Pyridylamido hafnium complexes with a silylene bridge: synthesis and olefin polymerization

摘要

The synthesis and characterisation of six novel C-s-symmetric pyridylamido hafnium complexes with a silylene bridge of the type [ArPy(R2Si)NAr']HfAlk(2) are reported. Four complexes have been structurally characterised using single crystal X-ray diffraction. Appreciable differences between the solid state structures of these complexes and the pyridylamido hafnium complexes with a CRR' bridge were noted. Reactions with B(C6F5)(3), [Ph3C][B(C6F5)(4)] and [HMe2NPh][B(C6F5)(4)] yielded active catalysts for the homopolymerisations of propene and 1-hexene and ethene/1-octene copolymerization. In spite of the C-s-symmetry of the precatalysts, isotactically enriched polypropylene and poly(1-hexene) were obtained. The fact that the mechanism of the catalyst activation includes the insertion of alkene into the Hf-C-Ar bond was demonstrated. It was found that the structures of Ar and the R2Si bridge influence the activity, molecular weight capability and 1-octene affinity of the catalysts.