Abstract:The new half-sandwich scorpionate complexes [hydridotris(1-pyrazolyl)methane]vanadium trichloride, ([VCl 3 {HC(pz) were synthesized, characterized and shown to act, as well as the related (tripyrazolylmethane)copper dichloride, [CuCl 2 {HC(pz) 3 }] 6, as selective catalysts (or catalyst precursors) for the peroxidative oxidation (with hydrogen peroxide) of cyclohexane to cyclohexanol and cyclohexanone, under mild conditions (at room temperature and using an aqueous solution of H 2 O 2 ). The iron complexes are the most active ones (reaching TON values up to ca. 690), the effects of a variety of factors are reported and the reaction is shown to proceed via both C-and O-centred radical mechanisms, conceivably involving a metal-based oxidant.

Gold(III) complexes of type [AuCl2{eta(2)-RC(R'pz)(3)}]Cl [R = R' = H (1), R = CH2OH, R' = H (2) and R = H, R' = 3,5-Me-2(3), pz = pyrazol-1-yl] were supported on carbon materials (activated carbon, carbon xerogel and carbon nanotubes) and used for the oxidation of cyclohexane to cyclohexanol and cyclohexanone, with aqueous H2O2, under mild conditions.

No abstract

The hydrotris(pyrazol‐1‐yl)methane iron(II) complex [FeCl2{η3‐HC(pz)3}] (pz=pyrazol‐1‐yl) (1) was immobilized on three different carbon materials (activated carbon, carbon xerogel and multi‐walled carbon nanotubes) with three different surface treatments (original, treated with nitric acid, and treated with nitric acid followed by sodium hydroxide) to produce active, selective and recyclable catalysts. The heterogenisation process was more efficient for carbon nanotubes treated with nitric acid and sodium hydroxide. An outstanding improved catalytic performance of complex 1 upon heterogenisation on carbon nanotubes treated with nitric acid and sodium hydroxide (turnover numbers up to 5.6×103 and overall yield of 21 %), relative to the homogeneous system, was achieved for the single‐pot peroxidative oxidation of cyclohexane to the cyclohexanone and cyclohexanol mixture. The heterogenised systems allowed their easy recovery and reuse, at least for five consecutive cycles, maintaining 96 % of the initial activity and concomitant rather high selectivity to cyclohexanol and cyclohexanone.

The reactions of CuII carboxylates (valerate, 2-methylbutyrate, hexanoate, heptanoate) with pyrazole (Hpz) in EtOH or EtOH/water solutions easily afford the triangular trinuclear copper derivatives [Cu3(μ3-OH)(μ-pz)3(RCOO)2(L)x] [R = CH3(CH2)3, L = H2O, x = 1 for 5; R = CH3CH2CH(CH3), L = EtOH, x = 2 for 6; R = CH3(CH2)4, L = EtOH, x = 1 for 7; R = CH3(CH2)5, L = EtOH, x = 1 for 8] as it has been previously found for R = H, L = Hpz, x = 2, (1); R = CH3, L = Hpz, x = 1, (2); R = CH3CH2, L = EtOH, x = 1, (3) and [Cu3(μ3-OH)(μ-pz)3-(CH3(CH2)2COO)2(MeOH)(H2O)], (4). The trinuclear structure common to 5–8 has been assigned on the basis of magnetic susceptibility studies, ESI MS, IR and UV/Vis spectroscopy as well as 1H NMR measurements. The room temp. magnetic susceptibilities of 5–8 almost correspond to the presence of a single unpaired electron for each trinuclear unit. The IR spectra exhibit signals due to the bridging μ3-OH in accordance with what was observed in the spectra of 1–4. Solid-state and MeOH solution UV/Vis spectra show the same features previously reported for 1–4 and 1H NMR spectra of 1–8 show almost identical low field signals that can be assigned to pz– hydrogens. A detailed investigation of the supramolecular structures of 1 and 4 and the single-crystal X-ray study of the polymeric paddlewheel Cu(2-methylbutyrate) 2, A, are also reported. Electrochemical experiments show that in 1–8 the CuII ions can be reduced, in distinct steps, to CuI and Cu0. All the complexes act as catalysts or catalyst precursors for the efficient peroxidative oxidation, by aqueous hydrogen peroxide in acetonitrile and at room temp., of cycloalkanes RH (cyclohexane and cyclopentane) to the corresponding cyclic alcohols and ketones, with overall yields of up to 34% and TONs up to 42. Radical pathways involving the formation of alkyl hydroperoxides (ROOH) are involved

No abstract

The highly efficient eco-friendly synthesis of methanol directly from carbon dioxide and H2 catalysed by the iron(ii) scorpionate catalyst [FeCl2{κ3-HC(pz)3}] is reported.

By reacting copper(II) acrylate with pyrazole (Hpz), two trinuclear copper derivatives [Cu3(mu3-OH)(mu-pz)3(CH2CHCOO)2(H2O)2(Hpz)], 1, and [Cu3(mu3-OH)(mu-pz)3(CH2CHCOO)2(CH3OH)], 2, are obtained, in water and methanol respectively, while copper(II) methacrylate affords [Cu3(mu3-OH)(mu-pz)3(CH2C(CH3)COO)2], 3, independently from the solvent used. In 1 and 2 two triangular trinuclear units are connected through acrylate bridges forming hexanuclear clusters that, in the case of 2 are further connected through double syn-syn carboxylate bridges, generating a 1-D coordination polymer. In the case of 3 a different 1-D coordination polymer is obtained by alternating syn-syn and syn-anti double carboxylate bridges connecting the trinuclear clusters. In all cases H-bonds contribute both to the stabilization of these arrangements and to the formation of more extended supramolecular networks. Compounds 1-3 are valuable catalysts in the peroxidative oxidation with aqueous H2O2, in MeCN at 25 degrees C, of cycloalkanes (i.e. cyclohexane and cyclopentane) to the corresponding ketones and alcohols (overall yield up to 36%, TON = 36), following a radical mechanism as shown by radical trap experiments, and the effects of various factors are studied. Electrochemical experiments show that the copper(II) centres are reduced to copper(I) and copper(0).