Compounds [Cp*(2)M(2)O(5)] (M = Mo, 1; W, 2) are efficient pre-catalysts for cyclooctene (COE) epoxidation by aqueous H(2)O(2) in acetonitrile/toluene. The reaction is quantitative, selective and takes place approximately 50 times faster for the W system (k(obs) = 4.32(9)x10(-4) s(-1) at 55 degrees C and 3x10(-3) M concentration for the dinuclear complex, vs. 1.06(7)x10(-5) s(-1) for the Mo system). The rate law is first order in catalyst and COE substrate (k = 0.138(7) M(-1) s(-1) for the W system at 55 degrees C), whereas increasing the concentration of H(2)O(2) slows down the reaction because of an inhibiting effect of the greater amount of water. The activation parameters for the more active W systems (DeltaH(double dagger) = 10.2(6) kcal mol(-1); DeltaS(double dagger) = -32(2) cal mol(-1) K(-1)) were obtained from an Eyring study in the 25-55 degrees C temperature range. The H(2)O(2)urea adduct was less efficient as an oxidant than the aqueous H(2)O(2) solution. Replacement of toluene with diethyl ether did not significantly affect the catalyst efficiency, whereas replacement with THF slowed down the process. The epoxidation of ethylene as a model olefin, catalysed by the [Cp*MO(2)Cl] systems (M = W, Mo) in the presence of H(2)O(2) as oxidant and acetonitrile as solvent, has been investigated by DFT calculations with the use of the conductor-like polarisable continuum model (CPCM). For both metal systems, the rate-limiting step is the transfer of the hydroperoxido O(alpha) atom to the olefin, in accordance with the first-order dependence on the substrate and the zero-order dependence on H(2)O(2) found experimentally in the catalytic data. The activation barrier corresponding to the rate-limiting step is 4 kcal lower for the W complex than for the corresponding Mo analogue (32.3 vs. 28.3 kcal mol(-1)). This result reproduces well the higher catalytic activity of the W species. The different catalytic behaviour between the two systems is rationalised by a natural bond orbital (NBO) study and natural population analyses (NPA). Compared to Mo, the W(VI) centre withdraws more electron density from the sigma bonding [O-O] orbital and favours, as a consequence, the nucleophilic attack of the external olefin on the sigma*[O-O] orbital.

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The oxidation of benzothiophene (BT), dibenzothiophene (DBT) and 4,6dimethyldibenzothiophene (DMDBT) by H2O2 to the corresponding sulfoxides and sulfones has been studied under homogeneous conditions in MeCN with compounds [Cp*2M2O5] (M = Mo, 1; W, 2) as precatalysts. The W system is ca. 100 times more efficient than the Mo analogue, while the relative reactivity of the thiophene substrates is approximately DBT:DMDBT:BT  10:5:1. For all reactions rate constants for both steps (thiophene derivative to sulfoxide, k1; sulfoxide to sulfone, k2) were measured. While k1  k2 for DBT and DMDBT, k1 << k2 for BT, independent of catalyst. Activation parameters for the stepwise oxidations of thiophene derivative to sulfoxide (BT to BTO: H ‡ = 11.4(5) kcal mol -1 and S ‡ = -26.1(1.6) e.u.; DBT to DBTO: H ‡ = 7.7(6) kcal mol -1 and S ‡ = -33(2) e.u.) and sulfoxide to sulfone (BTO to BTO2: H ‡ = 10.8(5) kcal mol -1 and S ‡ = -21.8(1.6) e.u.; DBTO to DBTO2: H ‡ = 10.3(9) kcal mol -1 and S ‡ = -25(3) e.u.) were calculated from variable temperature studies using [Cp*2W2O5]. DFT calculations suggest that the greater reactivity of DBT relative to BT is not caused by ground state effects but rather by a transition state effect associated with the greater thermodynamic gain in DBT oxidation.

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The conversion of amino diols to aminohydroxy acids by oxidation of the primary hydroxy group mediated by homogeneous and heterogeneous TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl radical) is reported. The synthesis uses NaOCl as primary oxidant and TEMPO, either dissolved in the homogeneous phase or entrapped in a sol-gel matrix, as catalytic mediator. Homogeneous TEMPO is suitable for the oxidation of aliphatic methylamino diols, while the hybrid organic-inorganic silica sol-gel catalysts are more selective mediators for the oxidation of benzylic amino diols like the potent antibiotic chloramphenicol which, under homogeneous conditions, are unselectively oxidized to benzoic acids.

The reaction of HTIMP3 (HTIMP3=tris[1-diphenylphosphino)-3-methyl-1H-indol-2-yl]methane) with AgBF4 and Mo(CO)3(NCCH3)3 leads to Ag(HTIMP3)BF4 and Mo(CO)3(HTIMP3), respectively. The metal centre is coordinated to the three phosphorus atoms of the HTIMP3 ligand, which adopts a facial coordination mode, placing a H-Csp3 hydrogen atom at the apical position close to the metal centre. The solid-state structure of Mo(CO)3(HTIMP3) has been determined by X-ray crystallography, and the data have been used as input parameters for obtaining the optimised geometry of the complex using the B3PW91 functional. The silver structure has been modelled from the X-ray parameters of the molybdenum structure. In addition, theoretical calculations on the H-Csp3 downfield shift upon metal coordination has also been performed. They reproduce the experimental H-Csp3 chemical shifts well and supports that proton deshielding is mainly due to the presence of the metal, since the hydrogen is already located in the cone created by the aromatic-phosphino arms in the free ligand.

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{HTIMP 3 = tris[1-(diphenylphosphino)-3-methyl-1H-indol-2-yl]methane} was prepared and fully characterized in both the solid state and in solution. Chloride abstraction by silver cations provides a more reactive compound, [IrH-