A Theoretical Outlook on the Stereoselectivity Origins of Isoselective Zirconocene Propylene Polymerization Catalysts

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Abstract
The first three insertion steps of propylene for isoselective metallocenes from the {Cp/Flu}‐ and {SBI}‐families were computed using a theoretical method implementing the B3PW91 functional in combination with solvent corrections incorporated with the SMD continuum model. For the C1‐symmetric {Cp/Flu}‐type metallocenes, two mechanisms of stereocontrol were validated theoretically: more facile and more stereoselective chain "stationary" insertion (or site epimerization back‐skip) and less stereoselective alternating mechanisms. For the C2‐symmetric {SBI}‐type system, computation results are in complete agreement with the sole operating chain migratory insertion mechanism. The thermochemical data obtained through the study were used to predict microstructures of polypropylenes using three‐parameter and one‐parameter statistical models for the two metallocene systems, respectively. The calculated meso/rac pentad distributions were found in good agreement with those determined experimentally for iPP samples obtained at different polymerization temperatures.

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