Oligomerization and regioselective hydrosilylation of styrenes catalyzed by cationic allyl nickel complexes bearing allylphosphine ligands

Abstract

The complexes [Ni(η³-CH₂CHCH₂)Br(κ¹P-PR₂CH₂CHCH₂)] (R = Ph 1, ⁱPr 2) and [Ni(η³-CH₂C(R′)CH₂)(κ¹P-PR₂CH₂CHCH₂)₂][BAr′₄] (R′ = H, R = Ph 4a, R = ⁱPr 4b; R′ = CH₃, R = Ph 5a, R = ⁱPr 5b; Ar′ = 3,5-C₆H₃(CF₃)₂) have been prepared and characterized. The X-ray crystal structures of 1, 2 and 5b have been determined. 4a–b and 5a–b are catalyst precursors for the oligomerization of RC₆H₄CHCH₂ to oligostyrene (R = H) or oligo(4-methylstyrene) (R = CH₃) respectively, without the need of a co-catalyst such as methylalumoxane. The catalytic activities range from moderate to high. The oligomerization reactions are carried out in the temperature interval 25–40 °C in 1,2-dichloroethane, using an olefin/catalyst ratio equal to 200, yielding oligostyrenes with a high isotactic fraction content P_m, with M_n in the range 700–1900 Dalton, and polydispersities between 1.22 and 1.64. The cationic complexes 4a–b and 5a–b are also effective catalyst precursors for the hydrosilylation reactions of styrene or 4-methylstyrene with PhSiH₃ in 1,2-dichloroethane at 40 °C using an olefin/catalyst ratio equal to 100, leading selectively to RC₆H₄CH(SiH₂Ph)CH₃ (R = H, CH₃) in 50–79% yield.