Amide bond cleavage initiated by coordination with transition metal ions and tuned by an auxiliary ligand

The reaction of ligand L, N,N-bis(pyridin-2-ylmethyl)acetamide, with five transition metal salts, FeCl3·6H2O, CuCl2·2H2O, Cu(ClO4)2·6H2O, ZnCl2 and K2PtCl4/KI, produced five metal complexes, [(μ-O)(FeClL′)(FeCl3)] (1), [CuLCl2] (2), [CuBPA(ClO4)(CHCN)] ClO4 (3), [ZnLCl2] (4) and [PtLI2] (5), where L′ = 1-(2,4,5-tri(pyridin-2-yl)-3-(pyridin-2-ylmethyl)imidazolidin-1-yl)ethanone which formed in situ, and BPA = bis(pyridin-2-ylmethyl)amine. The ligand and complexes were characterized by a variety of spectroscopic techniques including X-ray single crystal diffraction where applicable. Depending on the metal ion and auxiliary ligand of the complex, the acetyl group of the ligand L could be either intact or cleaved. When ferric chloride hexahydrate was used, the deacetylation proceeded even further and a novel heterocyclic compound (L′) was formed in situ. A possible mechanism was proposed for the formation of the heterocyclic compound found in complex 1. Our results indicate that to cleave effectively an amide bond, it is essential for a metal centre to bind to the amide bond and the metal centre is of sufficient Lewis acidity.