Stabilization of Oxo-Metal Bonding by the π-Conjugated System in Dithiolate Ligands: cis-Dioxotungsten(VI) Bis(naphthalenedithiolato) and the Related Complexes as Models for Tungsten Oxidoreductases

As a model of tungsten oxidoreductase, a dioxotungsten(VI) dithiolato complex, (NEt4)2- [WVIO2(ndt)2]·H2O (1) (ndt = 2,3-naphthalenedithiolato), was synthesized. It has provided the detailed structural dimensions of mutual trans influence between oxo and thiolate. The complex, 1, crystallizes in space group P21/n with a = 7.396(2), b = 17.581(2), c = 28.839(2) Å, β = 95.35(2), and Z = 2, and was refined to R = 2.3%. The short S–C distances of the thiolate trans to the WVI=O groups indicate the presence of the partial double bonding at S–C (thiketone-like) which contributes to the stabilization of the dioxotungsten(VI) species by weakening π-interaction of the WVI–S bonds trans to the WVI=O groups. In the tungstopterin cofactor and the molybdopterin cofactor of the enzyme, the double bonding nature of S–C (thioketone-like) is expected to stabilize the oxo ligand of the tungsten and molybdenum ion.