Platinum-catalyzed double silylations of alkynes with bis(dichlorosilyl)methanes

Abstract

Bis(dichlorosilyl)methanes 1 undergo the two kind reactions of a double hydrosilylation and a dehydrogenative double silylation with alkynes 2 such as acetylene and activated phenyl-substituted acetylenes in the presence of Speier’s catalyst to give 1,1,3,3-tetrachloro-1,3-disilacyclopentanes 3 and 1,1,3,3-tetrachloro-1,3-disilacyclopent-4-enes 4 as cyclic products, respectively, depending upon the molecular structures of both bis(dichlorosilyl)methanes ( 1) and alkynes ( 2). Simple bis(dichlorosilyl)methane ( 1a) reacted with alkynes [R 1–C C–R 2: R 1 = H, R 2 = H ( 2a), Ph ( 2b); R 1 = R 2 = Ph ( 2c)] at 80 °C to afford 1,1,3,3-tetrachloro-1,3-disilacyclopentanes 3 as the double hydrosilylation products in fair to good yields (33–84%). Among these reactions, the reaction with 2c gave a trans-4,5-diphenyl-1,1,3,3-tetrachloro-1,3-disilacyclopentane 3ac in the highest yield (84%). When a variety of bis(dichlorosilyl)(silyl)methanes [(Me n Cl 3 − n Si)CH(SiHCl 2) 2: n = 0 ( 1b), 1 ( 1c), 2 ( 1d), 3 ( 1e)] were applied in the reaction with alkyne ( 2c) under the same reaction conditions. The double hydrosilylation products, 2-silyl-1,1,3,3-tetrachloro-1,3-disilacyclopentanes ( 3), were obtained in fair to excellent yields (38–98%). The yields of compound 3 deceased as follows: n = 1 > 2 > 3 > 0. The reaction of alkynes ( 2a– c) with 1c under the same conditions gave one of two type products of 1,1,3,3-tetrachloro-1,3-disilacyclopentanes 3 and 1,1,3,3-tetrachloro-1,3-disilacyclopent-4-enes ( 4): simple alkyne 2a and terminal 2b gave the latter products 4ca and 4cb in 91% and 57% yields, respectively, while internal alkyne 2c afforded the former cyclic products 3cc with trans form between two phenyl groups at the 3- and 4-carbon atoms in 98% yield, respectively. Among platinum compounds such as Speier’s catalyst, PtCl 2(PEt 3) 2, Pt(PPh 3) 2(C 2H 4), Pt(PPh 3) 4, Pt[ViMeSiO] 4, and Pt/C, Speier’s catalyst was the best catalyst for such silylation reactions.