Binuclear Ruthenium (II) Catalyzed Selective α-Alkenylation of Amide via Acceptorless Dehydrogenative Coupling of Alcohols

Abstract

Herein, we report an effective catalytic methodology for the construction of α,β-unsaturated amides via acceptorless dehydrogenative coupling (ADC) of alcohols using newly synthesized binuclear ruthenium (II) complex [(η⁶-p-cymene)₂Ru₂Cl₂(μ-L)] (where L = N′-4-fluoro benzoyl-4-fluorobenzohydrazide) as catalyst. The structural characterization of the newly synthesized ruthenium complex has been established using analytical and various spectroscopic techniques (FT-IR, UV–vis, and NMR). Further, the molecular structure of the complex has been authenticated by a single-crystal X-ray diffraction method. The catalytic system displaces a wide range of α,β-unsaturated amides (16 examples), which have been obtained from the reaction of diverse primary alcohols and aryl amide with maximum of 93% of yield. The protocol for α-alkenylation of amide involves through C-C bond formation utilizing 0.5 mol% of catalyst loading with the release of release water and hydrogen gas as the only by-products. The control experiments evidence the initial dehydrogenation of alcohols into their corresponding aldehydes and C=C bond formation through aldol condensation. In addition, a large-scale synthesis of one of the amides (E)-3-(4-methoxyphenyl)-N-phenyl acrylamide has been performed with the yield of 78%, which proves the effectiveness of the present catalytic protocol.