Observations on the Mechanism of Halogen-Bridge Cleavage by Unidentate Ligands in Square Planar Palladium and Platinum Complexes

Cyclo-palladation and - platination of nitrogen donor ligands lead to insoluble μ- chloro dimers which give μ- bromo and μ- iodo dimers on metathesis with the appropriate lithium halide. Addition of pyridine or 2,6-dimethylpyridine to the cyclopalladated dimers gives monomeric complexes with the halogen trans to the metal-carbon bond, whereas addition of 2,6-dimethylpyridine to the cycloplatinated complexes gives the isomer with the halogen cis to the metal-carbon bond. The results are discussed in terms of the mechanism of the bridge cleavage reaction.