Bifunctional catalysts based on 2-amino-1,10-phenanthroline-containing podands for cyclic carbonates synthesis from CO2 and epoxides under mild conditions

Abstract

A new series of polytopic ligands based on 1,10-phenanthroline and polyoxadiamines has been synthesized through S_NAr amination between 2-chloro-1,10-phenanthroline and diamines of various structures. The obtained podands were investigated as polytopic ligands for potassium and zinc ions in the industrially important reaction of cyclic carbonates synthesis from CO₂ and epoxides under mild conditions (p(CO₂) = 1 atm., T = 60–80 °C). The advantage of 1,11-diamino-3,6,9-trioxaundecane functionalized by 1,10-phenanthroline units compared to the diamine itself is demonstrated. It is revealed that heteroarylated 1,11-diamino-3,6,9-trioxaundecane can be used as a catalyst in the presence of KI (2 mol.%) with a low loading of the ligand (0.2 mol.%) instead of the usually employed 5–10 mol.% for unfunctionalized podands. Under these reaction conditions mono-substituted cyclic carbonates of various structures have been synthesized in excellent preparative yields ranging from 87 to 99%. Coordination of two Zn(II) ions to both 1,10-phenanthroline moieties has been shown to provide additional enhancement of catalytic activity. The catalysts demonstrate excellent stability and can be reused at least in 6 cycles.