Crystal Structures and Acetonitrile Exchange of Palladium(II) Complexes with Bis(3-aminopropyl)amine and Diethylenetriamine. Effects of Ion-Pair Formation

Abstract

Abstract The crystal structures of palladium(II) complexes with tridentate amine and acetonitrile, [Pd(CH3CN)(dptn)](CF3SO3)2 (1) and [Pd(CH3CN)(dien)](CF3SO3)2 (2) (dptn = bis(3-aminopropyl)amine and dien = diethylenetriamine), have been determined by X-ray crystal structure analysis. The central palladium(II) ion has a distorted square-planar geometry. The five-membered chelate rings of the dien ligand in 2 are more strained than the six-membered chelate rings of the dptn ligand in 1, as indicated from the difference in the angles of terminal N–Pd–terminal N and the averaged Pd–N–C angles around the terminal nitrogens. The kinetics of acetonitrile exchange of 1, 2, and [Pd(CH3CN)(dien)](BF4)2 (3) have been investigated by the 1H NMR line-broadening technique. The observed rate constants can be expressed by kobs = k1 + k2 [CH3CN] from the dependence of kobs on the acetonitrile concentration. It has been indicated that the k1 and k2 paths proceed via the dissociative and associative modes of activation, respectively. The dissociative k1 path is promoted by the ion-pair formation where the bound ligand effect is enhanced by the electrostatic interaction between the counter anions and amine protons. The reaction mechanisms are discussed in terms of the steric and electronic factors of the bound ligands (dptn and dien) and the effect of the ion-pair formation with the counter anions (CF3SO3− and BF4−).