N‐Hydroxyphthalimide Anchored on Diamond Nanoparticles as a Selective Heterogeneous Metal‐free Oxidation Catalyst of Benzylic Hydrocarbons and Cyclic Alkenes by Molecular O₂

Abstract

N‐hydroxyphthalimide (NHPI) derived from trimellitic anhydride has been covalently anchored (4 wt %) through ester bonds to the surface of commercial diamond nanoparticles previously functionalized by chemical and thermal treatments (DH). IR spectroscopy of the NHPI/DH solid shows the presence of a characteristic peak at 1735 cm−1 attributable to the ester bond, while solid‐state MAS 13C NMR spectroscopy shows two broad bands corresponding to carbon atoms of carbonyl groups (167 ppm) and aromatic carbons (127 ppm). NHPI/DH promotes autoxidation of isobutylbenzene involving superoxide (O2.−) and hydroperoxide (HOO⋅) radicals; NHPI/DH can be reused at least three times and reach a minimum turnover number as high as 20 600, which is probably due to the inertness of the diamond surface, allowing free diffusion of reactive oxygen species. Analogous materials in which NHPI was anchored on activated carbon and multiwall carbon nanotubes were inefficient as autoxidation catalysts. NHPI/DH is able to promote also selective aerobic oxidation of other benzylic hydrocarbons and cycloalkenes.

Generating and optimizing the catalytic activity in UiO-66 for aerobic oxidation of alkenes by post-synthetic exchange Ti atoms combined with ligand substitution

“…It is known in the literature that the size of the cycloalkene ring has a strong influence on the product distribution and, particularly, on the ratio between C=C epoxidation versus allylic oxidation that decreases from cyclooctene as the size of the ring decreases. 54,55,76 A similar trend was observed herein (Figure 12). Thus, while for cyclooctene the corresponding epoxide was the only product observed with almost complete selectivity, in the case of cycloheptene formation of the corresponding oxide was accompanied by formation of 2-cycloheptenone with a selectivity that changes as a function of the conversion Figure 12 shows the corresponding time-conversion and conversion-selectivity plots for cycloheptene oxidation using UiO-66(Zr5.4 Ti0.6)-NO2 as catalyst.…”

“…Selective radical quenching experiments were carried out following the general reaction procedure described above, but with the addition of radical quenchers (20 mol% with respect to the substrate). In particular, dimethylsulfoxide (DMSO) [54][55][56][57] or p-benzoquinone 54,55,57,58 were added as selective hydroxyl or superoxide/hydroperoxyl radical scavengers, respectively.…”

“…To gain further insights into the reaction mechanism and, specifically, to obtain some evidence about the nature of the possible reactive oxygen species involved in the cyclooctene oxidation, quenching experiments using p-benzoquinone and DMSO were carried out. p-Benzoquinone is a selective quencher of hydroperoxide/superoxide, 54,55,57,58 while DMSO quenches selectively hydroxyl radicals. [54][55][56][57] Thus, comparison of the performance of the cyclooctene oxidation in the absence and in the presence of quenchers (20 % molar proportion respect to substrate) could provide valuable information on the nature of the active oxygen species responsible for the reaction.…”

Modified Nanocarbons for Catalysis

“…The ND‐based catalyst can be reused at least three times and reached a minimum turnover number as high as 20,600, which was ascribed to the inertness of the diamond surface, allowing free diffusion of reactive oxygen species. In addition, the ND‐based catalyst was able to promote also selective aerobic oxidation of other benzylic hydrocarbons and cycloalkenes . Nanodiamonds and carbon nanohorns (CNHs), among other nanostructured carbon materials (graphene nanoplatelets, graphene oxide, reduced graphene oxide) were used for the immobilization of the C‐scorpionate iron(II) complex [FeCl 2 (Tpm)] [Tpm=κ 3 ‐HC(C 3 H 3 N 2 ) 3 ] in order to get active, selective, and recyclable catalysts for alkane and alcohol oxidations .…”

Catalytic Aerobic Oxidation of C(sp3)−H Bonds

“…NHPI was first used by Masui et al as an electron carrier for the electrochemical oxidation of alcohols [93] and later adopted by Ishii et al for the oxidation of alkanes.While the majority of reactions employing NHPI are in combination with transition metal cocatalysts (e.g.C o, [94] Mn, [95] Cu [96] and Fe [97] )o rh eterogeneous catalysts, [98] also other additives have been used as NHPI activator (e.g. NHPI was first used by Masui et al as an electron carrier for the electrochemical oxidation of alcohols [93] and later adopted by Ishii et al for the oxidation of alkanes.While the majority of reactions employing NHPI are in combination with transition metal cocatalysts (e.g.C o, [94] Mn, [95] Cu [96] and Fe [97] )o rh eterogeneous catalysts, [98] also other additives have been used as NHPI activator (e.g.…”