Hydrogen activation by high-valent oxo-molybdenum(VI) and -rhenium(VII) and -(V) compounds

The high-valent oxo-molybdenum(VI) and -rhenium(VII) and -(V) derivatives MoO2Cl2, ReCH3O3 (MTO) and ReIO2(PPh3)(2) catalyze the selective hydrogenation of alkynes to alkenes at 80 degrees C under 40 atm of pressure. The reduction of sulfoxides to sulfides has also been performed by oxo-rhenium and -molybdenum complexes using hydrogen as a reducing agent. Activation of hydrogen by MoO2Cl2 and MoO2(S2CNEt2)(2) was shown by means of DFT calculations to proceed by H-H addition to the Mo=O bond, followed by hydride migration to yield a water complex.