title: Palladium(II) complexes with highly basic imidazolin-2-imines and their reactivity toward small bio-molecules.
abstract: A series of novel Pd(ii) complexes with chelating mono(imidazolin-2-imine) and bis(imidazolin-2-imine) ligands were synthesized. The crystal structures of [Pd(DMEAIm(iPr))Cl2] and [Pd(DPENIm(iPr))Cl2] were determined by X-ray diffraction analysis. The reactivity of the six Pd(ii) complexes, namely, [Pd(en)Cl2], [Pd(EAIm(iPr))Cl2], [Pd(DMEAIm(iPr))Cl2], [Pd(DPENIm(iPr))Cl2], [Pd(BL(iPr))Cl2] and [Pd(DACH(Im(iPr))2)Cl2], were investigated. Spectrophotometric acid-base titrations were performed to determine the pKa values of the coordinated water molecules in [Pd(en)(H2O)2](2+), [Pd(EAIm(iPr))(H2O)2](2+), [Pd(DMEAIm(iPr))(H2O)2](2+), [Pd(DPENIm(iPr))(H2O)2](2+), [Pd(BL(iPr))(H2O)2](2+) and [Pd(DACH(Im(iPr))2)(H2O)2](2+). The substitution of the chloride ligands in these complexes by TU, l-Met, l-His and Gly was studied under pseudo-first-order conditions as a function of the nucleophile concentration and temperature using stopped-flow techniques; the sulfur-donor nucleophiles have shown better reactivity than nitrogen-donor nucleophiles. The obtained results indicate that there is a clear correlation between the nature of the imidazolin-2-imine ligands and the acid-base characteristics and reactivity of the resulting Pd(ii) complexes; the order of reactivity of the investigated Pd(ii) complexes is: [Pd(en)Cl2] > [Pd(EAIm(iPr))Cl2] > [Pd(DMEAIm(iPr))Cl2] > [Pd(DPENIm(iPr))Cl2] > [Pd(BL(iPr))Cl2] > [Pd(DACH(Im(iPr))2)Cl2]. The solubility measurements revealed good solubility of the studied imidazolin-2-imine complexes in water, despite the fact that these Pd(ii) complexes are neutral complexes. Based on the performed studies, three unusual features of the novel imidazolin-2-imine Pd(ii) complexes are observed, that is, good solubility in water, very low reactivity and high pKa values. The coordination geometries around the palladium atoms are distorted square-planar; the [Pd(DMEAIm(iPr))Cl2] complex displays Pd-N distances of 2.013(2) and 2.076(2) Å, while the [Pd(DPENIm(iPr))Cl2] complex displays similar Pd-N distances of 2.034(4) and 2.038(3) Å. The studied systems are of interest because little is known about the substitution behavior of imidazolin-2-imine Pd(ii) complexes with bio-molecules under physiological conditions.
authors.affiliation: Department of Chemistry, Faculty of Science, University of Kragujevac, R. Domanovića 12, P. O. Box 60, 34000 Kragujevac, Serbia. bugarcic@kg.ac.rs.
authors.forename: Jovana
authors.initials: J
authors.lastname: Bogojeski
authors.forename: Jeroen
authors.initials: J
authors.lastname: Volbeda
authors.forename: Matthias
authors.initials: M
authors.lastname: Freytag
authors.forename: Matthias
authors.initials: M
authors.lastname: Tamm
authors.forename: Živadin D
authors.initials: ŽD
authors.lastname: Bugarčić
mesh_terms: D048289:Imidazolidines / Q000737:chemistry* / Q000378:metabolism; D007097:Imines / Q000737:chemistry* / Q000378:metabolism; D010165:Palladium / Q000737:chemistry* / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D048289:Imidazolidines; D007097:Imines; D010165:Palladium