Porphyrin-Nanodiamond Hybrid Materials-Active, Stable and Reusable Cyclohexene Oxidation Catalysts

The quest for active, yet "green" non-toxic catalysts is a continuous challenge. In this work, covalently linked hybrid porphyrin-nanodiamonds were prepared via ipso nitro substitution reaction and characterized by X-ray photoelectron spectroscopy (XPS), fluorescence spectroscopy, infrared spectroscopy (IR) and thermogravimetry-differential scanning calorimetry (TG-DSC). The amine-functionalized nanodiamonds (ND@NH2) and 2-nitro-5,10,15,20-tetra(4-trifluoromethylphenyl)porphyrin covalently linked to nanodiamonds (ND@beta NH-TPPpCF(3)) were tested using Allium cepa as a plant model, and showed neither phytotoxicity nor cytotoxicity. The hybrid nanodiamond-copper(II)-porphyrin material ND@beta NH-TPPpCF(3)-Cu(II) was also evaluated as a reusable catalyst in cyclohexene allylic oxidation, and displayed a remarkable turnover number (TON) value of approximate to 265,000, using O-2 as green oxidant, in the total absence of sacrificial additives, which is the highest activity ever reported for said allylic oxidation. Additionally, ND@beta NH-TPPpCF(3)-Cu(II) could be easily separated from the reaction mixture by centrifugation, and reused in three consecutive catalytic cycles without major loss of activity.