Synthesis of polymer catalysts with tailored metalloporphyrin–ligand proximity by precision monomer design

Redox-active enzymes efficiently catalyze a wide range of (bio)chemical reactions using their unique metalloporphyrin catalytic centers that are coordinated with proximal amino acid residues from surrounding polypeptide chains. Chemical synthesis of catalysts that mimic such effective catalytic motifs has long been pursued but remains challenging. Current designs can typically reproduce only selected features of natural enzymes. Here, we present a strategy for synthesizing polymer-supported metalloporphyrin catalysts through the precise design of a norbornene-based monomer bearing a TPP-Co catalytic center and an imidazole axial ligand. This three-in-one strategy enables one-step polymerization to produce a polymer-supported TPP-based catalyst in which a proximal ligand is axially coordinated to the metal center. Spectroscopic characterization revealed the axial-ligand interaction. Compared with the ligand-free polymer P1-Co, which exhibits a Tafel slope of 279 mV dec−1 for the oxygen evolution reaction (OER), the target polymer catalyst P2-Co shows a substantially higher catalytic current, a reduced Tafel slope of 157 mV dec−1, and nearly tenfold higher activity than its monomeric counterpart. This work demonstrates a new strategy for the molecular design of polymer-based, enzyme-mimicking catalysts.