Kinetics and mechanism of the complex formation of [Pd(NNN)Cl]+ with pyridines in methanol: synthesis and crystal structure of [Pd(terpy)(py)](ClO4)2

The kinetics of the complex-formation reactions between monofunctional palladium(II) complexes [Pd(NNN)Cl]+, where NNN is 2,2′:6′,2″-terpyridine (terpy), diethylenetriamine (dien) or bis(2-pyridylmethyl)amine (bpma), with pyridine, 4-methylpyridine, 4-acetylpyridine, 4-cyanopyridine and 4-aminopyridine, have been studied in methanol at 25 °C using stopped-flow spectrophotometry. The highest reactivity was observed for the [Pd(terpy)Cl]+ complex, whereas 4-aminopyridine is the strongest nucleophile. The results, compared with those previously published on the [Pt(NNN)Cl]+ complexes, are discussed in terms of reactivity and discrimination ability of the reaction centre. The crystal structure of [Pd(terpy)(py)](ClO4)2 has been determined by X-ray diffraction. Crystals are triclinic, space group , and consist of distorted square planar [Pd(terpy)(py)]2+ cations and perchlorate anions. The Pd–N bond length to the central atom of terpy ligand is well below 2.0 Å and significantly shorter than any of the other M–N distances. The pyridine plane forms a dihedral angle of 61.9(2)° with the coordination N4 donors.