Valence specific chelation of ruthenium to Schiff mono-bases of 2,6-diformyl-4-methylphenol: Synthesis and structure of trivalent salicylaldiminato species of coordination type RuN2O2PCl

The reaction of Schiff mono-bases, HRL (R = Me, Et), of 2,6-diformyl-4-methylphenol with K-2 RuCl5(H2O) has afforded Ru-III(RL)(2)(PPh3)Cl. The X-ray structure of the R = Et complex has revealed metal chelation at the salicylaldimine segment of RL-, the two phenolic oxygen and azomethine nitrogen atoms lying in mutually trans and cis positions, respectively. The trivalent state of the metal is stabilized in Ru(RL)(2)(P-Ph-3)Cl, the ruthenium(III)/ruthenium(II) E-1/2 being similar to 0.40 V as SCE. These distorted low-spin (t(2)(5)) complexes display rhombic EPR spectra and are characterized by a pair of ligand field transitions (in the near-IR region) within the split t(2) shell. The complexes provide a striking contrast with the ruthenium(II) organometallics arising from the reaction of HRL with Ru-II(PPh3)(3)Cl-2. (C) 1997 Elsevier Science Ltd.