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

Abstract

A [Co III(N 2S 2)]NEt 4 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 (≈1.882 Å) and two short Co–S bonds (≈2.134 Å). The ligand defines an 11-atom chelate, which may be Co ligands in the mean plane of Co-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 1H-NMR spectrum. Preliminary spectral studies showed that this complex does not interact with imidazole, H 2O 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.