Borabenzene Derivatives. 26.1 Syntheses of 1-Methylboratabenzene Complexes of Titanium, Zirconium, and Hafnium. Structures of TiCl3(C5H5BMe), TiCl2Cp(C5H5BMe), ZrCl2(C5H5BMe)2, and ZrCl2Cp*(C5H5BMe)

The complexes TiCl 3 (C 5 H 5 BMe) ( 6a ), [MCl 3 (C 5 H 5 BMe)] x ( 6b, M = Zr; 6c, M = Hf), and MCl 2 (C 5 H 5 BMe) 2 ( 7b, M = Zr; 7c, M = Hf) are obtained from the tetrachlorides MCl 4 (M = Ti, Zr, Hf) and Li(C 5 H 5 BMe) ( 3 ), 2-(Me 3 Si)C 5 H 5 BMe ( 4 ), or 2-(Me 3 Sn)C 5 H 5 BMe ( 5 ) in excellent yields. The complexes MCl 2 Cp(C 5 H 5 BMe) ( 8a, M = Ti; 8b, M = Zr) and MCl 2 Cp*(C 5 H 5 BMe) ( 9b, M = Zr; 9c, M = Hf) are made similarly from the corresponding cyclopentadienyl precursors MCl 3 Cp (M = Ti, Zr) and MCl 3 Cp* (M = Zr, Hf). The redox potentials are shifted by 0.35−0.41 V to more anodic values than those for the corresponding Cp complexes. Molecule 6a shows a piano-stool-type structure, while 7b, 8a, and 9b possess typical bent sandwich structures.