Reversible Photoisomerization in a Ru cis-Dihydride Catalyst Accessed through Atypical Metal–Ligand Cooperative H₂ Activation: Photoenhanced Acceptorless Alcohol Dehydrogenation

Abstract

Dehydrohalogenation of pyridine-derived pincer ruthenium complexes often leads to dearomatized moieties, such as in Milstein’s PNN-Ru­(CO)­(Cl)­(H) (1Py) catalyst. Thus, we were surprised to find an aromatized κ3-N,C,P binding mode in the lutidine-derived bidentate analogue [{LutP′}­Ru­(CO)­(H)­(PPh3)] (2), instead of a dearomatized compound, upon dehydrohalogenation of [{LutP}­Ru­(CO)­(Cl)­(H)­(PPh3)] (1). The reaction of 2 with H2 results in the formation of the cis-dihydride [{LutP}­Ru­(CO)­(H)2(PPh3)] (3), and labeling studies confirm cooperative metal–ligand activation. 3 exhibits reversible photoisomerization, forming another cis-dihydride isomer (4) upon irradiation. The lability of 4 toward ligand substitution was leveraged to demonstrate photoenhanced H2 production via acceptorless alcohol dehydrogenation. Labeling studies implicate metal–ligand cooperative (MLC) processes during the photocatalytic reaction, but they appear to be off-path processes on the basis of our mechanistic study of the system. The latter emphasizes that aromatization/dearomatization may not be necessary for acceptorless transformations, which is generally consistent with several contemporary studies on analogous Ru catalysts.

Photoredox (NN)Mn(I) Catalysed Acceptorless Dehydrogenation: Synthesis of Amides, Aldehydes and Ketones

“…Based on the control experiments and existing literature reports, [7b,8,13] a plausible reaction mechanism was proposed for amide formation (Scheme 3). Under UV‐A light irradiation and in the presence of NaH, Cat.…”