Synthesis of N-alkylated amines via alcohol dehydrogenation catalyzed by a bis-azo-diamido coordinated ruthenium(iii) complex

Abstract

An interesting ruthenium(III) complex, trans-[Ru(H₂L)Cl(PPh₃)], has been synthesized using a redox-active tetradentate bis-azo diamine ligand (H₄L). This complex represents the first example of a structurally robust, air- and moisture-stable coordination compound featuring a redox non-innocent ligand that provides a unique N4 donor set comprising both strong π-acidic (azo) and σ-donating (amido) groups. The complex has been comprehensively characterized by elemental analysis, various spectroscopic techniques, and single-crystal X-ray diffraction (SCXRD) studies. Its electrochemical behaviour has been investigated through cyclic voltammetry and analyzed using density functional theory (DFT) calculations. In catalysis, it efficiently mediates the dehydrogenation of primary alcohols and their subsequent coupling with aromatic amines to afford N-alkylated amines via the “Borrowing Hydrogenation” (BH) pathway. Mechanistic investigations indicate that the redox-active azo units drive the catalytic cycle, while the Ru(III) center remains largely redox-inactive. Key advantages of this catalytic protocol include a straightforward synthetic route, low catalyst loading, broad substrate tolerance, short reaction times, and operation under relatively mild conditions.