Investigating Single Site Olefin Polymerization using a Quantum Mechanical/Molecular Mechanical (QM/MM) Model for the Counterion, B(C6F5)3CH3- : the Propagation Step

Kumar Vanka, Zhitao Xu and Tom Ziegler

Department of Chemistry, University of Calgary, Calgary, Alberta, Canada T2N 1N4
 

Density functional theory has been used to study the insertion of the ethylene monomer into the metal-propyl bond of different ionpair systems of the type L1L2MPr-m-MeB(C6F5)3 (M = Ti, Zr; Pr = C3H7; L1, L2 = C5H5, NC{C(CH3)3}2). This process is the second insertion of the monomer (ethylene) into the metal-alkyl bond ­ the propagation step. The counterion used in the studies, viz. MeB(C6F5)3-, has been modeled with a validated QM/MM model. Different conformations of the ionpair system have been considered. The influence of the counterion on the insertion process has been discussed, along with the effect of changing the metal centre. Different modes of approach of the ethylene monomer, cis and trans to the m-methyl bridge, have been discussed. Also discussed are solvent effects, incorporated with single point calculations done with cyclohexane as the solvent (e = 2.023).