Thc role o f metalloenzymes in important biological transformations has attracted incrcasing attention over the past sever-;II decades. Of the many chemical transformations mediated by enzymes, few are a s challenging ;is multielectron redox reactions. Kcccnt studies have revealed ;I partial structiirnl and mechanistic dcscription o f these redox-active metallocn/ymes. but thcrc is much still to be Icarned regarding the mechanisms of substrate transformation. Due to the complexity of the metalloenzyme systems, simplified model systems are employed to mimic structural or functional features of the enzyme. In multielectron redox enzymes, several metals are probably involved in both substrate binding and the subsequent redox reactions. Thus, functional mimics of multielectron redox enzymes might also need two or more metal centers to be efficacious. The roles of multiple metal centers are to 1) increase the substrate's affinity for the catalyst, 2) increase the rate of electron transfer to the bound substrate, 3 ) increase the reactivity of the bound substrate, and 4) inhibit deleterious side reactions. Determining the importance of each factor may help in the development of these catalysts. Cofacial metallodiporphyrins, because of the control they provide over the geometric and electronic properties of the synthetic reaction center, are ideal bimetallic model complexes. The knowledge gained from model studies will help in understanding the mechanisms of metalloenzymes and can be used to design new homogeneous catalysts to effect multielectron transformations.