Palladium(II) halide complexes. III. Acid hydrolyses and halide anations of cis- and trans-dichlorodiaquapalladium(II) and -dibromodiaquapalladium(II)

Abstract

Chloride and bromide anations of PdX(H 2O) 3 +, cis-PdX 2(H 2O) 2 and trans-PdX 2(H 2O) 2, acid hydrolyses of PdX 3H 2O −, cis-PdX 2(H 2O) 2 and trans-PcX 2(H 2O) 2, X = Cl, Br, have been studied at different temperatures by means of a stopped-flow technique. Rate constants are given in Tables V and VII, activation parameters in Table VII. The palladium complexes react about 5×10 4 to 5×10 5 times faster than the analogous platinum(II) complexes. The activation enthalpies are 8 to 10 kcal mol −1 smaller for palladium. A simple model for description of the rates of acid hydrolyses and halide anations of palladium(II) and platinum(II) halide complexes by cis-, trans-, and ionic charge effects is introduced. For palladium, the relative trans-effect Cl/H 2O is about 50 and Br/H 2O about 500. The relative cis-effect H 2O/ Cl is about 4 and H 2O/Br about 8. The trans-effects are 6 times smaller than for corresponding platinum complexes, the cis-effects somewhat greater. The equilibrium between cis-PdX 2(H 2O) 2 and trans-PdX 2(H 2O) 2 has been studied. The cis-isomer is the dominant species at equilibrium, the equilibrium constant cis/trans being 2.1±0.3 for X = Cl and 6.0± 0.8 for X = Br at 25°C. The ionic strength was 1.00 M and the supporting electrolyte perchloric acid.