Structure-Activity Relationships for s-Block Metal/Co(III) Heterodinuclear Catalysts in Cyclohexene Oxide Ring-Opening Copolymerizations

Abstract

In homogeneous catalysis, uncovering structure-activity relationships remains very rare but invaluable to understand and rationally improve performances. Here, generalizable structure-activity relationships apply to a series of heterodinuclear polymerization catalysts featuring Co(III) and s-block metals M(I/II) (M= Na(I), K(I), Ca(II), Sr(II), Ba(II)). These are shown to apply to polycarbonate production by the ring-opening copolymerizations (ROCOP) of cyclohexene oxide (CHO) and carbon dioxide (CO2), conducted at high (20 bar) and low (1 bar) CO2 pressures, and to polyester production by copolymerization of cyclohexene oxide and phthalic anhydride (PA). For the CHO/PA and high-pressure CHO/CO2 copolymerizations, activity increases exponentially with s-block metal acidity peaking at the Co(III)K(I) catalyst, whilst for the low-pressure CHO/CO2 copolymerization it increases linearly to the same metal combination. The polymerization kinetics fit second order rate laws and the correlations support dinuclear metallate mechanistic hypotheses. These relationships help understand and identify key metal complex structural features in synergic polymerization catalysis.