Photoredox reactions of oxomolybdenum(V) with phosphines

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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)[Mo(III)Cl4(PEt3)2] and (PPh4)2[Mo(V)OCl5]·2CH2Cl2; and a maroon oil that contains OPEt3, Mo(IV)OCl2(PEt3)3 and Mo(IV)Cl4(PEt3)2. The Mo(III) and OPt3 products show that oxygen atom transfer has occurred. PEt2Ph and PEtPh2 show no significant redox activity with oxomolybdenum(V) in the dark, but irradiation (λ > 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[Mo(V)OCl5]·2CH2Cl2 and cis-mer-Mo(III)Cl3(OPEt2Ph)2(PEt2Ph), are reported. (C) 2000 Elsevier Science Ltd.

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