Towards Incorporating Iridium Pincer Complexes into Polymeric Scaffolds For Site-Isolated Alkane Dehydrogenation Catalysis

Abstract

Alkanes remain a difficult resource to harness through chemical transformation. Iridium pincer complexes can catalyze alkane dehydrogenation at elevated temperatures (generally > 180 °C) and display high thermal stability and modularity. Based on precedent with zeolite and micellar materials for other catalytic reactions, we hypothesize that incorporating an iridium complex into a macromolecular framework will lead to catalysts with increased stability, compatibility, and reactivity and will overcome several limitations of the iridium-catalyzed reaction, namely the need for high catalyst loading and high reaction temperatures as well as the poor long-term stability of the catalyst. To that end, two small molecule iridium POCOP pincer complexes were synthesized as benchmarking complexes. Synthesis of a vinyl-appended analogue for direct polymerization into a polymer chain is also underway. To explore the effects of polymeric scaffolding for catalyst isolation and enhancement, our initial target is a linear polystyrene structure, though we intend to use more complicated polymer architectures in the future. Deprotection issues during the synthesis of the vinyl-appended analogue inspired the polymerization of poly(styrene-co-protected diol) copolymer. This copolymer can serve as one of four possible routes to the desired polymeric system. The iridium systems can be studied as alkane dehydrogenation catalysts using a range of temperatures and concentrations to examine their reactivity under various conditions.