Catalytic Deoxygenation of Nitroarenes Mediated by High-Valent Molybdenum(VI)–NHC Complexes

The high-valent molybdenum(VI) N-heterocyclic carbene complexes, (NHC)MoO2 (1) and (NHC)MoO(NtBu) (2) (NHC = 1,3-bis(3,5-di-tert-butyl-2-phenolato)-benzimidazol-2-ylidene), are investigated toward their catalytic potential in the deoxygenation of nitroarenes. Using pinacol as sacrificial green reductant, both complexes shown to be very active (pre)catalysts for this transformation allowing a reduction catalyst loading down 0.25 mol %. Mechanistic investigations show ?-oxo bridged molybdenum(V) [(NHC)MoO]2O (4) [(NHC)Mo(NtBu)]2O (5) well zwitterionic pinacolate benzimidazolium complex 6, with doubly protonated NHC ligand, potentially species cycle. Both 4 5 can prepared independently by 1 2 using triethyl phosphine (PEt3) or triphenyl (PPh3) were exhibit an unusual multireferenced ground state small singlet–triplet gap at room temperature. Computational studies that spin plays unneglectable role process, efficiently lowering reaction barrier step. details, putting special emphasis on fate will presented routes how nitroarene is facilitated evaluated.