Porous Organic Polymers with Built-in N-Heterocyclic Carbenes: Selective and Efficient Heterogeneous Catalyst for the Reductive N-Formylation of Amines with CO2

A series of porous organic polymers (POPs) based on N-heterocyclic carbene (NHC) building blocks has been prepared through an octacarbonyldicobalt complex [Co-2(CO)(8)]-catalyzed trimerization of terminal alkyne groups. By changing the monomer ratio in the copolymerization, cross-linked POPs with tunable surface areas of 485-731 m(2)g(-1) and pore volumes of 0.31-0.51 cm(3)g(-1) were easily prepared. Compared with the analogues homogeneous NHC (SIPr) catalysts, the POPs exhibited an enhanced catalytic activity and high selectivity in the reductive functionalization of CO2 with amines. The extraordinary performance of the sample could be attributed to the combination of the gas enrichment (or storage) effect, enhanced in-pore concentrations of other substrates, and advantageous micropore structures of the porous polymers. Meanwhile, these catalysts can easily be separated and recycled from the reaction systems with only a slight loss of activity. This excellent catalytic performance and facile recycling of heterogeneous catalysts make them very attractive. These NHC-containing POPs may provide a new platform for catalytic transformations of CO2.