Novel Scorpionate and Pyrazole Dioxovanadium Complexes, Catalysts for Carboxylation and Peroxidative Oxidation of Alkanes

The dioxovanadium(V) complexes [VO2(3,5‐Me2Hpz)3][BF4] (1) (pz=pyrazolyl), [VO2{SO3C(pz)3}] (2), [VO2{HB(3,5‐Me2pz)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 [...

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Published in:Advanced synthesis & catalysis 2010-01, Vol.352 (1), p.171-187
Main Authors: Silva, Telma F. S., Luzyanin, Konstantin V., Kirillova, Marina V., da Silva, M. Fátima Guedes, Martins, Luísa M. D. R. S., Pombeiro, Armando J. L.
Format: Article
Language:English
Subjects:
alkanes
carboxylation
CH bond activation
oxovanadium complexes
peroxidative oxidation
scorpionate ligands
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Summary:The dioxovanadium(V) complexes [VO2(3,5‐Me2Hpz)3][BF4] (1) (pz=pyrazolyl), [VO2{SO3C(pz)3}] (2), [VO2{HB(3,5‐Me2pz)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‐Me2pz)3] or 3,5‐dimethylpyrazole (3,5‐Me2Hpz; 1), lithium tris(1‐pyrazolyl)methanesulfonate {Li[SO3C(pz)3], 2}, potassium hydrotris(3,5‐dimethyl‐1‐pyrazolyl)borate {K[HB(3,5‐Me2pz)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 η3‐tris(pyrazolyl)borate and η2‐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.
ISSN:1615-4150
1615-4169
DOI:10.1002/adsc.200900660