Frederica Butler

Earth-abundant metal catalysts are important for future polymer production. Iron is both an earth-abundant and non-critical element and is attractive for catalysis. Here, a series of heterodinuclear catalysts incorporating Fe(III) with different s-block metals, M(I/II) = K(I), Na(I), Sr(II), Ba(II), an Fe(II)K(I) catalyst, and a monometallic Fe(III) catalyst are reported for the ring-opening copolymerization of cyclohexene oxide and phthalic anhydride to produce polyesters. The lead Fe(III)K(I) catalyst achieves a high turnover frequency of 3478 ± 51 h–1 (1:400:7000, [catalyst]0:[PA]0:[CHO]0, 140 °C) while retaining quantitative (>99%) polyester selectivity. Its performance is competitive with the best catalysts in the field. Using microscale calorimetry, the polymerization rate law, rate coefficients and transition state energies are determined. These data are rationalized by a dinuclear catalytic mechanism and allow for insight into the influence of varying catalyst structural features on the reaction enthalpy and entropy barriers. The results inform upon the physical origins of high catalytic activity and provide mechanistic insights useful for future catalyst design.

Carbon dioxide waste, plastic waste and waste electronic and electrical equipment (WEEE) are three prevalent forms of waste in modern society. The chemical sciences have a crucial role to play in transforming these waste streams into valuable products.

Intermetallic synergy can be useful to both enhance catalytic performance and access diverse chemistries, but understanding and predicting the most effective metal combinations remains a challenge. This perspective focuses on a common class of homogeneous heteronuclear catalysts which combine transition metals (M(II/III)) with Group III, f-, or s-block metals (M’(I–III)) in phenoxy-imine-ether donor ligands. Independent investigations into these heteronuclear complexes across different fields of catalysis, including electrocatalysis, polymerization catalysis, and small-molecule asymmetric catalysis, have all demonstrated the benefits of intermetallic cooperativity. In both electrocatalysis and polymerization catalysis, similar quantified structure-performance relationships, relating catalytic performance to metal Lewis acidity, have been discovered. This selective perspective article focuses on highlighting the most recent insights and quantified structure–activity relationships in electro- and polymerization catalysis. We then apply the insights and methods, developed separately in these two fields of catalysis, to reanalyze previously reported data for catalytic asymmetric organic transformations. The same quantified structure-performance (i.e., activity or selectivity) trends appear to apply in this third field of homogeneous catalysis. These generally applicable, quantified structure–activity relationships apply to related synergistic heterometallic catalysts across all three disparate fields of chemistry ─ this finding is both unexpected and very helpful in providing a clearer understanding of how to design catalysts for successful intermetallic synergy. This perspective highlights both the fundamental understanding of such catalytic synergy and the analytical methods used to investigate it. The objective is to provide a guide for both current and future researchers to measure synergistic interactions and to apply those principles to rational catalyst design.

The ring-opening copolymerization of propene oxide and carbon dioxide is an effective route to make polycarbonates. Catalysts showing high activities, high polymer selectivities, molecular weight control, and tolerance to impurities are rare. Here, a series of four Co(III)Na(I) catalysts are tested for the ring-opening copolymerization of propene oxide and carbon dioxide. The complexes have systematic variations in the ligand structure in which both Co(III) and Na(I) binding sites are modified. Significant differences in catalyst performance are observed, with the lead catalyst featuring six oxygen donors and an ethylene diamine linker. This catalyst shows excellent activity and high poly(propene carbonate) selectivity at elevated temperatures (TOF = 1428 h^–1, poly(propene carbonate) selectivity = 98%, 20 bar CO₂, 70 °C), outperforming analogous Co(III)K(I) catalysts. These results inform on the optimal coordination environment and operating conditions for the Co(III)Na(I) catalysts and highlight the benefits of using Na(I) relative to heavier s-block metals in the heterodinuclear catalysts.

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.

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.