Synthesis, structural characterization and catalysis of ruthenium(II) complexes based on 2,5-bis(2′-pyridyl)pyrrole ligand

Treatment of the 2,5-bis(2′-pyridyl)pyrrolato (PDP−) anion with {Ru(COD)Cl2}n in THF readily yielded [Ru(PDP)(COD)Cl] (1) in almost quantitative yield. Anion metathesis of 1 in organic solvent by NO3− and OTf− (OTf− = triflato) gave [Ru(PDP)(COD)(NO3)] (2) and [Ru(PDP)(COD)(OTf)] (3), and in aqueous solution by BF4− and PF6− afforded aqueous complexes [Ru(PDP)(COD)(H2O)](BF4) (4+·BF4−) and [Ru(PDP)(COD)(H2O)](PF6) (4+·PF6−), respectively. Treatment of 1 with PhICl2 in CH2Cl2 afforded 5 with halogenated pyrrole. These complexes exhibit similar structure, including one Ru(II) atom, one 2,5-bis(2′-pyridyl)pyrrole and one monodentate anion or aqua ligand. Each Ru(II) tightly binds to three adjacent coplanar sites of PDP− ligand to form a meridional configuration. Complex 1 with NaIO4 as the oxidant in EtOAc–CH3CN–H2O (ratio = 3 : 1 : 2) proved to be highly effective in the catalytic oxidation of olefins to carbonyl products.