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

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.