Manipulating pre-equilibria in olefin polymerization catalysis: backbone-stiffening converts a living into a highly active salan-type catalyst

Stiffening of the catalyst backbone of salan-type catalyst 1via ring closure yields indanosalan 3 and increases activity and molar mass capability by two orders of magnitude. In propene polymerization, catalyst 3 is highly isotactic selective and nearly as active as one of the most productive known salan-catalysts today (2), showing much higher molar mass capability. NMR studies provide evidence of the identity of the active metal-polymeryl species for the catalyst pair 1/3, explaining their vast activity differences: the traditional salan catalyst 1 is trapped in the inactive mer-mer configuration, while indanosalan 3 prefers the active fac-fac isomer. Stiffening the catalyst backbone of a slow salan-type catalyst converts it into a highly active indanosalan catalyst, producing highly isotactic PP with an activity rivalling the most productive known salan-catalyst, with much higher MW capability.