Abstract
Kinetic studies of ligand substitutions of the six-coordinated Ru-II pseudo-macrocyclic complex [Ru(CHDH)(2)-(PPh3)(2)] (CHDH = cyclohexanedione-dioximato) have been spectrophotometrically investigated in a variety of solvents and at 70, 80, 85 and 90 degrees C. The reactions studied are of the form:
[(PPh3)Ru(CHDH)(2)(PPh3)] + L = [(PPh3)Ru(CHDH)(2)L] + PPH3
where L is imidazole, pyridine, piperidine or thiophene or a solvent molecule (PhCl, PhMe, MeCN, DMSO or DMF). The solvolysis reactions with chlorobenzene and toluene proceed to an equilibrium position favoring the bis-triphenylphosphine complex. All other reactions proceed to completion. From a mechanistic point of view the reactions were found to proceed through the formation of a five coordinate intermediate that possesses little or no discriminating ability towards the incoming nucleophiles. The rate data were thus interpreted in terms of a dissociative (D) or dissociative interchange (Id) mechanism. Activation parameters Delta H double dagger and Delta S double dagger are reported. Preliminary studies on the solvatochromic behavior of [Ru(CHDH)(2)(PPh3)(2)] and the corresponding mixed complexes are discussed.