Figure 1.

Relationship between the strain of the active chromium sites and reactivity, as determined by the computational work in ref (103). (a) Simplified illustration of the four-, six-, and eight-membered chromasiloxane ring (4CR, 6CR, and 8CR, respectively) models bearing Cr(II) species, with a qualitative indication of their relative abundance and strain, and the correlation with the Cr–O distance and O–Cr–O angle. By moving from yellow to red, the strain increases. (b) Most relevant energetic values as extrapolated from the Gibbs free energy profiles for ethylene binding on Cr(II) and for ethylene insertion and β-hydrogen transfer on the corresponding Cr(III)-ethyl models. (c) Predicted average MW of the PE obtained from the three models, determined by the kinetic competition between chain propagation and chain transfer. Data reproduced with permission from ref (103). Copyright 2022 American Chemical Society.