Heterogenisation of a C‐Scorpionate Fe^II Complex on Carbon Materials for Cyclohexane Oxidation with Hydrogen Peroxide

Abstract

The hydrotris(pyrazol‐1‐yl)methane iron(II) complex [FeCl2{η3‐HC(pz)3}] (pz=pyrazol‐1‐yl) (1) was immobilized on three different carbon materials (activated carbon, carbon xerogel and multi‐walled carbon nanotubes) with three different surface treatments (original, treated with nitric acid, and treated with nitric acid followed by sodium hydroxide) to produce active, selective and recyclable catalysts. The heterogenisation process was more efficient for carbon nanotubes treated with nitric acid and sodium hydroxide. An outstanding improved catalytic performance of complex 1 upon heterogenisation on carbon nanotubes treated with nitric acid and sodium hydroxide (turnover numbers up to 5.6×103 and overall yield of 21 %), relative to the homogeneous system, was achieved for the single‐pot peroxidative oxidation of cyclohexane to the cyclohexanone and cyclohexanol mixture. The heterogenised systems allowed their easy recovery and reuse, at least for five consecutive cycles, maintaining 96 % of the initial activity and concomitant rather high selectivity to cyclohexanol and cyclohexanone.

New Trends in Oxidative Functionalization of Carbon–Hydrogen Bonds: A Review

“…Polynuclear metal complexes containing voluminous organic [63,66,118,119,[129][130][131]186,[213][214][215][216][217][218][234][235][236][237][238][239][240][241] or siloxane [221][222][223][224][225][226][227][228] ligands are also very efficient in oxidations of organic compounds including saturated hydrocarbons with peroxides. For example, dinuclear copper complex 11 [221,224] and hexairon complex 15 (for the structure, see Figure 9) affording the products of cyclohexane oxidation in a very high yield of 46% (see Figure 10 [226]) can be considered as "inorganic models of methane monooxygenases."…”

“…New types of ligands have been proposed in recent decades which form efficient catalysts with transition metal ions. These ligands are: N-heterocyclic carbene (NHC) [202,203], pincer-like [204][205][206][207][208], redox-active ligands [209][210][211][212], and scorpionates [213][214][215][216][217][218].…”

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

“…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].…”

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]. However, for the present study, to compare the catalysts' performances in different media, promotor-free conditions were preferred.…”