The mechanistic sequence from 1 → 2a → 3 was considered in more detail (Figure ). sulfur-containing molecules. The observation of two sequential C-S bond activation events in the reaction of 1 with thiophene is unique. The result prompted us to re-investigate the addition of 1 to furan, in no case, however, were double C-O activation products observed. While this divergent reactivity is yet to be fully understood, it remains likely that the second insertion transition state TS-3, which brings together two bulky aluminium fragments, is susceptible to steric effects that may be more pronounced in furan derivatives which possess shortened C-X and Al-X bonds compared to the sulfur analogues (X = O, S).