Hydrogenation and dehydrogenation of chlorotris-(triphenylphosphine)rhodium(I)☆

Abstract A comparison has been made between the amount of hydrogen absorbed per mole of chlorotris(triphenylphosphine)rhodium(I) and the amount of hydrogen quantitatively recoverable by an inert gas purging technique. A discrepancy between these two types of measurements has been found in benzene, methylene chloride and 50% chloroform-ethanol solutions. In the latter mixed solvent the reversibly bound hydrogen:rhodium ratio is only about 0.3 at 298 K, due to the formation of hydridodichlorobis(triphenylphosphine)rhodium (III). This ratio was found to be 0.85 in benzene and 0.66 in methylene chloride at 298 K. These values differ from those determined spectroscopically by other investigators who have studied the hydrogenation equilibria of this important homogeneous catalyst.