Stereoregular polymerization of α-olefins catalyzed by chiral group 4 benzamidinate complexes of C1 and C3 symmetry

The chiral lithium (-)-trimethylsilylmyrtanyl amide reacts with benzonitrile yielding the chiral benzamidinate lithium ligand ([N-trimethylsilyl] [N'-myrtanyl]benzamidinate Li.TMEDA (TMEDA = tetramethylethylenediamine), [N(R*)-C - N] Li. An X-ray study shows that the ligand has a distorted tetrahedral environment in which the lithium atom is arranged symmetrically between the two benzamidinate and the two TMEDA nitrogen atoms. Equimolar addition of [N(R*)-C-N]Li to TiCl4 in THF yields [N(R*)-C-N]TiCl3 .THF (1). An X-ray study of 1 shows that it has an octahedral structure with the oxygen atom and one chlorine atom at the apical positions. [N(R*)-C-N](3)ZrCl . toluene (2) can be prepared in a manner related to that employed to synthesize 1. An X-ray study of 2 shows that it has a capped octahedral geometry with the three trimethylsilyl groups in a cis position with respect to the chlorine atom and the other three myrtanyl groups arranged on the opposite side of the chlorine. Addition of MeLi . LiBr to complex 2 yields [N(R*)C-N](3)ZrMe (3) which is obtained as cocrystalline with complex 2. The X-ray structure of the cocrystalline mixture is similar to that of the chloride complex 2 exhibiting a Zr-Me distance of 2:469(10)Angstrom. Complex 1 is an active catalyst, under pressure, for the polymerization of propylene producing elastomeric polypropylene and for the syndiotactic polymerization of styrene. Complex 2 was found to be active for the highly stereospecific polymerization of propylene.