CH(phenol)-Bridged Bis(imino)pyridines as Compartmental Supports for Diiron Precatalysts for Ethylene Polymerization: Exploring Cooperative Effects on Performance

A family of six CH(phenol)-bridged bimetallic bis(imino)pyridine-iron(II) chlorides, CH(C6H4-4-OH){2′-(4-C6H2-2,6-(R1)2N═CMe)-6′-(2″,6″-(R2)2-4-(R3)C6H2N═CMe)C5H3N}2Fe2Cl4 [R1 = R2 = Me, R3 = H, Fe1; R1 = R2 = Et, R3 = H, Fe2; R1 = Me, R2 = Et, R3 = H, Fe3; R1 = Me, R2 = i-Pr, R3 = H, Fe4; R1 = R2 = R3 = Me, Fe5; R1 = R2 = Et, R3 = Me, Fe6], has been synthesized by the reaction of the corresponding compartmental ligand with 2 equiv of FeCl2·4H2O. The molecular structure of Fe6 reveals an intramolecular Fe···Fe separation of 10.152 Å, with pairs of Fe6 assembling through intermolecular OH···Cl hydrogen bonding interactions. On activation with MAO or MMAO, Fe1–Fe6 exhibited both good thermal stability and very high activity for ethylene polymerization with the least sterically bulky compound, Fe1, being the standout performer (up to 2.43 × 107 g·mol–1(Fe)·h–1 at 60 °C). Notably, Fe1/MAO showed almost double the activity of a structurally related mononuclear catalyst while the resultant polyethylene exhibited much higher molecular weight. In general, the polymeric materials are highly linear and have a tendency to display bimodal distributions that is influenced by the amount of cocatalyst employed. End-group analysis of the polymers generated using MMAO activation reveals chain ends composed of vinyl and saturated groups (propyl and isobutyl), while with MAO, a preference for propyl end groups is observed.