Epoxide activation by a silver phosphonate for heterogeneous catalysis of CO2 cycloaddition

Abstract

Hydrothermal reaction of silver nitrate and a tetraphosphonic acid (H₈L) affords a novel coordination polymer, with the general formula, [Ag₁₀(H₃L)₂(H₂O)₂(4,4′-bipy)], denoted as compound 1. It is built from extended ⋯Ag–O–P–O⋯ chains and organic linkers to form a 3D network. In its structure, three of four phosphonyl groups of the organic ligand are protonated, endowing compound 1 with rich Brønsted acid sites. With Brønsted and Lewis acidic sites, the catalytic activity of 1 was investigated through cycloaddition reaction of CO₂ and epoxides, and the results displayed an excellent performance. Besides, the heterogeneous nature of compound 1 was proved by five cycle experiments with no significant compromise on the activity, indicating the silver phosphonate as an excellent catalyst for CO₂ chemical fixation.