Acceptorless Dehydrogenation of Amines using Metal Ligand Cooperative Catalysts

Amrit Singh, Western University

Abstract

Catalytic acceptorless dehydrogenation (AD) is an atom economic route for synthesizing imines and enamines, which are common final or intermediary functionalities in various pharmaceutically relevant molecules and materials. Imines, for example, are present in a wide range of syntheses due to their versatility. Meanwhile, indole is the 9^th most common nitrogen heterocycle in FDA approved drugs. For imine synthesis via AD, selectivity challenges remain. Reactions often afford a product mixture of imine, nitrile, and a secondary amine. Previously, we showed that the metal-ligand cooperative (MLC) catalyst [Ru(Cp)(P^Ph₂N^Bn₂)(MeCN)]PF₆ showed improved selectivity over a non-MLC catalyst. Herein, a broader scope of activity and selectivity assessment for the AD of amines, for a range of [M(Cp)(P^R₂N^R’₂)(MeCN)]PF₆ catalysts will be discussed. [Ru(Cp)(P^R₂N^R’₂)(MeCN)]PF₆ catalysts were explored for the AD of indoline to indole, which revealed that the activity depended on both the R and R’ groups of the P^R₂N^R’₂ ligand. In addition, both ruthenium and iron catalyst derivatives were explored for the AD of benzylamine, which showed that the iron-centered catalyst was highly selective towards the imine product. Investigations into the mechanism will be discussed that reveal connections between catalyst structure and performance.