Cp[Tm ^Me]ZrCl ₂, a tris(2-mercapto-1-methylimidazolyl) hydroborato complex of zirconium and a new type of precatalyst for olefin polymerization

Cp[Tm ^Me]ZrCl ₂, the first tris(2-mercapto-1- methylimidazolyl)hydroborato complex of zirconium, is obtained by reaction of CpZrCl ₃ with [Tm ^Me]K. The molecular structure of Cp[Tm ^Me]ZrCl ₂ has been determined by X-ray diffraction, and the geometry closely resembles the bent-metallocene motif of Cp ₂ZrCl ₂. An important distinction, however, is that Cp[Tm ^Me]-ZrCl ₂ is chiral, with C ₁ symmetry. The chirality of Cp[Tm ^Me]-ZrCl ₂ is a consequence of the fact that the [Tm ^Me] ligand exhibits a propeller-like twist such that it has local C ₃ symmetry and is therefore devoid of a mirror plane. Variable-temperature ¹H NMR studies demonstrate that enantiomer interconversion does not occur on the NMR time scale. In combination with methylalumoxane, Cp[Tm ^Me]ZrCl ₂ produces an active catalyst for ethylene polymerization.