New Strategy for Synthesis of Bis-Pocket Metalloporphyrins Enabling Regioselective Catalytic Oxidation of Alkanes

Cytochrome P450 selectively hydroxylates the ω and ω-1 positions of fatty acids. Among synthetic oxidizing catalysts, Suslick’s bis-pocket porphyrin Mn or Fe complex achieved ω oxidation for the first time, but the yield in the preparation of the catalyst was poor due to steric hindrance, and in addition, the catalyst turnover number in the oxidation reaction was low. We have devised a new synthetic strategy involving the introduction of eight bulky aryl groups at the 2,6-positions of the meso-phenyl groups after construction of the porphyrin skeleton. This strategy greatly improved the yield in synthesis of the catalyst, and a number of derivatives of bis-pocket porphyrin and their metal complexes were prepared. These Ru complexes show unique ω-1 selectivity and provide a much higher turnover number in the oxidation of linear alkane with 2,6-dichloropyridine N-oxide, as compared to the reaction catalyzed by conventional Ru porphyrins.