Enabling the terpyridine ligand motif for Ir-based solid molecular catalysts

Abstract

Terpyridine (tpy) and its derivatives are strongly coordinating ligands with a high degree of customizability. Due to their tendency to form stable bis(tpy) complexes with transition metals such as Ir and Ru, their application in thermal catalysis is limited, instead revolving mostly around electro-, photo- and supramolecular chemistry. Herein, it is demonstrated that immobilization of the tpy motif via incorporation into a polymer suppresses their formation in Ir-catalyzed formic acid dehydrogenation (FADH), highlighting a distinct advantage of solid molecular catalysts (SMCs). A catalytic activity of up to 175 000 h⁻¹ was achieved at 160 °C and maintained at temperatures as low as 80 °C. Based on the results of a kinetic isotope effect (KIE) study, a catalytic cycle is proposed and the rate-determining step is identified. In a continuous setup, the most active SMC retained its activity over the course of 5 days, resulting in a TON upwards of 2 800 000. Through XPS, HAADF-STEM (-EDX) and EXAFS analyses, insights into the interaction between a metal precursor and poly-terpyridine are gained.