Paramagnetic organometallics formed by o-metallation of phenolic Schiff bases by ruthenium(III)

Abstract

The reaction of Ru(PPh₃)₃X₂ (X= Cl, Br) with the Schiff base condensate of 4-substituted benzaldehyde (RC₆H₄CHO) and 2-aminophenol under aerobic conditions affords the complexes Ru^III(RL)(PPH₃)₂X in which RL is the Schiff base ligand bound to the metal centre at the phenolic oxygen (deprotonated azomethine nitrogen and an ortho carbon atom (deprotonated) of the benzaldehyde fragment. The complexes behave as one-electron paramagnets; and give rhombic EPR spectra, that have been analysed to furnish values of axial and rhombic distortion parameters as well as the energies of the two expected ligand field transitions within the t₂ shell. One of the transitions has been experimentally observed in the predicted region. The complexes are electroactive and display ruthenium(III)- ruthenium(II) (E_½ -0.5 to -0.8 V vs. SCE) and ruthenium(IV)-ruthenium(III) (E_½ 0.4 to 0.8 V) couples. The E _½ values vary linearly with the Hammett constant of the substituent R. The role of phenolato-coordination in stabilizing the trivalent state of ruthenium is noted.