Dioxotungsten 1,2-benzenedithiolate complex stabilized by NH•••S hydrogen bonds

Novel dioxo-tungsten(VI) bis(1,2-benzenedithiolate) complexes with neighboring amide groups, as models for tungsten enzymes, (NEt4)(2)[(WO2)-O-VI {1,2-S-2- 3,6-(RCONH)(2)C6H2}(2)] (R = CH3, t-Bu), were designed and synthesized. The presence of the NH center dot center dot center dot S hydrogen bond was confirmed through IR spectrometry and X-ray crystallographic analysis. In the (WO2)-O-VI complexes, the NH center dot center dot center dot S hydrogen bond trans to the oxo ligand is stronger than that cis to oxo. On the basis of comparisons with [(WO2)-O-VI(1,2-S2C6H4)(2)](2-), the NH center dot center dot center dot S hydrogen bond positively shifted the W(VI)/W(V) redox potentials and depressed the reduction by benzoin or triphenylphosphine. These results suggest that the NH center dot center dot center dot S hydrogen bond stabilizes the oxo ligand through trans influence and regulates O-atom transfer in tungsten and molybdenum enzymes.