Copolymerization of CHO/CO2 catalyzed by a series of aluminum amino-phenolate complexes and insights into structure-activity relationships

Study of Preparation and Properties of Stereoregular Poly(cyclohexenylene carbonate)

Fixing carbon dioxide as a polymer material is an effective and environmentally beneficial approach for reducing the harm of CO₂ greenhouse gas. In this paper, carbon dioxide and cyclohexene oxide were used as co-monomers, and a chiral binuclear cobalt complex with a biphenyl linker was employed as the catalyst to successfully prepare a poly(cyclohexenylene carbonate) with high stereoregularity. The influence of catalyst structure, CO₂ pressure, and operating temperature on the copolymerization rate and polymer structure were systematically investigated. Optimal catalyst structure and operating conditions were determined, resulting in an excellent poly(cyclohexenylene carbonate) with a stereoregularity as high as 93.5%. Performance testing revealed that the polyester had a molecular weight of approximately 20 kg/mol, a glass transition temperature of 129.7 °C, an onset decomposition temperature of 290 °C, and a tensile strength of 42.8 MPa. These results demonstrate high thermal stability and mechanical strength, indicating the potential for expanding the applications of aliphatic polycarbonate materials.

Group 13 salphen compounds (In, Ga and Al): a comparison of their structural features and activities as catalysts for cyclic carbonate synthesis

Many complexes based on group 13 elements have been successfully applied as catalysts for the synthesis of cyclic carbonates from epoxides and CO₂ and to date these have provided some of the most active catalysts developed. It is notable that most reports have focused on the use of aluminium-based compounds likely because of the well-established Lewis acidity of this element and its cost. In comparison, relatively little attention has been paid to the development of catalysts based on the heavier group 13 elements, despite their known Lewis acidic properties. This study describes the synthesis of aluminium, gallium and indium compounds supported by a readily prepared salphen ligand and explores both their comparative structures and also their potential as catalysts for the synthesis of cyclic carbonates. In addition, the halide ligand which forms a key part of the compound has been systematically varied and the effect of this change on the structure and catalytic activity is also discussed. It is demonstrated that the indium compounds are actually, and unexpectedly, the most active for cyclic carbonate synthesis, despite their lower Lewis acidity when compared to their aluminium congeners. The experimental observations from this work are fully supported by a Density Functional Theory (DFT) study, which provides important insights into the reasons as to why the indium catalyst with bromide, [InBr(salphen)], is most active.

Dinuclear Nickel Complexes Using Hexadentate Benzothiazole-Based Diamine-Bisphenolate Ligands: Highly Active Catalysts for Copolymerization of Carbon Dioxide with Epoxides

We reported for the first time the utilization of hexadentate benzothiazole-based diamine-bisphenolate ligands to synthesize structurally well-characterized dinickel dicarboxylate complexes and studied their catalysis for copolymerization of carbon dioxide with epoxides. Dinickel carboxylate complexes having a 1,3-diamine-bridged backbone were demonstrated to be high-performance catalysts for alternating copolymerization of CO₂ and cyclohexene oxide (CHO) with high product selectivity. Particularly, acetate-supported nickel complex 2 enabled us to promote such CO₂-copolymerization of this kind with a maximum turnover frequency of up to 2600 h^-1 and gave good molecular weight controllability under high-pressure conditions. It is worth noting that bimetallic Ni catalyst 2 was also capable of mediating the catalytic CO₂-polymerization of alicyclic epoxides at atmospheric pressure. Kinetic investigations of CO₂/CHO copolymerization by 2 allowed us to determine the rate equation of -d[CHO]/dt = k_p[2]¹[CHO]¹, and such catalysis exhibited a first-order dependence on both dinickel complex and CHO concentrations.

Indium-Catalyzed CO2/Epoxide Copolymerization: Enhancing Reactivity with a Hemilabile Phosphine Donor

Group 13 metal complexes have emerged as powerful catalysts for transforming CO₂ into added-value products. However, direct comparisons of reactivity between Al, Ga, and In catalysts are rare. We report aluminum (1), gallium (2), and indium (3) complexes supported by a half-salen H[PNNO] ligand with a pendent phosphine donor and investigate their activity as catalysts for the copolymerization of CO₂ and cyclohexene oxide. In solution, the P-donor is dissociated for the Al and Ga complexes while for the In complex it exhibits hemilabile behavior. The indium complex shows higher conversion and selectivity than the Al or Ga analogues. The mechanism of the reaction was studied by NMR and FTIR spectroscopy experiments as well as structural characterization of off-cycle catalytic intermediate indium trichloride complex [(PNNO)InCl₃][TBA] (4). This study highlights the impact of a hemilabile phosphine group on group 13 metals and provides a detailed analysis of the initiation step in CO₂/epoxide copolymerization reactions.