Copolymerization of Ethylene with Polar Monomers: Chain Propagation and Side Reactions. A DFT Theoretical Study Using Zwitterionic Ni(II) and Pd(II) Catalysts

Calculations utilizing anionic substituted derivates of the cationic N∧N Ni(II) and Pd(II) diimine Brookhart complex have been carried out on the barriers of ethylene and acrylonitrile insertion into a M− methyl, propyl and CH(CN)Et bond for M = Ni, Pd. The possibility of side reactions such as chelate formation with the polar functionality and oligomerization of the active species after acrylonitrile insertion are explored. The diimine ring system N∧N = −NR‘ ‘CR1CR2NR‘ ‘ with R‘ ‘ = 2,6-C6H3(i-Pr)2 and R1,R2 = Me was functionalized by adding one or two anionic groups (BF3-, etc.) in place of i-Pr on the aryl rings or by replacing one Me diimine backbone group (R1) with BH3-. The objective of this investigation is computationally to design catalysts for ethylene/acrylonitrile copolymerization that have activities that are comparable to that of the cationic Ni(II) diimine or at least the Pd(II) diimine Brookhart system for ethylene homopolymerization. Complexes that might meet this objective are discussed.