The reaction of CpMoMn(mu-S-2)(CO)(5), 1, with 1,4-benzoquinone in the presence of irradiation with visible light yielded the quinonedithiolato complex CpMoMn(CO)(5)(mu-S2C6H2O2), 2. The new complex CpMoMn(CO)(5)(mu-S2C6Cl2O2) (4) was synthesized similarly from 1 and 2,3-dichloro-1,4-benzoquinone. Compounds 2 and 4 were reduced with hydrogen to yield the hydroquinone complexes CpMoMn(CO)(5)[mu-S2C6H2(OH)(2)], 3, and CpMoMn(CO)(5)[mu-S2C6Cl2(OH)(2)], 5. UV-vis irradiation of solutions of Fe-2(CO)(6)(mu-S-2) and 1,4-benzoquinone yielded the hydroquinone complex Fe-2(CO)(6)[mu-S2C6H2(OH)(2)], 6. Compound 6 was oxidized to the quinone complex Fe-2(CO)(6)(mu-S2C6H2O2), 7, by using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone. Substitution of the CO ligands on 6 by PPh3 yielded the derivatives Fe-2(CO)(5)(PPh3)[mu-S2C6H2(OH)(2)], 8, and Fe-2(CO)(4)(PPh3)(2)[mu-S2C6H2(OH)(2)], 9. The electrochemical properties of 3, 5, 6, 8, and 9 were measured by cyclic voltammetry. The molecular structure of each of the new compounds 2-9 was established by single-crystal X-ray diffraction analyses.