Reactions of Group 4 Metallocenes with Monosubstituted Acetonitriles: Keteniminate Formation versus C-C Coupling

The reactions of the Group 4 metallocene dichlorides [Cp-2'MCl2] (1a: M=Ti, Cp'=Cp*=eta(5)-pentamethylcyclopentadienyl, 1b: M=Zr, Cp'=Cp=eta(5)-cyclopentadienyl) with lithiated MesCH(2)-C N gave [Cp-2*TiCl(N=C=C(HMes))] (3; Mes=mesityl) in the case of 1a. For compound 1b, a nitrile-nitrile coupling resulted in a five-membered bridge in 4. The reaction of the metallocene alkyne complex [Cp-2*Zr(eta(2)-Me3SiC2SiMe3)] ( 2) with PhCH2-C N led in the first step to the unstable product [Cp-2*Zr(eta(2)-Me3SiC2SiMe3)(NC-CH2Ph)] (5). After the elimination of the alkyne, a mixture of products was formed. By variation of the solvent and the reaction temperature, three compounds were isolated: a diazadiene complex 6, a bis(keteniminate) complex 7, and 8 with a keteniminate ligand and a five-membered metallacycle. Subsequent variation of the Cp ligand and the metal center by using [Cp2Zr] and [Cp-2*Ti] with Me3SiC2SiMe3 in the reactions with PhCH2-C N gave complex mixtures.