Highly active primary amine ligated Ru(II)-arene complexes as selective catalysts for solvent-free N-alkylation of Anilines

Abstract

Efficient Ru(II) catalysts with substituted aniline based ligands were synthesized having chemical formula [Ru(η6-p-cymene)Cl2(L1)] [Ru-1] and [Ru(η6-p-cymene)Cl2(L2)] [Ru-2] (where, L1 = 3,5-bis(trifluoromethyl)aniline and L2 = 3,4,5- trimethoxy aniline). The structural features of both the complexes were authenticated by ESI-MS, 1H and 13C NMR, FT-IR, elemental analyses, and single-crystal X-ray diffraction studies. Catalytic performance of both [Ru-1] and [Ru-2] was investigated for conversion of primary amine to secondary amine using alcohols under milder and solvent-free conditions and compared with the reported aniline-based Ru(II)-arene complex [Ru-3]. Among them, [Ru-1] could achieve 100% selectivity towards mono N-alkylated amines with &gt

99% conversion without formation of any imine derivatives. The results suggested that the lone pair of electrons of benzyl alcohol binds easily to the electron-deficient Ru(II) center of [Ru-1] catalyst making it more effective compared to electron-rich [Ru-2] and [Ru-3] catalysts. The catalytic performance of [Ru-1] demonstrates that it is one of the most active primary amine ligated Ru(II) based catalytic systems for N-alkylation of anilines under milder and solvent-free conditions. © 2023 Elsevier B.V.