Unexpected Selective Methyl Group Abstractions from SiMe3 Moieties of CH2SiMe3 Ligands To Give New Cationic Titanium Complexes

The synthesis of the alkylated pentafulvene titanium complex Cp*Ti(CH2SiMe3)(π-η5:σ-η1-C5H4=CR2) (CR2=adamantylidene) is described. The coordination mode of the pentafulvene ligand in this complex allowed for the subsequent synthesis of a series of nitrile-insertion products. By reacting these neutral compounds with the strong Lewis acid B(C6F5)3, unprecedented selective methyl-group abstractions from the SiMe3 moieties under formation of novel cationic titanium complexes with the corresponding MeB(C6F5)3− anion are demonstrated. The proposed silylium ion intermediates of these reactions are directly stabilized by either the exocyclic carbon atom of the pentafulvene ligand or by the lone pairs of the nitrogen atoms of the chelating Cp,N-ligands. In addition, a titanium enamine complex and its reaction with B(C6F5)3 is reported, which results in the formation of a betaine.