Alcohol Dehydrogenation Catalyzed by Azo-Oxime Coordinated Ruthenium(II): A Strategic and Sustainable Route towards Site-Selective C(sp3)–H Functionalization of 9H-Fluorene

Abstract

The bidentate redox non-innocent azo-oxime ligand p-chloro-aryl-azo-oxime (p-Cl-aaOH) has been used to synthesize a robust as well as air- and moisture-stable complex trans-[Ru(p-Cl-aaO)Cl(CO)(PPh₃)₂]. It has been thoroughly characterized by various analytical, spectroscopic and Single-Crystal X-Ray Diffraction (SCXRD) analysis. Its electrochemical property has also been investigated and supported by theoretical studies. The complex has functioned as an effective ligand-based catalyst for dehydrogenation of diverse aromatic and aliphatic primary alcohols followed by selective C(sp³)–H activation of 9H-Fluorene under aerobic conditions through a tandem process. A probable catalytic cycle has been projected from relevant experiments, where the azo group of coordinated ligand plays a key role in both dehydrogenation and borrowing hydrogenation processes, while the ruthenium(II) centre behaves as a passive spectator throughout the reaction. The main advantages of this ruthenium catalyst include its simple synthetic methodology, low catalyst loading, wide substrate scope, shorter reaction times, and the ability to perform catalytic transformations at relatively lower temperatures.