Ruthenium(II)-Catalyzed Hydrogenation and Tandem (De)Hydrogenation <i>via</i> Metal–Ligand Cooperation: Base- and Solvent-Assisted Switchable Selectivity
Rahul Daga Patil, Sanjay Pratihar
Abstract
A versatile, selective, solvent (methanol vs ethanol)- and base (potassium vs lithium carbonate)-assisted switchable synthesis of saturated ketone and α-methyl saturated ketone from α,β-unsaturated ketone is developed. Mechanistic aspects, evaluated from spectroscopic studies, in situ monitoring of the reaction progress, control studies, and labeling studies, further indicate the involvement of a tandem dehydrogenation–condensation–hydrogenation sequence in the reaction, in which the interconvertible coordination mode (imino N → Ru and amido N–Ru) of coordinated imidazole with Ru(II)–para-cymene is crucial, without which the efficiency and selectivity of the catalyst are completely lost. The catalyst demonstrates good efficiency, selectivity, and functional group tolerance and displays a broad scope (69 examples) for monomethylation and hydrogenation of unsaturated chalcones, double methylation of ketones, and N-methylation of amines.