VOLUMES OF ACTIVATION FOR THE SUBSTITUTION-REACTIONS OF CIS-[PTL2(CL)X] AND TRANS-[PTL2(CL)X] WITH PYRIDINE IN VARIOUS SOLVENTS

The pressure dependence of the second-order rate constant for the substitution by pyridine in mjns-[Pt(py)2(Cl)(NO2)] was measured in the solvents nitromethane, methanol, ethanol, and dichloromethane. The respective values were calculated to be -6.2 ± 0.4 at 10 °C, -8.8 ± 0.6 at 25 °C, -13.1 ± 0.8 at 25 °C, and -19.8 ± 1.7 cm3 mol-1 at 25 °C. The ∆V‡expt1 values for the corresponding reactions of cis-[Pt(py)2(Cl) (NO2)] and trans-[Pt(PEt3)2Cl2] in methanol at 25 °C are -5.5 ± 0.5 and -13.6 ± 0.8 cm3 mol-1, respectively. These ∆V‡expt1 were found to be only slightly temperature dependent. The activation parameters ∆H‡2 and ∆S‡2 were also determined for each reaction. The volume change associated with the partial formation of the Pt-py bond was estimated to be -4 ± 1 cm3 mol-1. A qualitative explanation of the solvent dependence of ∆V‡expt1 is also given. © 1979, American Chemical Society. All rights reserved.