Abstract
Oxidation of [WC^-CsHsMOCHaXCHs)] (1) with ferrocenium hexafluorophosphate in methyl ethyl ketone at room temperature leads to a 76% yield of the W(V) oxo complex [{W(?/5- CeHsMCHslhCti-O)]2"1" (22+), established by a single-crystal X-ray diffraction study of the PF6“ salt to contain two d1 [W^-CsHsMCHs)]24" moieties connected by a linear oxo bridge such that the W atoms, the bridging oxygen atom, and the methyl groups are coplanar with an anti orientation of the methyl groups. The molecule is diamagnetic in the solid state and in solution, implying spin pairing of the metal centers through a -interaction involving the oxo bridge, and exhibits a strong absorption in the visible region (Amax 525 nm, e = 23 600 L molTM1 cmTM1) assigned to a transition with some MLCT character from a nonbonding level formed by the -interaction to an empty antibonding level with * character. The oxo-bridged dimer 22+ is photosensitive and photodisproportionates in CH3CN to give the d° terminal oxo complex [W^-CsHsMOXCHs)^ (3+) and the d2 solvent-trapped methyl complex [W(?/5- C5H5MNCCH3XCH3)]"1" (4+). The W(IV) acetonitrile complex 4+ has been independently isolated and characterized following protolysis of [WC^-CsHsMCHs^] (7) with NH4PF6 in CH3CN. The W(VI) oxo complex [WC^-CsHsMOXCHsXlPFe (3[PF6]) has been prepared in 74% yield by photolysis of 4[PFe] in acetone under O2. An X-ray diffraction study of the ITM salt 3[I] has established that 3+ is a terminal oxo complex. The oxo complex is not formed in the absence of O2, even when 4[PF6] is heated in the presence of water, and it is proposed that 3+ is formed via addition of 62 to transient “[W^-CsHsMCHs)]TM” to form the reactive peroxo intermediate [WC^-CsHsMCHsX^-Cyr. Photolysis of 2[PF6] in the weakly coordi- nating solvent acetone under O2 results in clean conversion to 3+ by a sequence presumed to involve photodisproportionation of 22+ to give some 3+ directly, together with “[ ( °- C5H5)2(CH3)]+”, which is then oxidized to 3+. Ferrocenium oxidation of 1 in CH2CI2 results in formation of the radical cation [W^-CsHsMCHslCl]"1", independently prepared and characterized as a PFeTM salt by ferrocenium oxidation of [W(^5-C5H5)2(CH3)C1], which is in turned by protolysis of 7 with NH4 C1.