Metal Ligand Cooperative Complexes for Acceptorless Dehydrogenation of Amines

Matthew D. Hoffman, The University of Western Ontario

Abstract

Complexes of the type [M(Cp/Cp*)(MeCN)(P^R₂N^R′₂)]PF₆ (M = Fe, Ru) were synthesized and/or tested towards acceptorless dehydrogenation (AD) of amines. The primary amine benzylamine can undergo AD to form a mixture of products, and a selection of catalysts were employed in an attempt to control product selectivity. As a result, trends in product distribution were observed by modifying the primary and secondary coordination spheres on the catalyst. A new complex, [Fe(Cp)(MeCN)(P^Ph₂N^Ph₂)]PF₆ (3a) was synthesized and characterized and was found to be a completely selective dehydrogenation catalyst. This is the first example of an iron catalyst capable of selective dehydrogenation without the need for an exogenous base. Mechanistic analysis was conducted using in-situ IR spectroscopy to elucidate the reaction rate order, and rate-determining step for [Ru(Cp)(MeCN)(P^Ph₂N^Ph₂)]PF₆ (1a) using indoline. The results of these mechanistic studies suggest that the catalytic mechanism for 1a is a cooperative outer sphere mechanism.