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The novel complex W (=O)Np 3 F has been prepared by fluorination of the corresponding chloride counterpart with AgBF 4 . The reactivity of this complex with silica dehydroxylated at 700 °C afforded a well-defined silica supported monopodal tungsten oxo trialkyl surface species (≡SiO)W (=O)Np 3 . The reaction proceeds both through silanolysis of the W-F bond and opening of a siloxane bridge, with formation of a Si-F fragment, thanks to the affinity of silicon for fluoride. The resulting surface species was characterized by elemental analysis, DRIFT, solid state NMR and EXAFS spectroscopy. This material presenting fluorine on its surface shows an enhanced catalytic activity in propylene self-metathesis compared to its monopodal counterpart (≡SiO)W (=O)Np 3 (prepared from W (=O)Np 3 Cl) suggesting that the Si-F in a close vicinity to the W decreases the electron density of the W and thus increases its reactivity towards the olefinic substrate. [ABSTRACT FROM AUTHOR]

Abstract: Mixed μ-phosphido or μ-thiolato μ-halo-dimolybdenum(III) compounds [Mo2Cp2(μ-SMe)2(μ-X)(μ-Y)] (X=PPh2, Y=Cl (1); X=SCH3, Y=Br (3), I(4)) have been studied. Syntheses and X-ray structures of the new bromo and iodo analogues of [Mo2Cp2(μ-SMe)3(μ-Cl)] (2) are reported. While preparing 3 a side-product 5 was obtained and structurally characterised as the Mo5 system [{Mo2Cp2Br(μ-O)(μ-SMe)2}2(μ-MoO4)], containing a {MoIV–MoIV–O–(MoVIO2)–O–MoIV–MoIV} unit. The influence of the bridging groups on the structures and electrochemical behaviour of the complexes [Mo2Cp2(μ-SMe)2(μ-X)(μ-Y)] 1–4 has been investigated. In MeCN–[NBu4][PF6] the first oxidation of [Mo2Cp2(μ-SMe)2(μ-PPh2)(μ-Cl)] (1) is quasi-reversible, contrasting with the essentially irreversible first oxidation of the thiolate analogue [Mo2Cp2(μ-SMe)3(μ-Cl)] (2) under similar conditions. The effects of lowering the temperature or increasing the scan rate on the oxidation of 1 were examined: the initial quasi-reversible oxidation at first became irreversible but at still higher scan rates or lower temperatures the oxidation was again quasi-reversible. This suggests that the oxidation of 1 in MeCN is followed by reversible coordination of acetonitrile to afford the species [Mo2Cp2(μ-SMe)2(μ-PPh2)(Cl)(MeCN)]+ (7 +). Cyclic voltammetry of [Mo2Cp2(μ-SMe)3(μ-Y)](Y=Br (3) or I (4)) showed two quasi-reversible diffusion-controlled oxidation steps in CH2Cl2–[NBu4][PF6] or thf–[NBu4][PF6]. In acetonitrile, the fast loss of the halide ligands results in the formation of [Mo2Cp2(μ-SMe)3(MeCN)2]+ species. [Copyright &y& Elsevier]

Abstract: A dichloro oxovanadium(V) alkoxide complex [VOCl2(OCH2CH2OCH2CH2O n Bu)] was synthesised by reaction of VOCl3 and 2-(2-butoxyethoxy)ethanol in pentane. It was characterised by IR, 1H, 13C and 51V NMR spectroscopy, mass spectrometry and elemental analysis. Single-crystal X-ray diffraction reveals a monomeric complex with all oxygen atoms of the ligand attached to the overall octahedrally coordinated vanadium atom. This complex exhibits remarkably higher activity than VOCl3 towards ethene polymerisation with diethyl aluminium chloride as co-catalyst and methyl trichloroacetate as promoter. The complex also catalyses the epoxidation of cyclooctene to cyclooctene oxide with tert-butyl hydroperoxide. [Copyright &y& Elsevier]