Tolerant Bimetallic Macrocyclic [OSSO]-Type Zinc Complexes for Efficient CO₂ Fixation into Cyclic Carbonates

Abstract

A new type of sustainable bimetallic zinc complexes bearing macrocyclic thioetherphenolate [OSSO]-type ligands has been developed and employed toward the chemical fixation of carbon dioxide into cyclic carbonates. The effects of reaction variables such as temperature, time, pressure, and molar ratio of epoxide to catalyst on the catalytic performance were systematically investigated. Based on the observations from structural and spectroscopic analyses, a plausible catalytic mechanism for the present reaction system was proposed, in which a Lewis acidic zinc center activates the epoxide and a nucleophilic halide counterion from the cocatalyst to ring open the activated epoxide. The two zinc centers are situated sufficiently close to each other to rationally allow a synergistic effect in the cycloaddition. The macrocyclic thioetherphenolate [OSSO]-type catalyst showed excellent conversions and selectivity for CO2 fixation into cyclic carbonates from a broad range of terminal epoxides, including bis-epoxides and biomass-derived epoxides substrates. Additionally, these catalysts demonstrate high stability to moisture and oxygen, resistance to many kinds of impurity, and good recyclability with negligible losses in catalytic activity.

Ring-opening polymerization of ε-caprolactone mediated by a di-zinc complex bearing a macrocyclic thioether-phenolate [OSSO]-type ligand

“…19 Furthermore, metal complexes with bimetallic architectures facilitate the cooperation between two metal centers under certain circumstances, which has been proven to be one of the attractive strategies in improving their activities in mediating organic transformations 22 and polymerizations. 9,23,24 More recently, we revealed that air-stable dinuclear zinc complexes supported by the macrocyclic thioetherphenolate [OSSO] ligand (Di-[OSSO] ZnX) demonstrated high efficiency toward the coupling reaction of epoxides and carbon dioxide, 25 where the activated epoxide reacts with the nucleophilic cocatalyst to generate real active species of metal-alcoholate (Zn-OR) intermediates under the [OSSO]-type di-zinc complex/TBAB binary catalytic system.…”

Recent Advancements in Metal‐catalysts Design for CO2/Epoxide Reactions

“…A cyclic ligand, designed combining the successful example of the Robson-type ligand employed in the CO 2 /epoxide reactions with various metal centers by Williams and coworkers, [59][60][61][62] with the beneficial role played by the soft sulfur atom in the ligand design for the CO 2 /epoxides coupling, [63] was reported by He and coworkers (Figure 14). [64] In particular they reported that the bimetallic complexes 50-53 activated by TBAB displayed higher activity (TOF up to 4188 h À 1 for the complex 52) in the conversion of PO to PC compared to the corresponding mononuclear complex 53 (TOF = 1392 h À 1 ) under the same reaction conditions (3 MPa; 130 °C, 1 h).…”

Cycloaddition of di-substituted epoxides and CO2under ambient conditions catalysed by rare-earth poly(phenolate) complexes

“…A large number of catalysts have been developed to catalyse the cycloaddition reaction, including transition metals (e.g., Cr, [15][16][17] Fe, [18][19][20][21] Co, [22][23][24][25][26][27] and Zn [28][29][30][31][32][33] ), main group metals (e.g., Mg, [34][35][36] Al, [37][38][39][40][41][42] Ca [43][44][45][46] ), rare-earth metal catalysts [47][48][49][50][51][52][53][54][55][56][57] and organocatalysts. 5,[58][59][60][61][62][63]…”

“…A large number of catalysts have been developed to catalyse the cycloaddition reaction, including transition metals ( e.g. , Cr, 15–17 Fe, 18–21 Co, 22–27 and Zn 28–33 ), main group metals ( e.g. , Mg, 34–36 Al, 37–42 Ca 43–46 ), rare-earth metal catalysts 47–57 and organocatalysts.…”