Metal induced cleavage of amide bonds. Part 3. Cleavage of aromatic amides and isolation of [ cis-α-Co(trien) (salicylamide)](ClO 4) 2 ( I), Co(tren)(pyrazine-2-carboxylato)](ClO 4) 2·2H 2O ( II) and [Co(tren)(pyrazine-2,3-dicarboxylatomonoamide)](ClO 4)Cl ( III)

Abstract

Three aromatic amides were allowed to interact with cis-[dichloro(N 4)Co] + cations in water solutions at controlled pH ranging from 7.0 to 7.5. N 4 is a linear or a branched tetra-amine, such as trien or tren (trien = 1,4,7,10-tetraazadecane; tren = tris-(2-aminoethyl)amine). In one case(II), the effective result is displacement of the cis-dichloride ligands, amide hydrolysis and trapping of the generated carboxylate as a bidentate ligand to the cobalt amine fragment. In two others ( I and III), the amide was trapped intact as a bidentate ligand to cobalt in which the NH 2 fragment was dangling, unbound. These results are in line with previous studies carried out here on metal-induced amide and peptide hydrolyses. The products were isolated and characterized by NMR and X-ray diffraction. In all of our previous work the amides were aliphatic. We wanted to determine whether similar metal-induced hydrolytic cleavage would occur with aromatic amides. The answer is that the results depend on the conditions in which the reactions are carried out – details are given below. It is notable that in all three cases, some of the perchlorate oxygens are directly atop the π clouds of the aromatic rings, as discussed in the text. For example, in compound ( III) three of the oxygens are over the π cloud at average distances of less than 3.5 Å.