Analysis of Stereochemistry Control in Homogeneous Olefin Polymerization Catalysis

We propose a new method, using statistical analysis, to quantify factors contributing to stereo- and regiocontrol in olefin polymerization catalysis and competing beta-hydrogen transfer to monomer. The method has been applied to three rather different Zr-based catalysts: (1) rac-Me2Si(3-Me-C5H3)(2)ZrR+, a representative of standard ansa metallocenes; (2) [2,2'-bis(2-indenyl)biphenyl]ZrR+, a sterically congested and rather atypical metallocene; and (3) [1,2-(2-O-3-tBu-C6H3CH2NMe)(2)-C2H4]ZrR+, an example of an octahedral ONNO-type catalyst. The analysis produces separate numeric values for repulsive ligandchain, chainmonomer, and ligandmonomer interactions. For insertion in the ZriBu bond of 1 and 3, the ordering is syn (similar to 2.3 kcal/mol) > ligandchain (similar to 1.6) > ligandmonomer (similar to 1.3), while for more crowded system 2 the three interactions are all around 2.02.5 kcal/mol. Despite the non-negligible magnitude of the ligandchain interaction, the standard Corradini model of stereocontrol was found to apply for all cases. Our results also indicate that the stereocontrol penalties are sensitive to the nature of the chain and the olefin and that extrapolation from H or Me chains to more realistic chains is not warranted.