Non-π-Allyl Mechanism for the 1,4-cis-Butadiene Polymerization: Theoretical Study of Polymerization via Insertion of Butadiene into Al-C Bond with Cationic Gadolinium Metallocene.

This paper reports a computational study on the specific 1,4-cis polymerization of butadiene catalyzed by the cationic gadolinium metallocene [(C 5 Me 5 ) 2 Gd][B(C 6 F 5 ) 4 ] combined with excess amount of Al( i Bu) 3 . Because this reaction system has no initial Gd-alkyl bond, a mechanism with conventional coordinative chain transfer polymerization (CCTP) is not feasible. Density functional theory (DFT) analyses indicate a novel mechanism in which the cationic Gd plays a crucial role by assisting butadiene insertion into one of the Al-C bond of Al( i Bu) 3 . The proposed butadiene polymerization mechanism can account for the specific 1,4-cis selectivity of this catalyst system.