A set of 19 silicon-bridged C 2 -symmetric zirconocenes rac-R′ 2 Si(2-Me-4-R-indenyl) 2 ZrCl 2 of varying steric demand in position 4 were synthesized and screened in propene homopolymerization in a high-throughput experimental setup. The size and accuracy of the experimental data set allow to identify surprisingly good correlations among stereoselectivity, regioselectivity, and molecular weight capability (R 2 ≈ 0.8−0.9) over a broad range. We rationalize this trend by assuming that steric tuning in the 4-position affects both preferred insertion and stereoerror formation similarly but leaves other barriers largely unaffected. A quantitative structure−activity relationship based on one single computational descriptor, Δ%V Bur using the difference in the percent of buried volume between the "blocked" and "open" quadrants of the catalyst precursoris established. Provided that a large sphere of 5.0 Å is used, stereoselectivity can be predicted with unprecedented accuracy, i.e., a mean average deviation (MAD) of 0.18 kcal/mol (ΔΔG ‡ enantio ), 0.0007 (σ, probability that the preferred propene enantioface is selected at an active site of given chirality), or 0.3% (mmmm pentads). On the basis of this empirical model, we predicted that the catalyst with R = o-tolyl is an ideal candidate for high stereoselectivity/high MW capability. Ad hoc synthesis and testing of the precursor confirmed the expectations: the catalyst shows the highest stereoselectivity reported so far (σ = 0.9999) for metallocenes at 60 °C, while maintaining a high MW capability (M w > 1 MDa) and relatively high regioselectivity.

Absolute rigidity is rare in the “soft” world of organometallics. Here we introduce two cyclopenta­[a]­triptycyl ansa-zirconocene catalysts for isotactic-selective propene polymerization, designed by means of an integrated high-throughput experimentation/quantitative structure–activity relationship modeling approach. An ultrarigid ligand precisely wrapped around the Zr center enforces an enzyme-like lock and key fit, effectively hampering undesired reactive events, even at high temperature. Stereodefective units are hardly detectable by 13C NMR in the polymer produced at 120 °C; this corresponds to an enantioselectivity exceeding 6–7 kcal/mol: i.e., less than 1 propene misinsertion every 4000 (and at room temperature, one every ∼40000!).

Highly accurate high-throughput experimentation (HTE) data for a set of 21 silicon-bridged C 2-symmetric ansa-zirconocenes in propene homopolymerization were collected and were used to develop quantitative structure – activity relationship (QSAR) models for several performance indicators at high polymerization temperature (T p = 100 °C) by using chemically meaningful descriptors. Most notably, stereoselectivity is well described by a two-descriptor model linking the quadrant model for stereoselectivity (sterics) with the chain epimerization model (electronics). The catalysts show widely varying temperature responses, most notably on stereoselectivity and molar mass capability, while the regioselectivity response is uniformly weak. Soft conformational locks lose their performance rapidly while hard conformational locks offer enhanced performance even at high temperatures. The quest for high-temperature stable, well-performing ansa-zirconocenes will unquestionably lead to systems with enhanced rigidity.