Synthesis, electrochemistry, and reactivities of trans-[RuVI(L)O2]2+(L =N,N′-dimethyl-N,N′-bis(2-pyridylmethyl)propylenediamine

Abstract

The synthesis and characterization of the ligand N,N′-dimethyl-N,N′-bis(2-pyridylmethyl)-propylenediamine (L) and the complex trans-[Ru^VI(L)O₂]²⁺ are described. The complex has been characterized by u.v.–visible [d_xy→d_π*(d_π*=d_xz,d_yz) at 380–420 nm] and i.r. [ν_asym(RuO₂) at 860 cm^–1] spectroscopy. At pH 1.0 it exhibits three reversible couples Ru^VI–Ru^IV, Ru^IV–Ru^III, and Ru^III–Ru^II at potentials of 0.89, 0.60, and 0.28 V respectively vs. saturated calomel electrode. The Ru^VI–Ru^IV couple splits into two reversible one-electron couples Ru^VI–Ru^V and Ru^V–Ru^IV in alkaline solutions (pH > 9). The complex is a powerful oxidant, capable of oxidizing toluene to benzaldehyde, alcohols to aldehydes/ketones, tetrahydrofuran to γ-butyrolactone, and norbornene to exo-2,3-epoxy-norbornane in high yields at room temperature. Oxidation of cis- and trans-stilbenes gave benzaldehyde and trans-stilbene oxides.