In consideration that assigning rank can be highly subjective, we have opted for a qualitative approach to categorizing the proposed substrate union's likelihood of success. In green, there is plenty of precedent of that substructure being achievable in good yield (>50% yield) barring the competition of other functional groups. In yellow, there are fewer reports of that substructure present or the general yield in accessing that substructure is moderate (20% to 50% yield). In red, the target substructure is a current limitation or stretch of the method (<20% yield). Finally, grey represents cases where there is no report of such a cross-coupling being achieved either photo-or electrochemically. If anything, the red and grey indications are meant to highlight exciting areas for future research efforts. Notably absent, and outside the scope of these accounts, is the plethora of contemporary methodologies that forge similar bonds using organic or metallic reductants and oxidants. Rather than describe every possible pairing, key observations from this guide and their implications on the frontiers of first-row transition metal catalysis will be highlighted.