The quantitative hydrogenation of cis-1,4-poly(isoprene) (CPIP) provides an easy entry to the alternating copolymer of ethylene-propylene, which is difficult to prepare by conventional polymerization. The homogeneous hydrogenation of CPIP, in the presence of OsHCl(CO)(O-2)(PCy3)(2) as catalyst, has been studied by monitoring the amount of hydrogen consumed during the reaction. The final degree of olefin conversion measured by computer-controlled gas uptake apparatus was confirmed by infrared spectroscopy and H-1 nuclear magnetic resonance analysis. Kinetic experiments for CPIP hydrogenation in toluene solvent indicate that the hydrogenation rate is first order with respect to catalyst and carbon-carbon double bond concentration. A second-order dependence on hydrogen concentration for low values and a zero-order dependence for higher values of the hydrogen concentration was observed. The apparent activation energy for the hydrogenation of CPIP over the temperature range of 115-140degreesC was 109.3 kJ/mole. Mechanistic aspects of this catalytic process are discussed. (C) 2003 Wiley Periodicals, Inc.