The isocyanide ligands in 2b-d were found to be more reactive than the carbonyl in 2a, reacting with the exposed Al-H hydride by an apparent intramolecular pathway. Storage of samples of 2b at room temperature over several hours resulted in its complete consumption and the formation of 5b in >95 % NMR yield. The 1 H NMR spectrum of 5b features a characteristic quartet resonance at δH = 11.47 ppm, as well as the lack of the terminal Al-H signal. X-ray crystallography reveals the migration of the Al-H nucleus onto the isocyanide carbon, with the N now bound to the Al centre (Figure ). A similar pathway was identified for 2d. When 2.2 equiv. of CNXyl is added to 1 the reaction yields 5d' after 7 days at room temperature (>95 % NMR yield), which features a similar Fe-CH resonance to 4b at δH = 10.62 ppm. X-ray crystallography reveals that one of the PMe3 ligands had been replaced by a second equivalent of CNXyl in 5d'. Following this reaction by NMR spectroscopy reveals transient intermediates 2d' and 5d, resulting from ligand exchange and nucleophilic attack by the hydride, respectively. It appears that the thermodynamic driving force for this reaction is sufficiently large that in the absence of exogenous XylNC, samples of 2d gave a mixture of 5d', 1, and PMe3 over the course of several days. DFT calculations suggest that in lieu of an external electrophile, the terminal Al-H of 2b or 2d is able to afford nucleophilic attack onto the adjacent isocyanide ligand (ΔG ‡ = 22.6 kcal mol -1 , ΔG° = -3.3 kcal mol -1 , see Figure ). This is in stark contrast with attack onto the carbonyl in 2a which is both kinetically and thermodynamically inaccessible at room temperature (ΔG ‡ = 32.5 kcal mol -1 , ΔG° = +14.1. kcal mol -1 , see Figure ).