Factors Influencing the Formation of Cis and Trans Isomers in Long-Chain Bis(phosphine) Complexes of Platinum(II)

Article abstract of DOI:10.1021/ja00386a028

The square-planar platinum(II) complexes of a series of bis(diphenylphosphine)alkanes have been synthesized and characterized by infrared and phosphorus-31 NMR spectroscopy, elemental analysis, and vapor-phase osmometry.Cis complexes are formed when the complex precursor is potassium tetrachloroplatinate(II), while the corresponding trans complexes are preferred when the starting material is Zeise's salt.An unusual trans-bonded complex with dpe has been isolated.The trans isomers revert to their cis analogues in the presence of heat or excess bis(phosphine).The cis dimers are the most stable isomers for the majority of the cis complexes.The preferred ring sizes for the cis chelated monomers are 14- and 19-membered chelate rings.The amount of trans monomer increases with increasing chain length and reaches a maximum with a chelate ring size of 15 members and can be correlated directly with ring contributions to the chemical shift - thus ring contributions in trans monomeric complexes can be used as a measure of ring strain for these ligands.Large flexible chelate rings (19 members or above) appear to be unstable in the configuration.