Normal- and high-pressure kinetics and mechanism of the cis-trans isomerization of PtXR(PEt3)2 complexes. Evidence for an initial solvolysis step

Article abstract of DOI:10.1021/ic50206a011

It has been previously postulated that the spontaneous cis-trans isomerization of PtXR(PEt₃)₂, where R = alkyl or aryl groups and X = halides, occurs through the three-coordinate intermediate PtR(PEt₃)₂⁺, which is in a steady state during the reaction. High-pressure kinetics have now revealed a ΔV^≠ value of-12 cm³ mol^-1 for the first step in this mechanism. Therefore this step must be considered to be associative. Kinetics at atmospheric pressure show that the intermediate species is not in a steady state, but rather a preequilibrium exists. These data are consistent with an initial solvolysis step and also establish that the rate of solvolysis of cis-PtXR(PEt₃)₂ is faster than the rate of the subsequent isomerization reaction. A ΔV^≠ value of +7.7 cm³ mol^-1 was found for the isomerization reaction. This can be interpreted either as a dissociation of the intermediate cis-PtR(MeOH)(PEt₃)₂ or as an intramolecular rearrangement of this species.