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

Calculations have been carried out on the energy of ethylene complexation t o the metal center in the Brookhart-type Ni(II) diimine olefin polymerizati on catalyst (ArN = C(R)-C(R) = NAr)Ni(II)-CH3+ 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. Experiment al results suggest that the branching rates are controlled by the equilibri um between the pi-complex and the metal alkyl. The branching rates were fou nd experimentally to follow the trend R = H < ANAP < CH3. It is shown that the trend in branching can be explained by the calculated order of olefin c omplexation R = H > ANAP > CH3. It is further shown that the order of compl exation energy is influenced by both electronic and steric factors. (C) 199 9 Elsevier Science S.A. All rights reserved.