A Discrete N,O,N-Supported Gallium Amido Complex for the Intermolecular Hydroamination of Terminal Alkynes

Abstract

The diamino-ether ligand {(C5H9)NH-C6H4}2O (1) was found to readily react with 0.5 equiv of Ga2(NMe2)6 via an amine elimination route to afford the N,O,N-supported Ga amido species {η3-N,O,N-((C5H9)N-C6H4)2O}GaNMe2 (2) in a reasonable yield (51%). As determined by X-ray crystallography, the four-coordinate Ga center in 2 adopts an unusual trigonal-monopyramidal geometry. Compound 2 effectively catalyzes the hydroamination of terminal alkynes (such as 1-hexyne and phenylacetylene) in the presence of primary amines (aniline and butylamine). Kinetic studies on the latter catalytic reactions suggest that these proceed with a first-order rate dependence on alkyne and on species 2. In preliminary studies aiming at the isolation of intermediates relevant to the present catalysis, the dimeric Ga complex [{η2-N,N-((C5H9)N-C6H4)2O}Ga(μ-NHPh)]2 (3) was synthesized by an aminolysis reaction between compound 2 and aniline; its identity was confirmed by X-ray crystallographic analysis.