The arsenic-bridged bimetallic compounds (CO)4FeAs(CH3)2M (M = Mn(CO)4, 1 ; M = Co(CO)3, 2 ; M = Mo(C5H5)(CO)2, 3) were investigated as possible CO and alkene hydrogenation catalysts. Heating these compounds under H2 did not lead to any observable metal dihydride species but gave thermal decomposition. Thermal stabilities were found to be in the order 3 > 1 > 2. 1 and 3 reacted with CO at 45 °C and 110 °C, respectively, to give compounds 5 and 6 in which the metal/3-metal bond has been cleaved and CO added. Heating 1, 2, or 3 under CO and H2 gave no observable CH3OH or CH4. Evidence that metal hydride species might be in equilibrium with 1, 2, or 3 was obtained from the observation that solutions of 1, 2, or 3 which are heated under H2 catalyze the hydrogenation of 1-octene to n-octane and the isomerization of 1-octene to cis- and trans-2-octene.