Interaction of osmium tetroxide (OsO4) with a series of halide ions (X1 = I1, Br1, Cl1, and F1) is examined. Stable 1:1 adducts, [OsO4(X)]1 (1X), are formed in the case of Br1, Cl1, and F1, whereas redox reaction takes place with I1 to give [OsVIIO4]1 and I•. The adduct formation constant (KfX) increases as the basicity of the halide ion increases (Br1 < Cl1 < F1). Upon the adduct formation, the symmetric (¯(Os=O)sym) and asymmetric (¯(Os=O)asym) Os=O stretching vibration energies are lowered as compared with those of OsO4. The X-ray crystallographic analyses of the halide adducts indicate that the structural distortion of the osmium center from tetrahedron to trigonal bipyramid becomes larger as the KfX value becomes larger. 1F shows much higher reactivity compared with 1Br and 1Cl in the oxidation of benzyl alcohol to benzaldehyde, even though 1F has a lower reduction potential compared to 1Br and 1Cl. Mechanistic details of the alcohol oxidation reaction are evaluated by kinetic studies including Hammett analysis and kinetic deuterium isotope effect as well as by DFT calculations.
!!!All Science Journal Classification (ASJC) codes
- 化学 (全般)