Metal induced cleavage of amide bonds. Part 3. Cleavage of aromatic amides and isolation of [cis-alpha-Co(trien) (salicylamide)](ClO4)(2) (I), Co(tren)(pyrazine-2-carboxylato)](ClO4)(2)center dot 2H(2)O (II) and [Co(tren)(pyrazine-2,3-dicarboxylatomonoamide)](ClO4)Cl (III)

摘要

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 -NH2 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 pi clouds of the aromatic rings, as discussed in the text. For example, in compound (III) three of the oxygens are over the pi cloud at average distances of less than 3.5 angstrom. Published by Elsevier B. V.