Reaction of [(^tBu)Ga(μ₃-Te)]₄ with elemental sulfur and selenium: A facile chalcogenide exchange reaction

A facile chalcogenide exchange is observed for the reaction between [(^tBu)Ga(μ₃-Te)]₄ and elemental sulfur or selenium, resulting in the stoichiometric formation of the appropriate cubane, [(^tBu)Ga(μ₃-E)]₄ (E = S, Se), and metallic tellurium. Each of the intermediate cubane compounds, [(^tBu)₄Ga₄(μ₃-E) _x(μ₃-Te)_4-x (x = 0-4; E = S, Se) have been characterized by NMR spectroscopy and mass spectrometry. The rate of the chalcogenide exchange is dependent not only on the chalcogen (S faster than Se) but also the allotropic form of the chalcogen (catenasulfur, S_∞, faster than S₈). The chalcogen exchange reaction is first order with respect to the cubane, and the ΔH^‡ and ΔS^‡ values have been determined for the reactions with S₈ (64.6 kJ mol^-1, 78.7 J K^-1 mol^-1), catenasulfur (33.3 kJ mol^-1, 84.4 J K^-1 mol^-1), and metallic selenium (73.5 kJ mol^-1, 108 J K^-1 mol^-1). The lack of reactivity of [(^tBu)Ga(μ₃-Se)]₄ with sulfur is proposed to be related to the strength of the cubane Ga-E bond rather than the relative electrochemical reduction potentials of the chalcogens. The reactions of [(^tBu)Ga(μ₃-Te)]₄ with catenasulfur and selenium are inhibited by the deposition of metallic tellurium on the reactant particles, as confirmed by microprobe analysis. The exchange reaction is proposed to be heterogeneous in nature and involve the opening of the cubane core.