Significant differences of monooxotungsten(iv) and dioxotungsten(vi) benzenedithiolates containing two intramolecular NH⋯S hydrogen bonds from molybdenum analogues

Abstract

A monooxotungsten(IV) benzenedithiolate complex containing two intramolecular NH⋯S hydrogen bonds, (NEt₄)₂[W^IVO(1,2-S₂-3-t-BuNHCOC₆H₃)₂] (1-W), was synthesized via a ligand-exchange reaction between a new starting complex, (NEt₄)₂[W^IVO(SC₆F₅)₄], and a partially deprotonated dithiol. When dithiol was used in solution, the oxo ligand was protonated and removed to afford (NEt₄)₂[W^IV(1,2-S₂-3-t-BuNHCOC₆H₃)₃]. The trans isomer, trans-1-W, was crystallized, and the molecular structure was determined via X-ray analysis. Trans-1-W was gradually isomerized by heating it in solution and it eventually achieved an approximately 1 : 1 mixture of trans/cis isomers after 48 days. However, a slightly excess amount of trans isomer remained, so the isomerization rate was considerably slower than that of the molybdenum analogue. In the presence of NEt₄BH₄, deuteration of the NH protons was observed in acetonitrile-d₃. The oxidation of both trans- and cis-1-W by Me₃NO afforded the corresponding dioxotungsten(VI) complex, (NEt₄)₂[W^VIO₂(1,2-S₂-3-t-BuNHCOC₆H₃)₂] (2-W), as a single isomer. The contributions of the NH⋯S hydrogen bonds to the bond distances, vibrational data, and electrochemical properties are described via comparisons with their molybdenum analogues. The results of this comparative study yielded insights into both tungsten and molybdenum enzymes.