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

The dioxovanadium(V) complexes [VO 2 (3,5‐Me 2 Hpz) 3 ][BF 4 ] ( 1 ) (pz=pyrazolyl), [VO 2 {SO 3 C(pz) 3 }] ( 2 ), [VO 2 {HB(3,5‐Me 2 pz) 3 }] ( 3 ) and [VO 2 {HC(pz) 3 }][BF 4 ] ( 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[SO 3 C(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 η 3 ‐tris(pyrazolyl)borate and η 2 ‐bis(pyrazolyl)borate oxovanadium(IV) complex [VO{HB(pz) 3 }{H 2 B(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 (CF 3 COOH/K 2 S 2 O 8 )] 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 (H 2 O/NCMe)] of liquid alkanes (cyclohexane and cyclopentane) to the corresponding alcohols and ketones (yields up to 24%, TONs up to 117), under mild conditions.