CO₂固定化のための二官能性分子触媒：相乗効果を高める構造最適化

抄録

We developed various metalloporphyrins as bifunctional catalysts for the synthesis of cyclic carbonates from epoxides and CO₂ under solvent-free conditions. The structures of the bifunctional catalysts were optimized step by step. As a result, a Zn porphyrin bearing eight nucleophiles at the meta positions showed a high turnover number (TON=240,000) at 120 °C at 1.7 MPa CO₂ and catalyzed the reaction even at atmospheric CO₂ pressure (balloon) at ambient temperature (20 °C). Triporphyrin catalysts showed very high catalytic activity: TON=220,000 and TOF=46,000 h^-1 for the Mg triporphyrin, and TON=310,000 and TOF=40,000 h^-1 for the Zn triporphyrin. The high catalytic activity of these bifunctional catalysts was due to the cooperative action of Mg²⁺ or Zn²⁺ and Br^- and a conformational change (induced-fit) of the quaternary ammonium cation.