Homoleptic ruthenium complexes with N-heterocyclic carbene ligands as photosensitizers in the photocatalytic generation of H2 from water

• Published in: Journal of organometallic chemistry 2019-10, Vol.898, p.120880, Article 120880
• Main Authors: Torres, Javier, Carrión, M. Carmen, Leal, Jorge, Castañeda, Gregorio, Manzano, Blanca R., Jalón, Félix A.
• Format: Article
• Language: English
• Subjects: Hydrogen generation; N-heterocyclic carbenes; Photocatalysis; Photosensitizer; Ruthenium
• ISSN: 0022-328X; 1872-8561
• DOI: 10.1016/j.jorganchem.2019.120880

There is great interest in the catalytic photoreduction of water to give hydrogen as a fuel to harness solar energy and a series of ruthenium complexes has been synthesized and tested as photosensitizers in this photoreduction process. There are very few precedents for N-heterocyclic carbene complexes in this field. The complexes obtained in this work were of the type [Ru(:CˆNˆC:)2](PF6)2 and [Ru(NˆC:)3](PF6)2 with N-heterocyclic carbene ligands derived from pyridine and imidazole heterocycles with methyl or benzyl substituents. The photophysical properties of the complexes were studied. Some complexes were luminescent and, although the quantum yields were rather low, the lifetimes were quite high (1.5–1.7 μs). The emissive complexes behave as photosensitizers in the generation of H2 using [Co(bpy)3]Cl2 (bpy = 2,2′-bipyridine) as catalyst and triethanolamine (TEOA) as the sacrificial reductant through an oxidative quenching mechanism. The amount of hydrogen obtained was higher for the benzyl derivative. Homoleptic ruthenium complexes of the type [Ru(:CˆNˆC)2](PF6)2 and [Ru(NˆC)3](PF6)2 with N-heterocyclic ligands were synthesized and tested as photosensitizers in the photocatalytic H2 production from water with a cobalt catalyst. The luminiscent complexes with lifetimes of 1.5–1.7 μs were active in the process through a mechanism of oxidative quenching. [Display omitted] •Catalytic photoreduction of water to give hydrogen as a fuel to harness solar energy.•Luminiscent Ru complexes NHC ligands as photosensitizers in H2 production.•Tridentate ligands behave better than bidentate ligands.•Modifications of the ligand provides helpful insights to get better photosensitizers.