Reactions of Low-Valent Gallium Species with Organic Azides: Formation of Imido-, Azoimido-, and Tetrazene Complexes

The reactivity of two α-diimine-ligated digallanes, [L^2-Ga-GaL^2-] (L^a = [(2,6-iPr₂C₆H₃)NC(CH₃)]₂, dpp-dad, 1; L^b = 1,2-[(2,6-iPr₂C₆H₃)NC]₂C₁₀H₆, dpp-bian, 2), and a gallylene, [(L^a)^2-GaNa(THF)₃] (3), toward organic azides was studied. Reaction of digallane 1 or 2 with trimethylsilyl azide (Me₃SiN₃), 2-azido-benzonitrile (2-CNC₆H₄N₃), or tosylazide (TosN₃) results in imido-bridged complexes, [(L^a)^·-Ga(μ-NSiMe₃)₂Ga(L^a)^·-] (4) [(L^b)^·-Ga(μ-NSiMe₃)₂Ga(L^b)^·-] (5), [(L^b)^·-Ga(μ-2-CNC₆H₄N)₂Ga(L^b)^·-] (6), and [(L^b)^·-Ga(μ-NTos)₂Ga(L^b)^·-] (7), with elimination of dinitrogen. Treatment of 1 or 2 with 1-adamantyl azide (1-AdN₃), on the other hand, affords the unsymmetrical dinuclear complexes [(L^a)^·-Ga(NAd)(N₃Ad)Ga(L^a)^·-] (8) and [(L^b)^·-Ga(NAd)(N₃Ad)Ga(L^b)^·-] (9), which contain both imido and triazene bridges. Different from the Ga(II) complexes 1 and 2, the reactions of Ga(I) species 3 with benzylazide or trimethylsilyl azide result in the tetrazene complex {Na(THF)}₂[(L^a)^2-Ga(benzyl-N₄-benzyl)]₂ (10) and amide complex {Na(THF)₄}[(L^a)^2-Ga(NHSiMe₃)(benzyl)] (11). It is likely that these latter transformations proceed via the transient formation of the corresponding Ga═N imide complex, which undergoes either cycloaddition with a second azide (to form 10) or activation of the C-H bond of methyl in one solvent toluene molecule (to yield 11).