The kinetics for the bridge-to-chelate isomerization of the dppe ligand in H4Ru4(CO)(10)(dppe) have been investigated by UV-vis and NMR spectroscopies over the temperature range of 308-328 K. The isomerization of the ligand-bridged cluster 1,2-H4Ru4(CO)(10)(dppe) (1-br) was found to be reversible by P-31 NMR spectroscopy, affording a K-eq = 15.7 at 323 K in favor of the chelating dppe isomer 1-ch. The forward (k(1)) and reverse (k(-1)) first-order rate constants for the reaction have been measured in different solvents and in the presence of ligand-trapping agents (CO and PPh3). On the basis of the activation parameters and reaction rates that are unaffected by added CO and PPh3, a sequence involving the nondissociative migration of a phosphine moiety and two CO groups between basal ruthenium centers is proposed and discussed.