Silicon–Carbon bond cleavage reactions of Ansa tungstenocene compounds: The [Me2Si] bridge as a site for metallocene functionalization

[Me2Si(CpMe2)2]W(H)Cl is obtained via reaction of WCl6 with a mixture of [Me2Si(CpMe2)2]Li2 and NaBH4, from which the dichloride [Me2Si(CpMe2)2]WCl2 is obtained via treatment with CHCl3. [Me2Si(CpMe2)2]WCl2 provides a means to access other ansa tungstenocene compounds, such as [Me2Si(CpMe2)2]WH2, [Me2Si(CpMe2)2]WMe2, and [Me2Si(CpMe2)2]WCO. Of most interest, the reactions of [Me2Si(CpMe2)2]W(H)Cl with organolithium reagents do not yield simple ansa tungstenocene derivatives. Specifically, the reactions of [Me2Si(CpMe2)2]W(H)Cl with MeLi, BunLi, or PhLi result in the formation of mixed-ring tungstenocene compounds resulting from C–Si cleavage and functionalization of the ansa bridge, namely (CpMe2)(η5,κ1–C5H2Me2SiMe2CH2)WH, (CpMe2)[η5,κ1–C5H2Me2Si(Me)(Bun)CH2]WH, and (CpMe2)[η5,κ1–C5H2Me2SiMe2(C6H4)]WH, respectively. In contrast to the C–Si cleavage achieved by MeLi, BunLi, and PhLi, the ansa bridge of [Me2Si(CpMe2)2]W(H)Cl is inert to ButLi and the product obtained is the fulvene (“tuck-in”) complex [Me2Si(CpMe2)(η6–C5MeH2CH2)]WH derived from dehydrohalogenation.