The influence of electronic and steric factors on chain branching in ethylene polymerization by Brookhart-type Ni(II) diimine catalysts: a combined density functional theory and molecular mechanics study

摘要

Calculations have been carried out on the energy of ethylene complexation to the metal center in the Brookhart-type Ni(II) diimine olefin polymerization catalyst (ArN=C(R)-C(R)=NAr)Ni(II)CH_3~+ for C(R)-C(R)=CH-CH; C(Me)-C(Me) and C-ANAP-C (ANAP = acenaphthalene). The goal of this study was to examine the influence of the C(R)-C(R) substitution on the chain branching in the Brookhart Ni(II) diimine olefin polymerization catalysts. Experimental results suggest that the branching rates are controlled by the equilibrium between the #pi#-complex and the metal alkyl. The branching rates were found experimentally to follow the trend R=H < ANAP < CH_3. It is shown that the trend in branching can be explained by the calculated order of olefin complexation R=H > ANAP > CH_3. It is further shown that the order of complexation energy is influenced by both electronic and steric factors.