Activation of a sp C-H at the methyl substituent was calculated to occur by reductive deprotonation mechanism, analogous to that previously reported for 1 (Figure ). The transition state for breaking the sp C-H bond (TS-1a) was found to be lower in energy (G ‡ = 13.7 vs. 20.8 kcal mol -1 ) than for the competing activation of the sp 2 C-H bond in the 6-position (TS-1b). This finding is consistent with the role of the Fe site as a base in the mechanism and the known pKas of the sp 3 and sp 2 sites. The product of deprotonation, INT-2a is dearomatized and more stable than INT-2b, the corresponding intermediate from sp C-H activation (G°298K = -4.2 vs. 16.1 kcal mol -1 ). Based on our current understanding, it is likely that the proposed mechanistic network is accessible for the entire series of substrates, but that differing substitution patterns on pyridine influence the barrier heights and relative thermodynamic stability of the products. For example, for 4-methypyridine the conversion of the Al-C product to the C-C product 2 → 3 is calculated to be exergonic by G°298K = -7.1 kcal mol -1 , the analogous reaction for 2-methylpyridine described above 8 → 7 is endergonic G°298K = + 4.9 kcal mol -1 . The difference in thermochemistry is likely a consequence of the stability of the chelate (5 vs 6 membered ring) formed in the C-C bond product, alongside the steric congestion of the Al-C product that occurs when the pyridyl group contains methyl substituents adjacent to the metal. Consistent with this latter argument, in no case are Al-C bonded products observed with an ortho-methyl substituent on pyridyl ring. Rather it appears this substitution pattern may destabilise the Al-C bonded product and favour the N-to C-rearrangement and C-C bond formation.