Reactions of relatively simple coordination complexes have been examined as tests of PCET.
*The comproportionation of a Ru(II) aquo and a Ru(IV) oxo (bipy = (2,2'-bipyridine, py = pyridine): 
:[(bipy)(py)Ru(O)] + [(bipy)(py)Ru(OH)] → 2 [(bipy)(py)Ru(OH)]
*Electrochemical reactions where reduction is coupled to protonation or where oxidation is coupled to deprotonation.