MOLECULAR ORBITAL AND IMOMM STUDIES OF THE CHAIN TRANSFER MECHANISMS OF THE DIIMINE-M(II)-CATALYZED (M = NI, PD) ETHYLENE POLYMERIZATION REACTION

Associative displacement and H-exchange chain transfer/termination mechanisms for the diimine−M(II)-catalyzed (M = Ni, Pd) ethylene polymerization have been studied using B3LYP and IMOMM methods. For unsubstituted diimine complexes the coordination of ethylene to the metal−olefin−hydride complexes L2M(C2H4)H+ and L2M(C3H6)H+ is exothermic and gives the five-coordinate complex 22. From 22, the following processes can take place:  (a) the associative displacement, path E, corresponding to dissociation of propylene, (b) the dissociation of ethylene, reverse path D, (c) the H-exchange, path F, and (d) the reattaching of the hydrogen to the polymer chain, path G. For M = Ni, the associative displacement cannot compete with paths F and G and is unlikely to take place. For M = Pd, the energetics for the paths E−G are similar, and the chain transfer/termination via the associative dissociation path E is more likely. The H-exchange process, path F, is the most favorable chain transfer/termination mechanism for bot...