Reactions of an Anionic Gallylene with Azobenzene or Azide Compounds Through C(sp²)–H and C(sp³)–H Activation

Abstract

The activation of inert C–H bonds remains a challenge in current chemistry. Here, we report the excellent reactivity of the anionic gallylene species [LGa:][Na(THF)3] (L = [(2,6-iPr2C6H3)NC(CH3)]22−, 1) that allows the selective activation one ortho sp2 C–H bond of several azobenzene and azide derivatives at ambient temperature, with the transfer of the hydrogen atom to one of the nitrogen atoms. The process leads to the formation of the aryl amido products [LGa-κ2N,C-PhNN(H)(p-R-C6H3)][Na(solvent)3] (2, R = H solvent = DME (1,2-Dimethoxyethane); 3, R = –OMe, solvent = DME; 4, R = –NMe2 solvent = THF), [LGa-κ2N,C-(m-CH3-C6H4)NN(H)(m-CH3-C6H3)][Na(15-C-5)2] (5) with new Ga–C and Ga–N bonds. Moreover, 1 is also effective for the C–H activation of two azides RN3 (R = 2,4,6-Me3C6H2 or 2,6-iPr2C6H3), resulting in the formation of gallium amides [LGa(NH-2-(CH2)-4,6-Me2C6H2)][Na(15-C-5)2] (6) and [LGa(NH-2,6-iPr2C6H3)2][Na(THF)5] (7) through intra- or intermolecular sp3 C–H amination. Significantly, these reactions occur for the highly challenging activation of inert C(sp2)–H and C(sp3)–H bonds, thus demonstrating the excellent reactivity of the Ga(I) species 1. The products 2–7 were characterized by X-ray crystallography, 1H and 13C NMR, UV–vis spectroscopy, and density functional theory (DFT) calculations.

Keywords

• C–H activation
• gallylene
• azobenzene
• organic azides
• α-diimine ligands