Differing Reactivities of Cp*Ga toward Diazabutadienes:  Synthesis of Novel 1-Galla-2,5-diazoles and of the Known Radical Ga[But-DAB]₂

The heterocycles ( 1 ) and ( 2 ) were obtained by oxidative addition of (η 5 -pentamethylcyclopentadienyl)gallium(I) (Cp*Ga) to Dipp-DAB (1,4 - bis(2,6-diisopropylphenyl)-1,4-diazabuta-1,3-diene) and Dep-DAB (1,4 - bis(2,6-diethylphenyl)-1,4-diazabuta-1,3-diene), respectively. Compounds 1 and 2 are the first examples of monomeric gallium-containing heterocycles of the diazabutadiene (DAB) type. 1 was structurally characterized by X-ray crystallography. In contrast, the reaction of Cp*Ga with Bu t -DAB (1,4-di- tert -butyl-1,4-diazabuta-1,3-diene) led to the formation of the known radical (Ga[Bu t -DAB] 2 ) ( 3 ) in high yield, thus providing an alternative synthesis to the cocondensation technique used previously. Radical 3 was further characterized by 1 H NMR spectroscopy and cyclic voltammetric studies, which revealed two reversible oxidation steps and one reversible reduction step.