Kinetics and mechanism of the reaction of chelated Pd(II) complexes with thiols in acidic aqueous solution. Synthesis and crystal structure of [Pd(bpma)Cl]Cl·H_2O (bpma = bis(2-pyridylmethyl)amine)

摘要

The kinetics of the complex-formation reactions between monofunctional palladium(II) complexes [Pd(N-N-N)H_2O]~(2+), where N-N-N is 2,2':6',2"-terpyridine(terpy), diethylenetriamine (dien) or bis(2-pyridylmethyl)amine (bpma), with L-cysteine, DL-penicillamine and glutathione, have been studied in an aqueous 0.01 M perchloric acid medium using variable-temperature and - pressure stopped-flow spectrophotometry. Second-order rate constants, #kappa#_1~(298), varied between 2.8 X 10~2 and 4.4 X 10~4 M~(-1) s~(-1). The highest reactivity was observed for the [Pd(terpy)H_2O]~(2+) complex, whereas glutathione is the strongest nucleophile. Activation volumes for these reactions varied between -5.6 +- 0.3 and -10.7 +- 1.0 cm~3 mol~(-1). The negative entropies and volumes of activation support a strong contribution from bond making in the transition state of the substitution process. The crystal structure of [Pd(bpma)Cl]Cl·H_2O have been determined by X-ray diffraction at 190 K. Crystals are triclinic with space group P1 and consist of distorted of distorted square-planar [Pd(bpma)Cl]~+ cations. The Pd-N distances are all equal to 2.005(7) A.The Pd-Cl distance is 2.305(3) A.