Diosmacyclobutanes Os2(CO)8(olefin) undergo facile exchangereactions with olefins and acetylenes. An associative mechanism is excluded by the observation of saturation kinetics as the concentration of the entering olefin (butyl acrylate) is increased. Multivariate analysis of the rate as a function of [C2H4] (determined from solubility measurements in decane/butyl acrylate mixtures) and [butyl acrylate]