Phenalenyl-ruthenium synergism for effectual catalytic transformations of primary amines to amides.

The synthesis of amides holds great promise owing to their impeccable contributions as building blocks for highly valued functional derivatives. Herein, we disclose the design, synthesis and crystal structure of a mixed-ligand ruthenium(II) complex, [Ru(η6-Cym)(O,O-PLY)Cl], (1) where Cym = 1-isopropyl-4-methyl-benzene and O,O-PLY = deprotonated form of 9-hydroxy phenalenone (HO,O-PLY). The complex catalyzes the aerobic oxidation of various primary amines (RCH2NH2) to value-added amides (RCONH2) with excellent selectivity and efficiency under relatively mild conditions with common organic functional group tolerance. Structural, electrochemical, spectroscopic, and computational studies substantiate that the synergism between the redox-active ruthenium and π-Lewis acidic PLY moieties facilitate the catalytic oxidation of amines to amides. Additionally, the isolation and characterization of key intermediates during catalysis confirm two successive dehydrogenation steps leading to nitrile, which subsequently transform to the desired amide through hydration. The present synthetic approach is also extended to substitution-dependent tuning at PLY to tune the electronic nature of 1 and to assess substituent-mediated catalytic performance. The effect of substitution at the PLY moiety (5th position) leads to structural isomers, which were further evaluated for the catalytic transformations of amine to amides under similar reaction conditions.

Ligand-metal cooperativity in quinonoid based nickel(II) and cobalt(II) complexes for catalytic hydrosilylative reduction of nitriles to amines: electron transfer and mechanistic insight.

The sustainable production of privileged amines by the catalytic reduction of nitriles with an inexpensive silane polymethylhydrosiloxane (PMHS) holds great promise to replace conventional synthetic routes that have limited applicability and involve the use of expensive metal catalysts. The use of late 3d-metal complexes provides an excellent platform for the rational design of inexpensive catalysts with exquisite control over their electronic and structural features through metal-ligand cooperativity. In this context, we have realistically designed two complexes based on nickel(II) and cobalt(II) with a redox-active imino-o-benzoquinonato ligand. The compounds were characterized by a suite of spectroscopic methods, cyclic voltammetry and single-crystal X-ray diffraction. Both complexes showed excellent catalytic activity in transforming various organonitriles into the corresponding primary amines selectively using the inexpensive PMHS. The catalytic performance of the complexes was evaluated by various control experiments and spectroscopic studies with detailed computational calculations revealing the crucial role of the non-innocent imino-o-benzoquinonato ligand and metal(II) ion cooperativity in controlling the reactivity and selectivity of the key metal-hydride intermediates in the course of catalytic reduction.