Half‐Sandwich Scorpionate Vanadium, Iron and Copper Complexes: Synthesis and Application in the Catalytic Peroxidative Oxidation of Cyclohexane under Mild Conditions

Abstract

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.

Catalytic Performance of Fe(II)-Scorpionate Complexes towards Cyclohexane Oxidation in Organic, Ionic Liquid and/or Supercritical CO2 Media: A Comparative Study

“…The yield values achieved in acetonitrile were comparable to those previously obtained at room temperature [28] without any added promotor. Higher yields were reported in very different reaction conditions, such as when 1 was supported on carbon nanotubes or zeolites (total yield up to 38%) [32,33] or using microwave (MW) assistance (total yield of 33%) [12,34], always in the presence of pyrazinecarboxylic acid (Hpca) [32][33][34][35].…”

“…The scorpionate complexes 1 [28] and 2 [29] were synthesized and characterized according to methods described in the literature. Liquid CO 2 , purity of 99.995%, in a cylinder with a dip tube was supplied by Air Liquid and used without further purification.…”

“…In addition, the environmentally acceptable oxidant tert-butyl hydroperoxide (TBHP) was used along with a known efficient C-scorpionate Fe(II) catalyst [28] Figure 1a,b, respectively) were selected due to their ability to dissolve large quantities of scCO2, while they themselves are insoluble in scCO2, in accordance with their almost non-existing vapor pressure [30,31]. To our knowledge, this is the first time that the successful use of scCO2 or scCO2-IL as solvents for the oxidation of alkanes catalyzed by a C-scorpionate complex is reported.…”

New Trendy Magnetic C-Scorpionate Iron Catalyst and Its Performance towards Cyclohexane Oxidation

“…The iron(II) complex [FeCl2{κ 3 -HC(pz)3}] (1, pz = pyrazol-1-yl) was synthesized according to a reported procedure [18] and characterized by spectroscopic and analytic techniques.…”

“…The bio-inspired tris(pyrazol-1-yl)methane iron(II) complex [FeCl 2 {κ 3 -HC(pz) 3 }], which was previously proved to act as an efficient catalyst in C-H activation reactions [13][14][15][16][17][18][19][20], was also chosen due to its easy (one-step) synthesis in water at room temperature [18].…”