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 Co-III complex with two different carboxamido nitrogens and two thiolato sulfur donors

A [Co-III(N2S2)]NEt4 complex, with two carboxamido nitrogens and two alkylt hiolato sulfurs, was prepared from N,N'-(2-thioacetyl-isobutyryl)-2-aminobe nzylamine, and characterized. It crystallizes with a distorted square plana r 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 define s an Ii-atom chelate, which may be Co ligands in the mean plane of Go-conta ining 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 m agnetic susceptibility, cobalt(III) was found to be in an S = 1 triplet gro und state, in agreement with the broad resonances observed in its H-1-NMR s pectrum. Preliminary spectral studies showed that this complex does not int eract with imidazole, H2O or HO-, but binds two CN- anions or two NO molecu les. 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 F e NHases, Co NHases might readily bind NO. (C) 2000 Elsevier Science S.A. A ll rights reserved.