Loading...
2 results
Search Results
Now showing 1 - 2 of 2
- Novel Scorpionate and Pyrazole Dioxovanadium Complexes, Catalysts for Carboxylation and Peroxidative Oxidation of AlkanesPublication . Silva, Telma F. S.; Luzyanin, Konstantin V.; Kirillova, Marina V.; Guedes Da Silva, M. Fátima C.; Martins, Luisa; Pombeiro, ArmandoThe dioxovanadium(V) complexes [VO2(3,5-Me(2)Hpz)(3)][BF4] (1) (pz = pyrazolyl), [VO2{SO3C(pz)(3)}] (2), [VO2{HB(3,5-Me(2)pz)(3)}] (3) and [VO2{HC(pz)(3)}][BF4] (4), bearing pyrazole or scorpionate ligands, were obtained by reaction of triethyl vanadate [VO(OEt)(3)] with hydrotris(3,5-dimethyl-1-pyrazolyl)methane [HC(3,5-Me(2)pz)(3)] or 3,5-dimethylpyrazole (3,5-Me(2)Hpz; 1), lithium tris(1-pyrazolyl)methanesulfonate {Li[SO3C(pz)(3)], 2}, potassium hydrotris(3,5-dimethyl-1-pyrazolyl)borate {K[HB(3,5-Me(2)pz)(3)], 3} and hydrotris(1-pyrazolyl)methane [HC(pz)(3), 4], respectively. Treatment of [VO(OEt)(3)] with potassium hydrotris(1-pyrazolyl)borate {K[HB(pz)(3)]} led to the mixed eta(3)-tris(pyrazolyl)borate and eta(2)-bis(pyrazolyl)borate oxovanadium(IV) complex [VO{HB(pz)(3)}{H2B(pz)(2)}, 5]. The compounds were characterized by elemental analyses, IR, NMR and EPR spectroscopy, FAB and ESI mass spectrometry, cyclic voltammetry and, for 5, also by single crystal X-ray diffraction analysis. All complexes exhibit catalytic activity in the single-pot carboxylation [in trifluoroacetic acid/potassium peroxodisulfate (CF3COOH/K2S2O8)] of gaseous alkanes (methane and ethane) to carboxylic acids (yields up to 40%. TONs up to 157) and in the peroxidative oxidation [in water/acetonitrile (H2O/NCMe)] of liquid alkanes (cyclohexane and cyclopentane) to the corresponding alcohols and ketones (yields up to 24%, TONs up to 117), under mild conditions.
- Pyrazole and trispyrazolylmethane rhenium complexes as catalysts for ethane and cyclohexane oxidationsPublication . Alegria, Elisabete; Kirillova, Marina V.; Martins, Luisa; Pombeiro, ArmandoThe pyrazole complexes [ReCl2{N2C(O)Ph}(Hpz)(PPh3)2] 2 (Hpz = pyrazole), [ReCl2{N2C(O)Ph}(Hpz)2(PPh3)] 3 and [ReClF{N2C(O)Ph}(Hpz)2(PPh3)] 4, and the tris(pyrazolyl)methane compounds [ReCl2(HCpz3)(PPh3)][BF4] 5 (pz = pyrazolyl), [ReCl3{HC(pz)3}] 7, [ReOCl2{SO3C(pz)3}(PPh3)] 8 and [ReO3{SO3C(pz)3}] 9, and their precursors [ReCl2{η2-N,O-N2C(O)Ph}(PPh3)2] 1 and [ReOCl3(PPh3)2] 6, act as selective catalysts (or catalyst precursors), in a single-pot process, for the oxidation of ethane, in the presence of potassium peroxodisulfate K2S2O8, in trifluoroacetic acid (TFA), to give acetic acid, in a remarkable yield (up to ca. 40%) and under mild conditions (in some cases carboxylation can also occur to give propionic acid, but in a much lower yield). The catalytic peroxidative oxidation of ethane to acetaldehyde and of cyclohexane to cyclohexanone and cyclohexanol by an aqueous solution of H2O2 at room temperature is also achieved by using most of those catalyst precursors. The effects of a variety of factors were studied towards the optimization of the processes which are shown to proceed via both C-centered and O-centered radical mechanisms.