In the past decade, considerable progress has been made in the understanding of catalytic systems which simultaneously possess both mononuclear and dinuclear intermediates. The present contribution begins by reviewing the necessary background concerning stoichiometric binuclear elimination. This is followed by a summary of in situ FTIR studies on corresponding homometallic and hetero-bimetallic catalytic binuclear eliminations. Pure component spectral estimates of the constituents present during the catalysis as well as their associated concentration profiles are used in order to model the rates of binuclear elimination during alkene hydroformations. The rates of product formation are linear-quadratic in metal loading for the homometallic case and linear-bilinear in the hetero-bimetallic case. Hetero-bimetallic catalytic binuclear elimination provides a well-defined mechanistic basis for synergism. (C) 2009 Elsevier B.V. All rights reserved.