Chemometric evaluation of alkane hydroxylation catalyzed by Mn(III) N-alkylpyridylporphyrins immobilized on SiO2

The immobilization of Mn(III) porphyrins (MnPs) on SiO 2 represents a promising strategy for the development of efficient, selective, and recyclable biomimetic catalysts. However, the combined effects of porphyrin structure and immobilization loading on supported biomimetic catalysis remain poorly understood. Herein, four Mn(III) N -alkylpyridylporphyrins (MnTM-2-PyP 5+ , MnTnHex-2-PyP 5+ , MnTM-4-PyP 5+ , and MnTnHex-4-PyP 5+ ) were electrostatically supported on SiO 2 at low scale using various MnP loadings. MnP saturation was achieved around 5 μmol g –1 . A set of eight SiO 2 /MnP materials were prepared in preparative scale with MnP loadings of either 2.5 or 5 μmol g –1 and used as biomimetic catalysts for PhIO-hydroxylation of cyclohexane, as a model reaction. A full two-level, three-factor factorial design (2³ DoE) coupled with multiple linear regression analysis at a significance level of α = 0.05 was employed to evaluate the effects of structural and immobilization parameters on catalytic performance. Product yields of 17-46% (cyclohexanol) and 14-41% (cyclohexanone), and Cy-ol selectivities of 48-63% were achieved. Chemometric analysis revealed strong interactions among MnP isomerism, lipophilicity, and immobilization loading, precluding the independent assessment of these variables. Recycling studies revealed a tradeoff between efficiency and oxidative stability: the SiO 2 /MnTM-2 or 4-PyP 5+ catalysts were simultaneously the most efficient and the most susceptible to oxidative deactivation. The “ ortho effect” was particularly relevant to SiO 2 /MnTnHex-2-PyP 5+ , yielding the most oxidatively stable catalyst, but of limited efficiency. Overall, the interplay among lipophilicity, isomerism, and MnP loading on the SiO 2 /MnP materials simultaneously governs catalytic efficiency and selectivity, representing an effective strategy to fine-tune biomimetic alkane oxidations.