The purpose of this work was to explore the possibility of using iron(II) hydrides in CO2 reduction and to compare their reactivity to that of their ruthenium analogues. Fe(bpy)(P(OEt)(3))(3)H+ and Ru(bpy)(P(OEt)(3))(3)H+ do not react with CO2 in acetonitrile, but the one-electron-reduction products of Ru(bpy)(P(OEt3)(3)H+ and Ru(bpy)(2)(P(OEt3)H+ and the two-electron-reduction product of Fe(bPY)(P(OEt3)(3)H+ do. Ru(bpy)(2)(P(OEt)(3))H+ also reacts slowly with CO2 to give a formate complex [as reported previously by Albertin et al. (Inorg. Chem. 2004, 43, 1336)] with a second-order rate constant of similar to 4 x 10(-3) M-1 s(-1) in methanol. The structures for the hydride complexes [Fe(bpy)(P(OEt3)(3)H](+) and [Ru(bpy)(2)(P(OEt)(3))H](+) and for the (eta(5)-Cp)bis- and -tris-PTA complexes (PTA = 1,3,5-triaza-7-phosphatricyclo-[3.3.1.1.3.7]decane) of iron(II) are reported. These and the CpFe(CO)(bpy)(+) and (FePNNP)-P-II compounds have been subjected to electrochemical and UV-vis spectroscopic characterization Fe(bpy)(P(OEt3)(3)H+ exhibits a quasi-reversible oxidation at +0.42 V vs AgCl/Ag in acetonitrile, Ru(bpy)(P(OEt3)(3)H+ and Ru(bpy)(2)(P(OEt3)H+ are oxidized irreversibly at +0.90 and +0.55 V, respectively, vs AgCl/Ag. The reduction site for Fe(bpy)(P(OEt)(3))(3)H+ and Fe(bpy)(P(OEt3)(3)(CH3CN)(2+) appears to be the metal and gives rise to a two-electron process. The bpy-centered reductions are negatively shifted in the ruthenium(II) hydride complexes, compared to the acetonitrile complexes. The results of attempts to prepare other iron(II) hydrides are summarized.