The mechanism and origins of the chemo- and regio-selectivity of ruthenium porphyrin catalyzed C-H bonds oxidation

Selective functionalization of polymers derived from branched alkane monomers is extremely challenging due to the low reactivity of C - H bonds and uncontrolled depolymerization. In this work, the chemoselective and regioselective catalytic oxygenation mechanism of hydrocarbons with ruthenium porphyrin complexes and aromatic N -oxides was investigated by density functional theory (DFT) calculations. The results revealed that the oxoruthenium porphyrin species with remarkable reactivity as oxygen transfer agents is responsible for the hydrogen abstraction from C - H bonds followed by fast hydroxyl radical rebound. Details regarding the calculations of various oxidation processes show that the regioselectivity is related to the intrinsic strength of different C - H bonds in branched alkanes and the charge transfer of the hydrogen atom transfer (HAT) step. Comparing the oxidations of branched alkanes to alcohols and ketones, the chemoselectivity is attributed to the relative barriers of HAT pathways in the two-step oxidation stage. Finally, the substituent effects of fluorine in the porphyrin ligand are elucidated and a stronger electron -withdrawing group is predicted to promote the HAT process and regulate hydroxyl radical rebound, ultimately enabling more efficient oxidation. These findings provide relevant information for understanding the selective oxidation of polyolefins through transition metal catalysis and enzymatic catalysis.