Mechanistic Insights into Isotactic 1-Butene Polymerization: Accessing Novel Microstructures with Nonmetallocene Pyridylamido-Hf Catalysts

The polymerization of 1-butene using a C2-symmetric ansa-metallocene and a nonmetallocene pyridylamido-Hf catalyst was investigated through a combined experimental and theoretical approach. Density functional theory (DFT) calculations were employed to analyze key mechanistic aspects, including stereoselectivity, regioselectivity, chain termination, and isomerization pathways. The computational results reveal pronounced differences in the number-average molecular masses (Mn) and microstructures produced by the two catalyst classes. The ansa-metallocene is predicted to generate low Mn isotactic poly(1-butene) (iPB) characterized by classical 4,1-units arising from isomerization of regioirregular 2,1-units. In contrast, the nonmetallocene complex exhibits strong potential for producing higher Mn iPB with an unprecedented microstructure. Specifically, the DFT study suggests the formation of a microstructure featuring in-chain 2,1- and 3,1-units, which have not been reported previously. These theoretical outcomes were confirmed experimentally through the synthesis of iPB samples and their microstructural characterization by 13C NMR spectroscopy.