Behavior of anionic molybdenum(iv, vi) and tungsten(iv, vi) complexes containing bulky hydrophobic dithiolate ligands and intramolecular NH⋯S hydrogen bonds in nonpolar solvents

Abstract

Molybdenum(IV, VI) and tungsten(IV, VI) complexes, (Et₄N)₂[M^IVO{1,2-S₂-3,6-(RCONH)₂C₆H₂}₂] and (Et₄N)₂[M^VIO₂{1,2-S₂-3,6-(RCONH)₂C₆H₂}₂] (M = Mo, W; R = (4-^tBuC₆H₄)₃C), with bulky hydrophobic dithiolate ligands containing NH⋯S hydrogen bonds were synthesized. These complexes are soluble in nonpolar solvents like toluene, which allows the detection of unsymmetrical coordination structures and elusive intermolecular interactions in solution. The ¹H NMR spectra of the complexes in toluene-d₈ revealed an unsymmetrical coordination structure, and proximity of the counterions to the anion moiety was suggested at low temperatures. The oxygen-atom-transfer reaction between the molybdenum(IV) complex and Me₃NO in toluene was considerably accelerated in nonpolar solvents, and this increase was attributed to the favorable access of the substrate to the active center in the hydrophobic environment.