Studies on QSAR of metalloporphyrin catalysts in the oxidation of cyclohexane to adipic acid

Abstract

The catalysis of chloridized metalloporphyrins in the oxidation of cyclohexane to adipic acid was systematically investigated. The turnover numbers (TON) data of 19 catalysts were obtained experimentally under optimal reaction conditions, and 2.4?10⁶ TON for T(o-Cl)PP-Mn^IIICl catalyst at 2.0?10 ^6 mol/L of dosage was reached under the conditions of dioxygen pressure of 2.5 MPa at 150?C for 4 h. This was the best result reported for this reaction up to now. The QSAR models for each concerned metalloporphyrin were established, where the catalytic activity was significantly correlated with the E_LUMO (the energy level of the lowest unoccupied molecule orbit) and L_M-N (the bond length between metal-nitrogen atoms). Using the QSAR models, four new metalloporphyrins with substituted nitro group were designed, and their catalytic activities were predicted. The experimental TON data of newly designed porphyrins were in good agreement with the predicted ones, and the square of their correlation coefficient was more than 0.958. The above results demonstrated that the proposed structure-activity relationship model could be applied to design some new metalloporphyrin catalysts, and to predict their catalytic activity in cyclohexane oxidation.