Remarkable spectator ligand effect on the rate constant of ligand substitution of (aqua)ruthenium(II) complexes

M H Huynh; J M Lasker; M Wetzler; B Mort; L F Szczepura; L M Witham; J M Cintron; A C Marschilok; L J Ackerman; R K Castellano; D L Jameson; M R Churchill; A J Jircitano; K J Takeuchi

doi:10.1021/ja0041977

Remarkable spectator ligand effect on the rate constant of ligand substitution of (aqua)ruthenium(II) complexes

J Am Chem Soc. 2001 Sep 12;123(36):8780-4. doi: 10.1021/ja0041977.

Authors

M H Huynh¹, J M Lasker, M Wetzler, B Mort, L F Szczepura, L M Witham, J M Cintron, A C Marschilok, L J Ackerman, R K Castellano, D L Jameson, M R Churchill, A J Jircitano, K J Takeuchi

Affiliation

¹ Chemistry Department, State University of New York at Buffalo, Buffalo, New York 14260, USA. huynh@lanl.gov

PMID: 11535083
DOI: 10.1021/ja0041977

Abstract

The influence of two different di(1-pyrazolyl)alkane ligands on the rate constant of aqua ligand substitution of ruthenium(II) complexes with the formula [Ru(H2O)(L2)(tpmm)]2+ (L2 = di(1-pyrazolyl)methane (DPMet) or 2,2-di(1-pyrazolyl)propane (DPPro)) was investigated. A 9.4 x 10(5)-fold increase in the rate constant of ligand substitution at pH = 6.86 was observed when DPMet was replaced with DPPro. This remarkable increase was unexpected, considering that these bidentate ligands appear quite similar. To help lend insight into this dramatic spectator ligand effect, the activation parameters for the ligand substitution reactions were determined, and single-crystal X-ray data were collected on the structurally analogous (chloro)ruthenium(II) complexes, [Ru(Cl)(L2)(tpmm)]+. These results are discussed in the context of a heteroscorpionate effect exerted by the DPPro ligand.