Unsaturated NHC Complexes Immobilized by the Backbone: Synthesis and application

The synthesis and an exemplary catalytic application of a SBA-15-supported rhodium-N-heterocyclic carbene (NHC) complex is reported. In contrast to the conventional method of immobilization of unsaturated NHC complexes, the rhodium-NHC compound described here is connected to the SBA-15 surface by a linker originating from the backbone of the unsaturated NHC ligand. The unique characteristics of the new immobilization mode enable the supported NHC complexes to maintain two unchanged "wing-tip" ligands. This method of immobilization of unsaturated NHC complexes provides a new way to maintain the original configuration of homogeneous NHC complexes in the heterogenized catalytic system. The immobilized rhodium-NHC catalyst is used in a hydrogenation reaction with styrene as substrate.