Abstract
In order to determine the role of the sulfur donors around the Co(III) site of the enzyme nitrile hydratase, we have synthesized a designed ligand PyPSMeH 2 (Hs are dissociable carboxamide hydrogens) with carboxamido nitrogens and thioether sulfur donors. Although Co(III) complexes with bound thioether groups have previously been synthesized with other ligands, attempts to synthesize such a species with PyPSMe 2− have failed. The only complex isolated is the bis complex (Et 4N)[Co(PyPSMe) 2] ( 1) in which the potentially pentadentate PyPSMe 2− ligand acts as tridentate and all four thioether sulfurs remain as pendant groups. In 1, one of the four carboxamido groups is O-bonded. Methylation of the analogous (Et 4N)[Co 2(PyPS) 2] with iodomethane affords (Et 4N)[Co 2(PyPS(SMe)) 2] ( 2), the only Co(III) complex with weakly bound thioether groups. The dimeric complex 2 contains two bridging thiolato sulfurs and each Co(III) center has one bound thioether sulfur in its coordination sphere. These two terminal thioether groups of 2 are replaced easily by other ligands like pyridine. Reaction of CN − with 2 affords the dicyano complex (Et 4N) 2[Co(PyPS(SMe)(CN) 2] ( 3) with pendant thioether group. Collectively, these results indicate that Co(III) centers with coordinated carboxamido nitrogen(s) exhibit very low affinity toward thioether sulfur.
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