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 TiCl 4 in THF yields [N(R*)−C−N]TiCl 3 ·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) Å. 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.