Solvent Paths for Square-Planar Substitutions: Part 2. Reactions between Aqua Chloro-Platinates(II) and Ethene

The kinetics for the reactions between the complexes PtCln(H2O)4-n 2−n, n = 0,1,2,3,4, (including cis- and trans-isomers for n = 2) and ethene have been studied. In the case of trans-PtCl2(H2O)2, product analysis shows that both the chloride ligand and the aqua ligand are substituted by ethene in two parallel paths, differing in rate by a factor of 1.5 only. The experiments show that ethene, and probably olefins in general, are inefficient entering ligands, similar to dimethyl sulfoxide. Steric reasons might be responsible. Changes in relative cis- and trans-effects are compatible with an associative mechanism. The aqua complexes are sufficiently reactive with ethene to be steady-state intermediates in associative solvent paths. Reaction models and rate laws for associative square-planar substitutions are discussed, with special reference to reported non-reactivity of solvento intermediates in some previously studied systems.