Synthesis, Structural Analysis, and Polymerization Activity of Noncyclopentadienyl Constrained Geometry Complex [Me2Si(Ph2C)(tBuN)]ZrCl2(thf)

Abstract

Constrained geometry complexes (CGCs) are homogeneous olefin polymerization catalysts that have been improved because of their considerably high activity and their copolymerization abilities for ethylene with α-olefins. The ancillary ligands in CGCs comprise bridged 6π-electron moieties (e.g., cyclopentadienyl (Cp) and fluorenyl) and amide donors. In this study, we investigated the effect of changing the 6π-electron moieties to a diphenylmethyl moiety (Ph₂C) on the polymerization activity of [Me₂Si(Ph₂C)(^tBuN)]ZrCl₂(thf) (thf = tetrahydrofuran). We synthesized [Me₂Si(Ph₂C)(^tBuN)]ZrCl₂(thf) and characterized it via ¹H nuclear magnetic resonance analysis and single-crystal X-ray crystallography. Ethylene polymerization at 2 MPa using a catalyst of the [Me₂Si(Ph₂C)(^tBuN)]ZrCl₂(thf) and modified methylaluminoxane (MMAO) as a cocatalyst yielded a linear polyethylene (PE) with a high melting point (124°C–134°C); moreover, the polymerization activity of the catalyst was found to be up to 445 g (PE) mmol (Zr)⁻¹ h⁻¹. The polymerization of styrene using the zirconium complex and MAOs did not proceed, but the polymerization of 1,3-butadiene produced a small amount of polybutadiene with ~60% cis-1,4-structure. These results indicate that non-Cp-type CGCs, which can be defined as metal complexes bearing an ancillary ligand in which non-Cp moieties (benzyl moiety in this study) and an amido group are bridged by an organic linker, can become a new family of homogeneous olefin polymerization catalysts.