Steric and electronic tuning of the reactivity of [RuII(terpy)(NN)Cl]Cl complexes

The substitution behavior of [Ru-II(terpy)(phen)Cl]Cl and [Ru-II(terpy)(tmen)Cl]ClO4 (where terpy = 2,2':6',2 ''-terpyridine, phen = 1,10-phennatroline, tmen = N,N,N',N'-tetramethylethylenediamine) have been investigated. The crystal structures of the complexes were determined by single crystal X-ray diffraction. The structures of the complexes in solution were confirmed by ESI-MS and multinuclear NMR spectroscopy. The stability of [Ru-II(terpy)(phen)Cl]+ and [Ru-II(terpy)(tmen)Cl](+) in aqueous solution, acidity and substitution behavior of the corresponding aqua derivatives with chloride, thiourea and N,N'-dimethylthiourea, were studied. The kinetics of the substitution reactions was followed under pseudo-first order conditions using UV-visible spectroscopy as a function of nucleophile concentration and temperature. The reactivity and pK(a) values of the tmen and phen complexes were compared with the earlier studied Ru(II) polypyridine complexes. The aqueous behavior of all the examined Ru(II) complexes depends on the electronic and steric properties provided by the spectator bidentate ligands.