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

Abstract

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.