SYNTHESIS AND PHOTOCHEMISTRY OF THE AQUEOUS-SOLUBLE (MU-5-C5H4CH2CH2NH3+)2MO2(CO)6 COMPLEX - GENERATION OF 19-ELECTRON COMPLEXES IN AQUEOUS-SOLUTION

The synthesis and photochemistry of the (e-C5H4CH2CH2NH3+)2Mo2(CO)6 complex are described. The N03 salt is soluble in aqueous solutions at pH 8 or lower; the PF6- salt was used in organic solvents. The photochemistry of the molecule is similar to the photochemistry of the Cp2Mo2(CO)6 (Cp = eta5-C5H5) complex: irradiation into the low-energy tail of the lowest energy absorption band (lambda(max) almost-equal-to 503 nm; dpi --> sigma*) results in homolytic cleavage of the Mo-Mo bond to form (eta5-C5H4CH2CH2NH3+)Mo(CO)3 radicals. These 17-electron radicals can be trapped with chlorine atom donors (e.g., CCl4 in nonaqueous solution or CCl3CH2OH in aqueous solution) to form (eta5-C5H4CH2CH2NH3+)Mo(CO)3Cl. Irradiation of (eta5-C5H4CH2CH2NH3+)2Mo2(CO)6 in the presence of ligands [e.g., phosphines in nonaqueous solution or water-soluble phosphines such as PTA (phosphatriazaadamantane) in aqueous solution] resulted in disproportionation of the dimer complex. The disproportionation reactivity is consistent with the intermediate formation of 19-electron adducts. Like their counterparts in nonaqueous solvents, the putative 19-electron adducts generated in aqueous solution are good reductants. They were used to reduce methylviologen and cytochrome c in aqueous solution. Reduction of protons to H-2 did not occur, and this led us to reexamine our earlier results in which we suggested that 19-electron complexes formed by irradiation of (CpCOOH)2W2(CO)6 in basic aqueous solution reduced water to H-2. CO2 is formed in a 1:1 ratio with H-2 in this reaction, and we propose the water-gas shift reaction is the source of the H-2.