Robust Mn(iii) N-pyridylporphyrin-based biomimetic catalysts for hydrocarbon oxidations: heterogenization on non-functionalized silica gel versus chloropropyl-functionalized silica gel

Abstract

<p>Simple neutral and cationic Mn porphyrins were immobilized on ordinary chromatographic silica or chloropropyl-functionalized silica supports to yield efficient and reusable biomimetic catalysts for C–H activation and oxyfunctionalization of alkanes.</p>

Iron(III) Complexation with Galactodendritic Porphyrin Species and Hydrocarbons’ Oxidative Transformations

“…The non‐immobilized MnPs showed chemoselectivity toward the carbonyl products. Comparing the results obtained here for the FePs with those reported by Rebouças and co‐workers [41] for the non‐immobilized MnPs, the alcohol global yield are higher, though depending on the solvent used.…”

“…The heterogeneous or homogeneous character of the catalytic process can also affect regioselectivity [41] . In acetonitrile as solvent and after 1 h of reaction (Figure 8a), the regioselectivity is quite similar in both cases: 2‐ol∼3‐ol>4‐ol>1‐ol for FeP2 and 2‐ol∼3‐ol>4‐ol∼1‐ol for FeP3S .…”

“…Thu and co‐workers [40] demonstrated that the use of highly sterically demanding rhodium‐porphyrin catalysts led to selective carbene insertion into a primary C−H bond, with remarkably high selectivity (>80 %) in the reactions with hexane, octane and decane, for example. Rebouças and co‐workers [41] reported the oxidation of heptane using a series of neutral and cationic manganese(III) porphyrins (MnPs) as catalysts and PhIO as oxidant. In this study, the authors observed an inversion in heptane oxidation chemoselectivity after immobilization on the Sil−Cl support if compared to the MnP in solution.…”

Degradation of Dyes Catalyzed by Aminophenyl-Substituted Mn-Porphyrin Immobilized on Chloropropyl Silica Gel and Evaluation of Phytotoxicity

“…MLCT bands occur due to the migration of charges from molecular orbitals higher energy occupied of the metal to the lower energy unoccupied molecular orbitals of the porphyrin. 38 The samples of unmodified silica gel (SiO 2 ) and the functionalized chloropropyl silica gel (Sil-Cl) were derived from our previous study 32 being, thoroughly characterized by elemental analysis (C and Cl), FTIR, thermogravimetric analysis-DTA, 13 C NMR (Sil-Cl), 29 Si NMR (Sil-Cl), specific surface area (Brunauer−Emmett−Teller method), adsorption−desorption isotherms (Sil-Cl), pore size distribution (BJH method, Sil-Cl), scanning electron microscopy (SEM), and transmission electron microscopy, as reported elsewhere. 32 The immobilization of MnP on the functionalized silica gel (Figure 2) occurred via covalent bonding through a nucleophilic substitution of chlorine by the aminophenyl group, generating hydrochloric acid (HCl) as a byproduct.…”

“…38 The samples of unmodified silica gel (SiO 2 ) and the functionalized chloropropyl silica gel (Sil-Cl) were derived from our previous study 32 being, thoroughly characterized by elemental analysis (C and Cl), FTIR, thermogravimetric analysis-DTA, 13 C NMR (Sil-Cl), 29 Si NMR (Sil-Cl), specific surface area (Brunauer−Emmett−Teller method), adsorption−desorption isotherms (Sil-Cl), pore size distribution (BJH method, Sil-Cl), scanning electron microscopy (SEM), and transmission electron microscopy, as reported elsewhere. 32 The immobilization of MnP on the functionalized silica gel (Figure 2) occurred via covalent bonding through a nucleophilic substitution of chlorine by the aminophenyl group, generating hydrochloric acid (HCl) as a byproduct. To neutralize the hydrochloric acid formed in situ, avoiding both the demetalation of MnP and the protonation of the remaining aminophenyl group, triethylamine, a sterically hindered Brønsted-Lowry base, was added in large excess.…”