Metallo-Deuteroporphyrin as a Biomimetic Catalyst for the Catalytic Oxidation of Lignin to Aromatics

A series of metallo-deuteroporphyrins derived from hemin were prepared as models of the cytochrome P450 enzyme. With the aid of the highly active Co^II deuteroporphyrin complex, the catalytic oxidation system was applied for the oxidation of several lignin model compounds, and high yields of monomeric products were obtained under mild reaction conditions. It was found that the modified cobalt deuteroporphyrin that has no substituents at the meso sites but does have the disulfide linkage in the propionate side chains at the β sites exhibited much higher activity and stability than the synthetic tetraphenylporphyrin. The changes in the propionate side chains can divert the reactivity of cobalt deuteroporphyrins from the typical C-C bond cleavage to C-O bond cleavage. Furthermore, this novel oxidative system can convert enzymolysis lignin into depolymerized products including a significant portion of well-defined aromatic monomers.