ORGANOMETALLIC PHOTOCHEMISTRY IN AQUEOUS-SOLUTION - SYNTHESIS, CRYSTAL AND MOLECULAR-STRUCTURE, AND PHOTOCHEMISTRY OF THE (ETA-5-C5H4COOH)2W2(CO)6 COMPLEX - GENERATION OF 19-ELECTRON ORGANOMETALLIC COMPLEXES IN AQUEOUS-SOLUTION AND THEIR USE AS REDUCING AGENTS - PHOTOCHEMICAL PRODUCTION OF HYDROGEN

The synthesis, crystal structure, and photochemistry of the (CpCOOH)2W2(CO)6 (CpCOOH = eta-5-C5H4COOH) complex are described. The pK(a) of the molecule is 4.5, and it is soluble in aqueous solutions at pH 6 or higher. The photochemistry of the molecule is similar to the photochemistry of the Cp2W2(CO)6 (Cp = eta-5-C5H5) complex: irradiation into the low-energy tail of the lowest energy absorption band (lambda-max = 488 nm; d-pi --> sigma*) results in homolytic cleavage of the W-W bond to form (CpCOOH)W(CO)3 radicals in nonaqueous solvents or (CpCOO-)W(CO)3 radicals in aqueous solution. These 17-electron radicals can be trapped with chlorine atom donors (e.g., CCl4 in nonaqueous solution or CCl3COO- in aqueous solution), or they can react with a ligand (e.g., PPh2R-; R- = C6H4SO3-) to form a reactive 19-electron adduct. Like their counterparts in nonaqueous solvents, the 19-electron adducts generated in aqueous solution are good reductants. They were used to reduce a variety of water-soluble substrates, including Fe(CN)6(3-), methyl viologen, and cytochrome c. Hydrogen is also formed when the dimer is irradiated in aqueous solution in the presence of a ligand. Crystals of the complex (C5H4COOH)2W2(CO)6.2C4H8O (C26H26O12W2) are triclinic, space group P1BAR, with a = 7.502 (2) angstrom, b = 10.493 (5) angstrom, c = 10.670 (6) angstrom, alpha = 118.98 (3)-degrees, beta = 100.25 (3)-degrees, gamma = 94.35 (3)-degrees, V = 710.2 (6) angstrom 3, and Z = 1. The complex crystallizes in an anti conformation, with a "trans-like" orientation of the two COOH groups with respect to each other. The W-W bond length of 3.215 (3) angstrom is nominally shorter than that in (eta-5-C5H5)2W2(CO)6 (3.222 (1) angstrom).