The results show that the condensation of ZnEt2(THF)2 (18A/18B) is moderately energetic (-64 to -28 kJ mol -1 ) and thus quite irreversible, albeit with significant deactivation between the first and the second steps. In contrast, the condensation of ZnCl2(THF)2 (21A/21B) is a clear example of the limits of the CUBE-based synthetic approach as the predicted ΔG 298.15 is positive (+13 to +20 kJ mol -1 ). Therefore, the equilibrium is shifted towards CUBE + ZnCl2 and the condensation is not spontaneous.