Photoredox reactions of oxomolybdenum(V) with phosphines

The fluorescent molybdenum(V)-oxo complex MoOCl4(H2O)(-), and oxomolybdenum(V)-phosphine complexes derived from it, undergo thermal and photochemical reactions in acetonitrile with the series of phosphines PEt3, PEt2Ph, PEtPh2, and PPh3. PEt3 reacts spontaneously to form several products: crystalline (PPh4)[(MoCl4)-Cl-III(PEt3)(2)] and (PPh4)(2)[(MoOCl5)-O-V]. 2CH(2)Cl(2); and a maroon oil that contains OPEt3, (MoOCl2)-O-IV(PEt3)(2) and (MoCl4)-Cl-IV(PEt3)(2). The Mo(III) and OPEt3 products show that oxygen atom transfer has occurred. PEt2Ph and PEtPh2 show no significant redox activity with oxomolybdenum(V) in the dark, but irradiation (lambda > 320 nm, CH3CN solution) leads to reduction of Mo(V) and production of the corresponding phosphine oxides. The molybdenum(III) product, cis-mer-MoCl3(OPEt2Ph)(2)(PEt2Ph), was isolated from the PEt2Ph experiment. PPh3 is not oxidized under these conditions; instead, spectral evidence suggests that photoinduced ligand substitution occurs, producing MoOCl3(PPh3)(2). Selective irradiation of the longer-wavelength Mo(V) absorption bands leads to similar photoredox reactions, but much more slowly. X-ray analyses of two reaction products, (PPh4)(2)[(MoOCl5)-O-V]. 2CH(2)Cl(2) and cis-mer-(MoCl3)-Cl-III(OPEt2Ph)(2)(PEt2Ph), an reported. (C) 2000 Elsevier Science Ltd. All rights reserved.