Room-Temperature Intermolecular Hydroamination of Vinylarenes Catalyzed by Alkali-Metal Ferrate Complexes

Abstract

Alkene hydroamination of multiple bonds represents a valuable and atom-economical approach to accessing amines, using simple and widely available starting materials. This reaction requires a metal catalyst, and despite the success of noble transition metals, s-block, or f-block elements, iron organometallic complexes have found limited applications. Partnering iron with an alkali metal and switching on bimetallic cooperativity, we report the synthesis and characterization of a series of highly reactive alkali-metal alkyl ferrate complexes, which can deprotonate amines and activate them toward the catalytic hydroamination of vinylarenes. An alkali-metal effect has been observed, with the sodium analogue being the best for an efficient hydroamination of different styrene derivatives and amines. Stoichiometric studies on the reaction of the sodium tris(alkyl) ferrate complex with 3 mol equiv of piperidine evidenced the ability of the three alkyl groups on Fe to undergo amine metalation, furnishing a novel tris(amido) sodium ferrate which is postulated as a key intermediate in these catalytic transformations. The enhanced reactivity of these alkali-metal ferrates contrasts sharply with that of the Fe(II) bis(alkyl) precursor which is completely inert toward alkene hydroamination.