Aminosilylene-bridged ansa-zirconocenes for branched polyethylenes with bimodal molecular weight distributions

Reactions of the dilithium salt of aminosilylene-bridged ligands with (Me2N)2ZrCl2(THF)2 followed by the treatment of Me3SiCl are found to be an efficient synthetic route to aminosilylene-bridged ansa-zirconocenes, R2N(Me)Si(η5–C5H4)2ZrCl2 (R = Me (1), Et (2)) and Me2N(Me)Si(η5–C5H4)(η5–C5Me4)ZrCl2 (3). Crystal structure of 3 determined by X-ray diffraction study reveals the presence of π-bonding interaction between N and Si atoms, which is further supported by DFT calculation results. These complexes are very active (>1 × 103 Kg/(mol Cat.·atm·h)) for homopolymerization of ethylene in the presence of methylalumoxane (MAO) cocatalyst, generating polyethylenes that contain branches as well as bimodal molecular weight distribution (MWD). Methyl, ethyl, butyl, and other longer branches (n ≥ 6) are observed in the resulting polyethylenes. The polyethylenes from 1, 2 and 3/MAO show a broad MWD range (6.3–42.2, 3.5–4.0 and 2.6–3.4, respectively).