Menthyl-Substituted Group 4 Metallocene Dihalides

Menthyl-substituted group 4 metallocene dihalides of type Cp′2MX2 (Cp′ = η5-menthyl-C5H4) have been known so far for M = Ti, Zr, and X = Cl (1-Ti, 1-Zr). A gap in knowledge is closed now by the expansion to hafnium (1-Hf) and the preparation of complexes with X = F (4-Ti, 4-Zr, 4-Hf). In a first catalytic application 1-Ti is used in the enantioselective Buchwald hydrosilylation of imines and compared to (S,S)-(ebthi)TiF2. Also the variation of the ligand to (η5-8-phenylmenthyl-C5H4) is realized with a zirconocene dichloride (3-Zr). The reduction of 1-Ti afforded compound 2, a dimeric titanium(III) complex, [Cp′2Ti(μ-Cl)2TiCp′2]. Such a species is assumed to be an intermediate in the ring-opening reaction of epoxides with titanocene dichlorides as precatalysts.