Metal-salen-bridged ionic networks as efficient bifunctional solid catalysts for chemical fixation of CO2 into cyclic carbonates

A series of bifunctional heterogeneous ionic polymer networks M-Salen-TBB-R were developed by reacting archetype of metal-salophen wtih 1,2,4,5-tetrakis(bromomethyl)benzene, followed by treatment with ionic liquid groups. Various techniques such as H-1 NMR, TGA, CHN elemental analysis, SEM, FTIR, XPS, and ICP-AES were used to characterize these catalysts. A number of attractive features like highly cross-linked polymer framework, abundant active sites of Lewis acid metal centers and nucleophile Br-, and various N-containing functional cations that endow the resultant catalysts with an expected talent for fixation of carbon dioxide (CO2) under mild and solvent-cocatalyst-free conditions. The catalytic tests by comparison to various synthesized counterparts well demonstrate that this catalyst exhibit excellent activity and selectivity for the cycloaddition of CO2 with epoxides, and the catalyst can be conveniently recovered and reused. The durable cross-linked network structure of catalyst and the cooperative effect between the metal center, Br-, and organic cations are responsible for the catalyst's good performances in cycloaddition reactions. (C) 2017 Elsevier B.V. All rights reserved.