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

Huynh MHV; Lasker JM; Wetzler M; Mort B; Szczepura LF; Witham LM; Cintron JM; Marschilok AC; Ackerman LJ; Castellano RK; Jameson DL; Churchill MR; Jircitano AJ; Takeuchi KJ

Journal of the American Chemical Society, Vol.123, No.36, 8780-8784, 2001

DOI10.1021/ja0041977 Export Citation

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

Huynh MHV, Lasker JM, Wetzler M, Mort B, Szczepura LF, Witham LM, Cintron JM, Marschilok AC, Ackerman LJ, Castellano RK, Jameson DL, Churchill MR, Jircitano AJ, Takeuchi KJ

The influence of two different di(I-pyrazolyl)alkane ligands on the rate constant of aqua ligand substitution of ruthenium(II) complexes with the formula [Ru(H2O)(L-2)(tpmm)](2+) (L-2 = di(I-pyrazolyl)methane (DPMet) or 2,2-di(I-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)(L-2)(tpmm)](+). These results are discussed in the context of a heteroscorpionate effect exerted by the DPPro ligand.