Regioselective cyclometallation of N-methyl-N-(naphthalen-2-ylmethyl)-2-(pyridin-2-yl)ethanamine with palladium(II) acetate and catalytic reduction of various functional groups

Abstract

The preparation of novel unsymmetrical, tridentate ligand, N-methyl-N-(naphthalen-2-ylmethyl)-2-(pyridin-2-yl) ethanamine (1), has been described. Ligand 1 reacts with Pd(OAc)2 to give the corresponding cyclometallated complex, which could not be isolated. The substitution reactions of the in-situ prepared cyclometallated complex with LiCl/LiBr afforded the corresponding palladacycles (3-((methyl(2-(pyridin-2-yl)ethyl)amino)methyl)naphthalen-2-yl)palladium(II) chloride (2) /bromide (3). Both the complexes having one γ′-C–H, N(alkyl) and N(aryl) atom, form square planar complexes with halogens (Cl for 2 and Br for 3) as the fourth ligand. Interestingly, ligand 1 has two ortho-activated (γ-C–H and γ′-C–H) hydrogen atoms of the naphthyl ring, however, only γ′-C–H atom is palladated. The prepared CNN pincer –Pd complex 3 has been investigated for its catalytic property in the reduction of various functional groups under mild reaction conditions. In addition, ligand 2-(2-bromophenyl)-1H-benzo[d]imidazole (4) and its palladium (II) complex bis-[2-(2-bromophenyl)-1H-benzo[d]imidazole)PdCl2 (5) have also been prepared.