Water-Soluble IrIII N-Heterocyclic Carbene Based Catalysts for the Reduction of CO2 to Formate by Transfer Hydrogenation and the Deuteration of Aryl Amines in Water

Two new water-soluble [IrI2(AcO)(bis-NHC)] complexes (NHC= N-heterocyclic carbene) incorporating a sulfonate functionality have been synthesized. The two complexes have been tested in the reduction of CO2 with H-2 and iPrOH, and their activity has been compared with similar species without the sulfonate moiety. In both reactions, the complex with the two ab-normally bound NHCs shows the best catalytic efficiencies, due to the higher sigma-electron-donor character of the ligand. Remarkably, the activities obtained for the reduction of CO2 under the transfer hydrogenation conditions are the best reported to date in terms of TON value (max. TON = 2700). The two new complexes have also shown very good activity in the selective deuteration of arylamines, a process that is known to proceed through a chelate assisted N-directed process.