Novel unsymmetrical ansa-metallocenes Me(2)C(3-t-Bu-C5H3)(3-R-C9H5)MCl(2) (R = t-Bu; M = Ti (1a), M = Zr (1b), M = Hf(1c)), Me(2)Si(3-t-Bu-C5H3)(3-t-Bu-C9H5)ZrCl2 (2), and Me(2)C(3-t-Bu-C5H3)(3-Me-C9H5)ZrCl2 (3) were synthesized and separated into three and erythro isomers by repeated recrystallization. The molecular structure of Me(2)C(3-t-BuC(5)H(3))(3-t-Bu-C9H5)ZrCl2 (threo-1b) was determined by X-ray crystallography. Polymerization of propylene with one of these metallocene complexes (threo-1b) coupled with MAO (methylaluminoxane) in toluene was found to afford a highly isotactic polymer of M(w) 105 000 with % mm > 99.6 which shows an extremely high melting point of 161 degrees C.