Transition metal complexes with N-heterocyclic carbene ligands: From organometallic hydrogenation reactions toward water splitting

Abstract N -Heterocyclic carbenes (NHCs) as a new class of ligands for the stabilization of catalytic metal complexes for catalytic water splitting are discussed. An overview over current applications of NHC stabilized metal catalysts in organometallic catalysis involving hydrogen in transfer hydrogenation, hydrogenation and acceptorless dehydrogenation is presented. A focus is placed on the role of the NHC ligand structure and utilized metal centers. The current status of NHC stabilized catalytic centers within the inter- and intramolecular photocatalytic hydrogen formation and water oxidation is reviewed. The very interesting photochemical properties of a new class of ruthenium complexes with NHC-carbene containing potential bridging ligands are discussed. These complexes can bind catalytic metal centers at the NHC sphere. The so formed photochemical devices are active photocatalysts for hydrogen evolution.