The properties of the base are crucial for an effective process since it fulfils multiple roles: coordination to M and deprotonation of the [M-(heteroaryl-H)] + complex, with the resultant [(Base)H] + then key for protonating the Zn-H/Al-Me containing complex. Initial guidelines for selecting an appropriate base include: (i) sufficiently low nucleophilicity towards M to enable displacement by an incoming heteroarene; (ii) sufficient basicity to deprotonate the resultant [M-(heteroaryl-H)] + complex. Furthermore, combining (i) and (ii) needs to produce a C-H metalation phase that is not too uphill energetically. This is crucial as a significantly endergonic metalation phase will increase the overall energy span of the process once the barrier in the second half of the catalytic cycle, the dehydrocoupling phase, is taken into account, potentially making it too high to proceed. Given that C-H metalation is endergonic, the dehydrocoupling step needs to have a relatively low barrier pathway for the overall cycle to be energetically feasible.