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[WVIO2{1,2-S2-3,6-(RCONH)2C6H2}2] (R = CH3, t-Bu), were designed and synthesized. The presence
of the NH···S hydrogen bond was confirmed through IR spectrometry and X-ray crystallographic analysis. In the
WVIO2 complexes, the NH···S hydrogen bond trans to the oxo ligand is stronger than that cis to oxo. On the basis
of comparisons with [WVIO2(1,2-S2C6H4)2]2-, the NH···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···S
hydrogen bond stabilizes the oxo ligand through trans influence and regulates O-atom transfer in tungsten and
molybdenum enzymes.