Cation-π interactions enabling hard/soft Ti/Ag heterobimetallic cooperativity in lactide ring-opening polymerisation

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

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.

Salt additives as activity boosters: a simple strategy to access heterometallic cooperativity in lactide polymerisation

Inorganic salt additives can activate carbonyl groups towards organic addition reactions. Here, we translate this concept to ring-opening polymerisation for the first time, generating heterometallic ProPhenol catalysts in situ, which show similar activity enhancements to pre-formed heterometallic complexes. Extremely high activities are observed, with K/Mg and K/Ca combinations converting >85 eq. lactide in 5 s at room temperature.