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(11) 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 degreesC 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)I(ClO4)(2) has been determined by X-ray diffraction. Crystals are triclinic, space group P (1) over bar, 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 Angstrom and significantly shorter than any of the other M-N distances. The pyridine plane forms a dihedral angle of 61.9(2)degrees with the coordination N4 donors. (C) 2004 Elsevier B.V. All rights reserved.