New Nickel(II) Diimine Complexes and the Control of Polyethylene Microstructure by Catalyst Design

Starting from differently substituted boronic acids as versatile building block, new “ortho-aryl”
α-diimine ligands a−h were synthesized in an easy, high-yielding route. Reaction of the complex precursor
diacetylacetonato-nickel(II) with a trityl salt, like [CPh3] [B(C6F5)4] or [CPh3] [SbCl6], in the presence of the
diimine ligands afford the monocationic, square planar complexes 2a−g in almost quantitative yields. Suitable
crystals (2d‘,e,f,g) were submitted for X-ray diffraction analysis. A geometry model was developed to describe
the orientation of ligand fragments around the nickel(II) center that influence the polymer microstructure.
At elevated reaction temperature and pressure, and in the presence of hydrogen, 2a−e catalyze the
homopolymerization of ethylene to give branched PE products ranging from HD- to LLD-PE grades. The
polymerization results indicate the possibility of precise microstructure control depending on the particular
complex substitution. Preliminary investigations on material density and mechanical behavior by uniaxial
stretching until failure point toward new material properties that can result from the simple ethylene monomer
by catalyst design.