DFT Study on the Interaction of Tris(benzene-1,2-dithiolato)­molybdenum Complex with Water. A Hydrolysis Mechanism Involving a Feasible Seven-Coordinate Aquomolybdenum Intermediate

In the present work, the reactivity of the tris­(benzene-1,2-dithiolato)­molybdenum complex ([Mo­(bdt)₃]) toward water is studied by means of the density functional theory (DFT). DFT calculations were performed using the M06, B3P86, and B3PW91 hybrid functionals for comparison purposes. The M06 method was employed to elucidate the reaction pathway, relative stability of the intermediate products, nature of the Mo–S bond cleavage, and electronic structure of the involved molybdenum species. This functional was also used to study the transference of electrons from the molybdenum center toward the ligands. The reaction pathway confirms that [Mo­(bdt)₃] undergoes hydrolysis, yielding dihydroxo-bis­(benzene-1,2-dithiolato)­molybdenum complex ([Mo­(OH)₂(bdt)₂]) and benzenedithiol. The reaction takes place through seven transition structures, one of them involving an aquo seven-coordinate molybdenum intermediate stabilized by a lone pair (LP) LP_O→LP_Mo hyperconjugative interaction. This heptacoordinate species allows understanding of the observed oxygen atom exchange between water and tertiary phosphines mediated by these complexes. Calculations also show that [Mo­(C₂H₄S₂)₃] and [Mo­(OH)₂(C₂H₄S₂)₂] have d² and d⁰ electronic configuration, and hence an electron pair must be transferred during the course of the hydrolysis. The frontier molecular orbital (FMO) analysis concludes that the electron pair is transferred in the rupture of the second Mo–S bond, from the occupied donating Mo d_{<i>x</i>²–<i>y</i>²} orbital to the unoccupied C₂H₄(SH)₂ S–C σ* ligand orbital. This result is supported by the bond dissociation energy calculations, which demonstrate that the neutral dissociation of the second Mo–S bond is energetically the more favorable