Mono- and Dinuclear Cyclopentadienylsiloxo Titanium Complexes: Synthesis, Reactivity, and Catalytic Polymerization Applications

Abstract

Hydrolysis of the (dichloromethylsilyl)cyclopentadienyl titanium compound [Ti(η5-C5Me4SiMeCl2)Cl3] gave the metallasiloxane dinuclear complex [(TiCl2)2(μ-{(η5-C5Me4SiMeO)2(μ-O)})] (1a). Addition of 4 equiv of RMgCl (R = Me, Bz) to 1a afforded the corresponding tetraalkyl dititanium derivatives [(TiR2)2(μ-{(η5-C5Me4SiMeO)2(μ-O)})] (R = Me 1b, Bz 1c). The benzyl compound 1c reacted with E(C6F5)3 (E = B, Al) and [Ph3C][B(C6F5)4] to give the bridged dititanium compounds [(TiBz)2(μ-{(η5-C5Me4SiMeO)2(μ-O)})(μ-X)][Q] (Q = BzB(C6F5)3; X = Br, 2Br; Cl, 2Cl; F, 2F; Q = BzAl(C6F5)3; X = Cl, 3Cl; Q = B(C6F5)4; X = Bz, 4Bz; Cl, 4Cl) by benzyl abstraction and further reaction with the corresponding halogenated solvents. The addition of excess B(C6F5)3 to 1c gave the bis(zwitterionic) benzyl intermediate [(TiBz{η6-PhCH2B(C6F5)3})2(μ-{(η5-C5Me4SiMeO)2(μ-O)})] (6), which evolved into the bis(zwitterionic) fulvene derivative [(Ti{η6-PhCH2B(C6F5)3})2(μ-{(η5-C5Me3(η1-CH2)SiMeO)2(μ-O)})] (5). Related mononuclear siloxo compounds [TiCp*R2(OSiiPr3)] (Cp* = η5-C5Me5; R = Cl, 7a; Me, 7b) were obtained from the reaction of [TiCp*R3] (R = Cl, Me) with HOSiiPr3. Compound 7b reacted with E(C6F5)3 (E = B, Al) in C6D6, affording the thermally stable ion-paired derivatives [TiCp*Me(OSiiPr3){MeE(C6F5)3}] (E = B, 8B; Al, 8Al). The chloro dinuclear 1a and mononuclear 7a complexes were tested as ethylene polymerization catalysts and the alkyl complexes 1b, 1c, and 7b as methylmethacrylate polymerization catalysts