilane to form the observed product and regenerate most probably a hydridopalladium as an acive catalyst. It is worthy of note that HSiMe_nCl_(3n) (n = 0 - 2) are equally applicable to this catalytic cylization-hydroilylation, while this is not the case for the dimerization-hydrosilylation of 1-alkynes mentioned above.2)Truly unexpected reaction product has been obtained when 9-oxa-1-dodecen-6,11-diyne was used as a substrate in the cationic palladium complex-catalyzed cyclization-hydrosilylation using trichlorosilane as an added. The major product (75%) identified was the one arising from the cyclization between an internal alkyne site and a terminal alkene, whereas the minor product (25%) was obtained from the ordinary intramolecular diyne cyclization. Furthermore, we have experienced that α,ω-alkenynes undergo the present cyclization-hydrosilylation generally much faster than the corresponding α,ω-alkadiynes.The results may suggest that, in the above mentioned catalytic cycle, the tale of carbopalladation at the alkene site must clearly be enhanced than that at the alkyne site. Thus, it is logically suggested to conduct any hydrosilylative cross-coupling of alkynes with alkenes. Less