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

Abstract

The diamino-ether ligand {(C 5 H 9 )NH-C 6 H 4 } 2 O (1) was found to readily react with 0.5 equiv of Ga 2 (NMe 2 ) 6 via an amine elimination route to afford the N,O,N-supported Ga amido species {η 3 -N,O,N-((C 5 H 9 )N-C 6 H 4 ) 2 O}GaNMe 2 (2) in a reasonable yield (51%). As determined by X-ray crystallography, the four-coordinate Ga center in 2 adopts an unusual trigonalmonopyramidal 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 [{η 2 -N,N-((C 5 H 9 )N-C 6 H 4 ) 2 O}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.

Applications and reactivity trends of homoleptic p-block metal amido reagents

“…The reaction of Ga(NMe 2 ) 3 with a diamino-ether ligand {(C 5 H 9 )NH-C 6 H 4 } 2 O (5H 2 ) proceeded with double deprotonation of 5H 2 with elimination of Me 2 NH affording monomeric (5)GaNMe 2 which could catalyse the intermolecular hydroamination of terminal alkynes by primary amines. 120 The equivalent aluminium analogues (5) AlNMe 2 however showed no reactivity. 120…”

Gallium and Indium Compounds in Homogeneous Catalysis

“…34,35 (28, inset), prepared by an amine elimination reaction between the diamino-ether ligand precursor and [Ga 2 (NMe 2 ) 6 ], catalyzes the hydroamination of various terminal alkynes with aniline or butylamine to yield Markovnikov-type products (28). 36 Such complex is much more effective than [Ga 2 (NMe 2 ) 6 ], which was attributed to a ligand-imposed constrained geometry in (N,O,N)Ga amido species resulting into an enhanced Lewis acidity at Ga(III). 37 It is thought that the catalysis occurs via an initial reaction of the amine substrate with the Ga(III) precursor to generate a gallium amido species that would act as the actual catalyst.…”

“…Alkene Epoxidation Gallium-catalyzed alkene epoxidation was investigated using polyamine-supported [(N x ) y GaCl 2 ]Cl (x = 2; y = 2 and x = 4, 5, 6; y = 1) cationic complexes (36), readily accessible by reaction of the neutral polydentate amine ligands with GaCl 3 , in the presence of peracetic acid (PAA R ). The use of phenanthroline (phen) ligands led to the highest catalytic activities with the selective formation of the epoxide product.…”

Ruthenium(II) Complexes with Chelating N-Heterocyclic Carbenes and a Ruthenate(II) Complex as Catalysts for the Anti-Markovnikov Hydroaminations of Styrene

“…To date, a wide variety of metal-based catalysts, including complexes of main group metals, lanthanides, and transition metals, as well as strong bases, and Lewis and Brønsted acids have been developed in these fields. [35][36][37][38] Hydroamination proceeds through addition of N-H bond across C-C multiple bond via either inter-or intramolecularly to product the target amine, the addition of N-H is regioselective, and it follows the Markovnikov or anti-Markovnikov rule. [39][40][41][42][43][44] The regioselectivity control is vital in hydroamination reactions and anti-Markovnikov hydroamination is a great challange.…”