Energy catalysis needs ligands with high oxidative stability
Agnes E. Thorarinsdottir, Daniel G. Nocera
Abstract
Heterogeneous catalysts predominate in large-scale and technologically important processes because of their privileged stability under harsh operating conditions. Despite this notable performance advantage, they lack the tunability and control of reaction mechanism offered by molecular catalysts, which are particularly predisposed to rational design with ligand modification. A 70-year research effort in molecular catalysis has largely focused on reductive catalytic transformations (e.g., hydrogenation, metathesis, C–H activation/functionalization, cross-coupling bond formation, Ziegler-Natta polymerization) and consequently attendant ligand designs (e.g., amines, amides, phosphines, polycyclic/heterocyclic aromatics and macrocycles, (iso)nitriles) show poor stability outside a reducing environment. Oxidative instability of ligands has been particularly problematic for energy-conversion catalysis, as any large-scale renewable fuels cycle relies on the extraction of electrons and protons from water. The typical ligands of organometallic catalysis are ill suited to withstand the harsh oxidizing conditions of oxygen evolution reaction, providing an imperative for research directed toward designing oxidatively and hydrolytically stable ligands.