Oxometalates and Dioxygen in Catalytic Oxidation

Vanadium‐Catalysed Aerobic Cleavage of C−C Bonds in Substituted Cyclohexanones To Afford Carboxylic Acids: Two Model Complexes with Tetrahedral Geometry around Vanadium(V)

“…[13,14] Compounds (Ph 3 SiO) 3 VO [15Ϫ19] and [(tBu) 2 Si(O) 2 VOCl] 3 [20] have been structurally characterised. The latter contains a twelvemembered ring, {VOSiO} 3 , in which the vanadium and silicon atoms exist in distorted tetrahedral coordinations. Trisilanols such as R 7 Si 7 O 9 (OH) 3 [R ϭ cyclopentyl, cyclohexyl (cy), phenyl, etc.]…”

“…The latter contains a twelvemembered ring, {VOSiO} 3 , in which the vanadium and silicon atoms exist in distorted tetrahedral coordinations. Trisilanols such as R 7 Si 7 O 9 (OH) 3 [R ϭ cyclopentyl, cyclohexyl (cy), phenyl, etc.] are known to react with VOCl 3 , VO(OnPr) 3 [22] from diphenylsilanediol and vanadium() dialkylamides, VO(NEt 2 ) 3 .…”

“…Vanadium() oxoalkoxides such as [VO(OEt) 3 ] or heteropolyacids containing vanadium() ions with common formula H 3ϩn [PMo 12Ϫn V n O 40 ]·xH 2 O (denoted HPA-n, where n ϭ 1, 2, 3 etc.) have been proposed as precursors for the catalytic oxidation of α-ketols and ketones by dioxygen.…”

“…Moreover, in aerobic ketone oxidations, HPA-n species are active not only as redox systems but also play a very important role as Brønsted acids for the enolisation process. [3,10] To the best of our knowledge there is no iono-covalent crystal structure containing the pervanadyl cation [VO 2 (H 2 O) 4 ] ϩ . In this work we have prepared and characterised two novel dioxovanadium() complexes with two organosilanolato ligands.…”

“…Work on the use of these complexes in homogeneous catalytic systems (oxidation of 2-hydroxycyclohexanone and 2-methylcyclohexanone) with other precursors and comparison of conversions and selectivities with those obtained with HPA-n has made us refine our previous mechanism. [3] The novel fourcoordinate complexes should open perspectives for incorporation of oxovanadium catalysts into polymeric materials. [11] Organosilanols model the hydroxy groups that lie on silica surfaces, [12] and the complexes synthesised can be regarded as models for metal oxides supported on silica surfaces.…”