Unusual condensation of ethylene glycol with coordinated 1,10-phenanthroline-5,6-dione in [Ru(phen-dione)2Cl2] and its cyclometallated complex, [Ru(phpy-κ2N,C2′)(phen-diox)2](PF6)

Abstract

A novel cyclometallated Ru(II) derivative of 1,10-phenanthroline-5,6-dione (phen-dione), [Ru(phpy-κ2N,C2′)(phen-diox)2](PF6), where phpy-κ2N,C2′ is 2-phenylpyridine and phen-diox is 2,3-dihydro-4a,12b-(epoxyethanooxy)[1,4]dioxino[2,3-f][1,10]phenanthroline, has been prepared by the metal-assisted effect of [Ru(phen-dione)2Cl2] via an unusual condensation of the coordinated phen-dione ligand with ethylene glycol which led to the formation of [Ru(phen-diox)2Cl2]. The condensation reaction could not proceed in the absence of [Ru(phen-dione)2Cl2]. DFT calculations showed that the energy of the LUMO of [Ru(phen-dione)2Cl2] is about 12.430kcal/mol lower than that of the uncoordinated phen-dione ligand. The cyclometallated complex has been characterized by elemental analysis, spectroscopic and spectroelectrochemical (SEC) techniques, cyclic voltammetry and X-ray crystallography. X-ray analysis of the complex shows an elongation of one of the five Ru–N bonds due to a strong trans effect of the carbanionic ligand. The electrochemical data of the complex demonstrate a strong σ-donating character of the anionic phenylpyridine ligand. UV–vis spectroelectrochemical studies of the complex in acetonitrile show a reversible redox behavior, evaluated by the maintenance of isosbestic points in the UV–vis spectrum for both forward oxidation and reverse reduction processes. The complex is very weakly emissive at room temperature in degassed acetonitrile with λem=546nm and ϕem=0.02%.