Hollow Microporous Organic Polymer@Hypercrosslinked Polymer Catalysts Bearing N-Heterocyclic Carbene–Iron Species for the Synthesis of Biomass-Derived Polymer Platforms

A hollow catalyst bearing N-heterocyclic carbene (NHC)–Fe species was synthesized using a hollow microporous organic polymer (HMOP) as a template. In the presence of HMOP, the Friedel–Crafts reaction of 1,3,5-tri(bromomethyl)benzene induced the loading of hypercrosslinked polymer (HCP) onto HMOP. The resultant HMOP@HCP material bearing benzyl bromide groups could be further modified with N-methylimidazole to form HMOP@HCP bearing imidazolium salt (HMOP@HCP-Im). The use of KOtBu, followed by Fe coordination, generated HMOP@HCP bearing NHC–Fe species (HMOP@HCP-Fe). HMOP@HCP-Fe showed superior catalytic performance to nonhollow HCP-Fe in the transesterification of dimethyl furan 2,5-dicarboxylate to furan diols, polymer platforms of polyurethane. In addition, HMOP@HCP-Fe showed near-quantitative yields for five successive catalytic runs.