The kinetics and mechanisms of the reactions of photochemi- cally generated tris(bipyridyl)ruthenium(1+) ion with various metal complexes were studied. The rates of reduction of some Co(III) complexes (for example Co(en)(,3)('3+), Co(NH(,3))(,6)('3+), and MeCo(dmgH)(,2)) were at, or near, the diffusion controlled limit. Several rare earth ions, Eu('3+), Yb('3+), and Sm('3+) were also reacted with the ruthenium(1+) complex. Yb('3+) was reduced; however, the reaction was just above the limits of detection. Sm('3+) was not reduced, in accord with the thermodynamics of the reaction;The reductions of some Cr(III) complexes, including pentaaquo- (organo)chromium(2+) ions and pentaaquo(pyridine)chromium(3+) ions, were also studied. The reduction of the organochromium(2+) complexes proceeded at a rate that was similar to the Cr(H(,2)O)(,6)('3+) ion. The possible existence of a long-lived organochromium(1+) species is discussed. The reduction of the pyridinechromium(3+) complexes proceeds by direct electron transfer to the chromium center; the pyridine does not exist, during the electron transfer, as a bound pyridyl radical. This view is supported by a comparison between the reaction constants, (rho), for the reduction of substituted pyridines and the reduction of metal complexes containing ligated pyridines. A rate constant for the reaction between benzylradical and Eu('2+) is also estimated;The homogeneous catalytic production of H(,2) from reduced metal halide solutions (M('2+) = Cr('2+), Eu('2+), V('2+)) is presented. The catalyst is a cobalt(II) macrocyclic complex, Co(dmgBF(,2))(,2), which is reduced by the M('2+) ions to form, ultimately, a hydridometal complex. This complex leads to the evolution of H(,2) in the acidic solutions employed. The mechanism of the reaction is discussed in terms of the Michaelis-Menten scheme for enzyme catalysis;A photochemical method for the generation of 1-hydroxy-1-methylethyl radical for kinetic study is presented. This radical is reacted with BrCo(dmgH)(,2) and ClCo(dmgH)(,2) to produce the highly;colored Co(dmgH)(,2) complex, which serves as the indicator for the reaction; ('1)DOE Report IS-T-1175. This work was performed under contract W-7405-Eng-82 with the Department of Energy.