Charge-transfer complexes in homogeneous catalysis

It is shown that these complexes can be formed between the reactants in redox reactions. Oxidizing and reducing agents are classified on the basis of charge-transfer capacity, which is defined by the integral for the overlap between the filled orbital of the reductant and the free one of the oxidant. Unfilled diffuse d-orbitals most readily give such complexes. Homogeneous catalysis of a redox reaction involves charge transfer in either direction between the catalyst (which has partly filled d-orbitals) and one of the reagents. The transfer is very much dependent on the orientation, so activators play a large part.