STEREOREGULAR POLYMERIZATION OF ALPHA-OLEFINS CATALYZED BY CHIRAL GROUP-4 BENZAMIDINATE COMPLEXES OF C-1 AND C-3 SYMMETRY

The chiral lithium (-)-trimethylsilylmyrtanyl amide reacts with benzon itrile yielding the chiral benzamidinate lithium ligand ([N-trimethyls ilyl] [N'-myrtanyl]benzamidinate Li.TMEDA (TMEDA = tetramethylethylene diamine), [N(R)-C - N] Li. An X-ray study shows that the ligand has a distorted tetrahedral environment in which the lithium atom is arrang ed symmetrically between the two benzamidinate and the two TMEDA nitro gen 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 oc tahedral structure with the oxygen atom and one chlorine atom at the a pical 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 trimethy lsilyl groups in a cis position with respect to the chlorine atom and the other three myrtanyl groups arranged on the opposite side of the c hlorine. 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 stru cture 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 propy lene producing elastomeric polypropylene and for the syndiotactic poly merization of styrene. Complex 2 was found to be active for the highly stereospecific polymerization of propylene.