Toward model complexes of Co-containing nitrile hydratases:: synthesis, complete characterization and reactivity toward ligands such as CN- and NO of the first square planar CoIII complex with two different carboxamido nitrogens and two thiolato sulfur donors

A [Co-III(N2S2)]NEt4 complex, with two carboxamido nitrogens and two alkylthiolato sulfurs, was prepared from N,N'-(2-thioacetyl-isobutyryl)-2-aminobenzylamine, and characterized. It crystallizes with a distorted square planar structure including two short Co-N bonds (approximate to 1.882 Angstrom) and two short Co-S bonds (approximate to 2.134 Angstrom). The ligand defines an Ii-atom chelate, which may be Co ligands in the mean plane of Go-containing nitrile hydratase. The Co-III oxidation state, reversibly reduced at -1.13 V(vs. SCE) and irreversibly oxidized at +1.29 V (vs. SCE) in DMF, is stable over a 2 V potential range. From the temperature dependence of its magnetic susceptibility, cobalt(III) was found to be in an S = 1 triplet ground state, in agreement with the broad resonances observed in its H-1-NMR spectrum. Preliminary spectral studies showed that this complex does not interact with imidazole, H2O or HO-, but binds two CN- anions or two NO molecules. The IR spectrum of the dinitrosyl complex exhibits two NO stretches at 1765 and 1820 cm(-1), in the range previously observed for dinitrosylated complexes derived from cobalt(I). This result suggests that, similarly to Fe NHases, Co NHases might readily bind NO. (C) 2000 Elsevier Science S.A. All rights reserved.