PARAMAGNETIC ORGANOMETALLICS FORMED BY O-METALATION OF PHENOLIC SCHIFF-BASES BY RUTHENIUM(III)

The reaction of Ru(PPh3)3X2 (X = Cl, Br) with the Schiff base condensa te of 4-substituted benzaldehyde (RC6H4CHO) and 2-aminophenol under ae robic 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 o xygen (deprotonated), azomethine nitrogen and an ortho carbon atom (de protonated) of the benzaldehyde fragment. The complexes behave as one- electron paramagnets; and give rhombic EPR spectra, that have been ana lysed to furnish values of axial and rhombic distortion parameters as well as the energies of the two expected ligand field transitions with in the t2 shell. One of the transitions has been experimentally observ ed in the predicted region. The complexes are electroactive and displa y ruthenium(III)-ruthenium(II) (E1/2 -0.5 to -0.8 V vs. SCE) and ruthe nium(IV)-ruthenium(III) (E1/2 0.4 to 0.8 V) couples. The E1/2 values v ary linearly with the Hammett constant of the substituent R. The role of phenolato-coordination in stabilizing the trivalent state of ruthen ium is noted.