Dihydrogen has been found to react photochemically with bimetallic compounds of the form [(η 5 -C 5 H 5 )M(CO) n ] 2 , where M ) Mo or W, n ) 3, M ) Fe or Ru, n ) 2, to give the corresponding metal hydrides, (η 5 -C 5 H 5 )M(CO) n H. Hydride formation is only significant when the photolysis wavelengths are in the high-energy regions known to trigger CO loss from these compounds, and hydride formation is suppressed by added CO, making it likely that the reaction involves oxidative addition of H 2 to an electron-deficient, CO-loss intermediate.