Synthesis and characterization of water-soluble arene-ruthenium complexes and their application in biphasic olefin oxidation

<p>New water-soluble complexes [(η<sup>6</sup>-C<sub>6</sub>H<sub>6</sub>)RuCl(C<sub>5</sub>H<sub>4</sub>N-2-CH = N-R)]Cl (<b>1</b>) (with R = 4-hydroxymethylphenyl (<b>a</b>), 2,4-dichlorophenyl (<b>b</b>), 2-fluorophenyl (<b>c</b>), 3-carboxyphenyl (<b>d</b>)) have been synthesized by reacting [(η<sup>6</sup>-C<sub>6</sub>H<sub>6</sub>)Ru(μ-Cl)Cl]<sub>2</sub> with the <i>N</i>,<i>N</i>′-bidentate ligands in a 1:2 ratio. Full characterization of all complexes was accomplished using <sup>1</sup>H and <sup>13</sup>C NMR, elemental analyses, UV-Vis spectroscopy, IR spectroscopy and single crystal X-ray crystallography for determination of the structure of <b>1d</b>, as <b>1d</b>·4H<sub>2</sub>O. The single crystal structure confirmed coordination of the ligand to the ruthenium(II) center leading to a structure commonly described as a pseudo-octahedral, three-legged piano stool. The geometry around the Ru(II) center is such that the arene ring occupies the apex of the stool while the <i>N</i>,<i>N</i>′-bidentate ligand and a chloride occupy the base of the stool. The synthesized Ru(II) complexes were tested as catalysts for oxidation of styrene using NaIO<sub>4</sub> as a co-oxidant in a biphasic system. All complexes were active, giving good yields of benzaldehyde. Catalyst <b>1c</b> was later investigated for olefin oxidation and gave high yields of the corresponding aldehydes as the major products in all cases.</p> <p></p>