An additional experiment supports the claim that MeCN is a suitable solvent owing to more than just its solvation properties: when 5 vol% of MeCN is added to toluene, 57% of SA with 92% selectivity is obtained, a yield which is significantly higher than the one obtained in toluene alone in similar conditions (4%, Table To conclude, the trends observed are consistent with the mechanistic model proposed in Scheme 3, where the Lewis base may either be the solvent or the substrate, and where the disproportionation of the [Co2(CO)8] is a key step for the generation of an active species: no carbonylation activity is observed in the conditions where the disproportionation of the precursor [Co2(CO)8] is less favoured, i.e., in a noncoordinating solvent, and at high CO pressure (see Table , entries 3 and 6).