The cobalt center in H Co(CO)(4) exchanges with those in Co-2(CO)(8) through a facile hydride ligand transfer reaction which has been studied by Co-59 NMR line-shape analysis over the temperature range of 80 to 200 degrees C and total system pressures up to 370 atm in supercritical carbon dioxide. The lifetime of the cobalt center in HCo(CO)(4) varies from 2 ms at 80 degrees C to 10 mu s at 200 degrees C, exhibiting an activation energy of 15.3 +/- 0.4 kcal/mol. The hydride ligand transfer process is highly specific for the HCo(CO)(4) and Co-2(CO)(8) complexe(s). Thus, neither Co-4(CO)(12) nor MnCo(CO)(9) exhibit measurable chemical exchange line broadening in the Co-59 NMR spectra within solutions where the resonances for HCo(CO)(4) and Co-2(CO)(8) coalesce.