Interaction of Multiple Bonds with NacNacGa: Oxidative Cleavage vs Coupling and Cyclization

Abstract

The reactivity of the gallium(I) compound NacNacGa (4) to a variety of unsaturated compounds has been studied. Whereas 4 proved surprisingly unreactive toward olefins, ketones, guanidines, and thioureas, it reacts with isocyanates and carbodiimides to furnish the products of coupling of two heterocumulenes. With isothiocyanate, the CS cleavage occurs, leading to the dimer (NacNacGa) 2 (μ-S)(μ-CNPh) and the cyclization product NacNacGa(S 2 CNPh). These compounds were characterized by multinuclear NMR spectroscopy and X-ray crystal structure analyses. Oxidative addition of SPPh 3 occurs at elevated temperatures and results in the known dimer [NacNacGa(μ-S)] 2 .

Selective Cross‐Coupling of Unsaturated Substrates on AlI

“…The identity of 5 was assigned on the basis of NMR spectroscopy and by comparison with the relatedc ompound 4,w hose molecular structure wasf ully elucidated by X-ray crystallogra-phy.T he salient features of the 1 HNMR spectrum of 5 in C 6 D 6 are the presence of ad earomatized pyridine ring and am ethine signal at 4.96 ppm assigned to the uniquep roton at the 2-position of the pyridine ring that correlates with a 13 CNMR signal at 82.9 ppm of the former carbonyl group. The connectivity of this compound was further confirmed by X-ray diffraction analysis.…”

“…[11] Hill et al reported the related homocoupling of two benzophenones on am agnesium boryl compound 2. [12] Our interesti nt his area was mo-tivated by two separate observations:W eo bservedc oupling of isocyanates and diimides on the Ga I compound NacNac-Ga, [13] and secondly, we discovered sequential coupling of the isolable benzophenone adduct NacNacAl(h 2 (O,C)-OCPh 2 )( 3) with unsaturated substrates that include carbonyls, imines,n itriles, and even heterocycles, (Scheme 1d). [14] These findings posed the questionast owhether the chemoselectivec oupling of two different unsaturated molecules on am ain-group center could be possible.…”

Sequential Oxidation and C−H Bond Activation at a Gallium(I) Center

“…Intrigued by the ease of these C−H activations, we decided to check the generality of this oxidation/C−H activation reaction. We previously established that 10 is amenable to bond cleavage and cyclization of heterocumulenes (S=C=NR, O=C=NR, CO 2 , CS 2 ) and α,β‐enones, but does not react with nonconjugated C=O, P=O, and S=O bonds . For the latter class of substrates, the C−H activation can be easily investigated by direct N 2 O oxidation of mixtures of 10 and substrates.…”

The unique β-diketiminate ligand in aluminum(i) and gallium(i) chemistry

“…1,3-Di-p-tolylcarbodiimide and Dipp NacNacGa(I) formed the coupling product 122 (Scheme 29). 50 Dipp NacNacAl(I) (1) reacted with diphenyl disulfide to afford the symmetrically substituted bis( phenyl sulfide) aluminum complex 123 via the cleavage of the S-S bond in diphenyl disulfide. In a similar fashion, the reaction of 1 with bulky tetraphenyl diphosphine resulted in the cleavage of the P-P bond over the course of 3 d at 70°C to produce the novel aluminum bis(diphenyl phosphido) complex (124) 54 The oxidation of Dipp NacNacGa(I) (2) by using pyridine oxide led to the C-H bond activation of pyridine oxide, yielding Dipp NacNacGa(OH) (η 1 (C),κ 1 (O)-o-C 5 H 4 N-O) (142), and pyridine.…”