Adducts of organogallium chlorides with hydrazines and the formation of dimeric dialkylgallium hydrazides possessing different ring sizes

The dialkylgallium chlorides R2GaCl (R = Me, Et, CMe3) reacted with hydrazines H2N–N(H)R′ (R′ = CMe3, C6H5) to form the adducts R2ClGa ← NH2–N(H)R′ (1–4), in which the gallium atoms are coordinated by the NH2 nitrogen atoms of the hydrazine ligands. Treatment of these adducts with tert-butyllithium as a base afforded dialkylgallium hydrazides (R2Ga–N2H2R′)2 [5 (R = R′ = CMe3) and 6 (R = CMe3, R′ = C6H5)] by deprotonation of the hydrazine ligands and precipitation of LiCl in two cases only. The remaining adducts gave a substitution reaction at gallium or an unclear reaction course. The hydrazides 5 and 6 adopt different structures in the solid state. The tri(tert-butyl) compound 5 possesses a four-membered Ga2N2 heterocycle in its molecular core with two exocyclic N–N bonds, which represents the structural motif usually observed for dialkylgallium hydrazides. 6 has a five-membered Ga2N3 heterocycle with one endocyclic and one exocyclic N–N bond. That structure is preserved in solution as clearly shown by NMR spectroscopy. The behaviour of 5 in solution is more complicated, which may be caused by cis/trans isomerization.