Proton‐Induced Generation of Remote N‐Heterocyclic Carbene–Ru Complexes

The proton-induced RuC bond variation, which was previously found to be relevant in the water oxidation, has been investigated by using cyclometalated ruthenium complexes with three phenanthroline (phen) isomers. The designed complexes, [Ru(bpy)2(1,5-phen)]+ ([2]+), [Ru(bpy)2(1,6-phen)]+ ([3]+), and [Ru(bpy)2(1,7-phen)]+ ([4]+) were newly synthesized and their structural and electronic properties were analyzed by various spectroscopy and theoretical protocols. Protonation of [4]+ triggered profound electronic structural change to form remote N-heterocyclic carbene (rNHC), whereas protonation of [2]+ and [3]+ did not affect their structures. It was found that changes in the electronic structure of phen beyond classical resonance forms control the rNHC behavior. The present study provides new insights into the ligand design of related ruthenium catalysts.