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|Title:||First example of mu(3)-sulfido bridged mixed-valent triruthenium complex triangle (Ru2RuII)-Ru-III(O,O-acetylacetonate)(3)(mu-O,O,gamma-C-acetylacetonate)(3)(mu(3)-S) (1) incorporating simultaneous O,O- and gamma-C-bonded bridging acetylacetonate units. Synthesis, crystal structure, and spectral and redox properties|
|Keywords:||Selective Aromatic Thiolation|
|Publisher:||AMER CHEMICAL SOC|
|Citation:||INORGANIC CHEMISTRY, 42(4), 1322-1327|
|Abstract:||The reaction of mononuclear ruthenium precursor [Ru-II(acac)(2)(CH3CN)(2)] (acac = acetylacetonate) with the thiouracil ligand (2-thiouracil, H2L1 or 6-methyl -2-thiouracil, H2L2) in the presence of NEt3 as base in ethanol solvent afforded a trinuclear triangular complex Ru-3(O,O-acetylacetonate)(3)(mu- O,O,gamma- C-acetylaceto n ate) 3(u FS U If ido) (1). In 1, each ruthenium center is linked to one usual 0,0-bonded terminal acetylacetonate molecule whereas the other three acetylacetonate units act as bridging functions: each bridges two adjacent ruthenium ions through the terminal O,O-donor centers at one end and via the gamma-carbon center at the other end. Moreover, there is a mu(3)-Sulfido bridging in the center of the complex unit, which essentially resulted via the selective cleavage of the carbon-sulfur bond of the thiouracil ligand. In diamagnetic complex 1, the ruthenium ions are in mixed valent (RuRuRuII)-Ru-III-Ru-III state, where the paramagnetic ruthenium(III) ions are antiferromagnetically coupled. The single crystal X-ray structure of 1 showed two crystallographically independent C-3-symmetric molecules, Ru-3(O,O-acetylacetonate)(3)(mu-O,O,gamma-Cacetylacetonate)(3)(mu(3)-S) (1), in the asymmetric unit. Bond distances of both crystallographically independent molecules are almost identical, but there are some significant differences in bond angles (up to 60) and interplanar angles (up to 80). Each ruthenium atom exhibits a distorted octahedral environment formed by four oxygen atoms, two from each of the terminal and bridging acetylacetonate units, one gamma-carbon of an adjacent acetylacetonate ligand, and the sulfur atom in the center of the complex. In agreement with the expected Vold symmetry of the complex molecule, the H-1 and C-13 NIVIR spectra of 1 in CDCl3 displayed signals corresponding to two types of ligand units. In dichloromethane solvent, 1 exhibited three metal center based successive quasireversible redox processes, (RuRuRuIII)-Ru-III-Ru-III-(RuRuRuII)-Ru-III-Ru-II (couple I, 0.43 V vs SCE); (RuRuRuIV)-Ru-III-Ru-III-(RuRuRuIII)-Ru-III-Ru-III (couple II, 1.12 V); and (RuRuRuIII)-Ru-III-Ru-III-(RuRuRuII)-Ru-III-Ru-III (couple III, -1.21 V). However, in acetonitrile solvent, in addition to the three described couples [(couple 1), 0.34 V; (couple II), 1.0 V; (couple III), -1.0], one irreversible oxidative response ((RuRuRuIV)-Ru-III-Ru-III --> Ru-III- (RuRuIV)-Ru-IV or oxidation of the coordinated sulfide center) appeared at E-pa 1.50 V. The large differences in potentials between the successive couples are indicative of strong coupling between the ruthenium ions in the mixed-valent states. Compound 1 exhibited a moderately strong charge-transfer (CT) transition at 654 nm and multiple ligand based intense transitions in the UV region. In the (RuRuRuIII)-Ru-III-Ru-III (1(+)) state, the CT band was slightly blue shifted to 644 nm; however, the CT band was further blue shifted to 520 nm on two-electron oxidation to the (RuRuRuIV)-Ru-III-Ru-III (1(2+)) state with a reduction in intensity.|
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