The photochemistry and electronic spectra of [lV^f^-CsHshfCO),*] (M = Fe, Ru) are reported. Each complex undergoes efficient M-M bond cleavage subsequent to electronic excitation in CCU solution to yield [IVfl^-CsHsHCO^Cl] as the only M-containing product. The disappearance quantum yields at 366 nm for = Fe and Ru are 0.23 and 0.44, respectively, in CCI4 where the Fe species is fully in the bridged form and the Ru species is a mixture of the bridged and nonbridged form. The quantum yield for disappearance of the Ru species is the same in CH3CN and hydrocarbon solution of 0.1 M CCI4 where the structure in solution is essentially fully bridged (CH3CN) or ~50/50 bridged/nonbridged (hydrocarbon). The results support the conclusion that carbonyl bridged metal-metal bonds can be efficiently cleaved by optical excitation. The quantum yields for both M = Fe and Ru are somewhat wavelength dependent, with higher energy excitation giving modestly increased quantum yields. The electronic spectrum of the Ru species is very solvent and temperature sensitive in accord with known effects on the equilibrium between the bridged and nonbridged form. The • -+ * absorption in the bridged form is at

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