Novel mono(dithiolato) molybdenum(VI) and tungsten(VI) complexes were isolated through the searching for potential active species in the catalytic air oxidation of benzoin by [Mo(V)O(SR) ] complexes. Among these, (NEt ) [{Mo(VI)O (3-triphenylsilyl-1,2-benzenedithiolato)} (μ-O)] · 2DMF (1), (PPh ) [{W(VI)O (1,2-benzenedithiolato)} (μ-O)] (3), and (NEt ) [{W(VI)O (2,3-naphthalenedithiolato)}2(μ-O)] (5) were structurally characterized by X-ray crystallography. The electrochemical, electronic, as well as Raman/IR spectral properties of the tungsten complexes, 3 and 5, have been investigated and compared with the corresponding bis(dithiolato) complexes, e.g. [W(VI)O (dithiolato) ] . The μ-oxo-binuclear species, [{Mo(VI)O (SR) } (μ-O)] , is proposed as a possible active species for the catalytic air oxidation of benzoin by the Mo(V) thiolato complexes. 4 4 2 2 2 4 2 2 2 4 2 2 2 2 2 2 2 - 2- 2-