Mechanistic Studies on Fast Ligand-Substitution Reactions of a Very Labile PdII Complex in Several Ionic Liquids

Detailed kinetic studies on the ligand-substitution reactions of the very labile [Pd(terpy)Cl](+) (terpy = 2,2':6',2 ''-terpyridine) complex have been performed for neutral and anionic nucleophiles in several imidazolium-based ionic liquids. The detailed substitution mechanisms derived from the obtained rate and activation parameters differ from those expected on the basis of data aquired in aqueous medium, since the selected ionic liquids significantly affect the nucleophilic attack of the entering ligand on the complex. The rate constant for the substitution reaction with thiourea as entering nucleophile is much larger in water, viz. (7.8 +/- 0.2) x 10(5) M-1 s(-1), than in the ionic liquids [emim][NTf2] and [emim][EtOSO3], viz. (2.5 +/- 0.1) x 10(4) and (1.8 +/- 0.1) x 10(3) M-1 s(-1) at 25 degrees C, respectively, which can be accounted for in terms of the protective interaction of the anionic components of the ionic liquids with the electrophilic metal centre.