Conversion of azomethine moiety to carboxamido group at cobalt(III) center in model complexes of co-containing nitrile hydratase

The Co(Ill) complex of the Schiff base ligand N-2-mercaptophenyl-2'-pyridylmethyl-enimine (PyASH), namely, [Co(PyAS)(2)]Cl (1), has been synthesized via an improved method and its structure has been determined by X-ray crystallography. The two deprotonated ligands are arranged in mer configuration around the Co(III) center and the overall coordination geometry is octahedral. The coordinated azomethine function in 1 is rapidly converted into carboxamido group upon reaction with OH-. The product is the bis carboxamido complex (Et4N)[Co(PyPepS)(2)] (2), reported by us previously. Reaction of H2O2 with 1 in DMF affords [Co(PyASO(2))(PYPePSO(2))] (3), a species with mixed imine and carboxamido-N donor centers as well as S-bound sulfinates. Further reaction with H2O2 in the presence of NaClO4 converts 3 into the previously reported bis carboxamido/sulfinato complex Na[Co(PyPepSO(2))(2)] (4). The reaction conditions for the various transformation reactions for complexes 1-4 and the structure of 3 are also reported. The mechanism of the -CH=NR + [O] --> -C(=O)NHR transformation has been discussed. The reactions reported here provide convenient alternate routes for the syntheses of Co(III) complexes with coordinated carboxamide, thiolate, and/or sulfinate donors as models for the Co-site in the Co-containing nitrile hydratase(s).