Displacement of neutral nitrogen donors by chloride in [Pt(SNS)(R-py)](ClO4)(2) (SNS=2,6-bis(methylthiomethyl)pyridine; R-py = pyridines): A reactivity comparison between meta- and para-substituted pyridines

摘要

The kinetics of the process [Pt(SNS)(R-py)](2+) + Cl- --> [Pt(SNS)Cl](+) + R-py {SNS=2,6-bis(methylsulfanylmethyl)pyridine; R-py=meta- or para-substituted pyridines covering a wide range of basicity} were studied in methanol at 25 degrees C. The reactions obey the usual two-term rate law observed in the substitution reactions of square-planar d(8) complexes. The plots of log k(2) (k(2) = second-order rate constants) against the pK(a) of the heterocycles conjugate acids highlighted a different sensitivity of the two groups of N-donors to changes in basicity, thepara-substituted pyridines (4R-py) showing a weaker dependence on pK(a) than the meta-substituted (3R-py). The results have been explained on the basis of a pi-acidity difference between 3R-py and 4R-py which influences the reaction ground state. (C) 2008 Elsevier Ltd. All rights reserved.