These calculations, in conjunction with the experimental results presented, suggest that the key benefits of the mechanical bond in 4b are threefold: i) it enhances the basicity of the bipyridine unit, increasing catalyst activity by favouring deprotonation of the substrate; ii) it enforces a stacked orientation for the bipyridinium and NDI units, which increases the polarizability of protonated species, favouring anion-π catalysis and iii) the axle blocks the cavity of the bipyridine ring, preventing the formation of a threaded structure with the substrate, as observed for 1H + .