摘要
Herein,we report the application of four amino-tris(phenolate)-based metal complexes incorporating Ti(IV)or Zr(IV)centres(2a-3b)as homogeneous catalysts for the conversion of CO_(2)and epoxides into cyclic carbonates.The four complexes were synthesised,characterised and then evaluated in combination with tetrabutylammo-nium iodide,bromide or chloride as binary catalytic systems for the reaction of CO_(2)with 1,2-epoxyhexane as epoxide substrate at 12 bar CO_(2)pressure and 90?C for 2 h.The catalytic systems comprising the two Ti(IV)complexes(2a and 2b)showed similar performance.One notable exception was the catalytic system consisting of titanium complex 2b,bearing an axial Cl-ligand,and tetrabutylammonium chloride,which displayed higher catalytic activity compared to other titanium-based systems.Even higher activity was achieved with Zr(IV)complex 3a,bearing an axial isopropoxide ligand,which reached turnover numbers(TON metal)up to 1920 for the reaction of CO_(2)with 1,2-epoxyhexane at 12 bar CO_(2)pressure and 90?C for 2 h.This performance is comparable with that of state-of-the-art catalysts for this reaction.The catalytic system consisting of complex 3a and tetra-butylammonium bromide was explored further by investigating its applicability with a broad substrate scope,achieving quantitative conversion of several epoxides with CO_(2)into cyclic carbonate products at 90?C and 12 bar CO_(2)pressure for 18 h.The selectivity towards the cyclic carbonate products was?98%for all studied terminal epoxides and?80%for all examined cyclohexene-type epoxides.
