Platinacyclobutanes skeletal isomerization

The rearrangement of platinacyclobutanes to alkene complexes or ylide complexes is shown to involve an initial 1,3-hydride shift (a-elimina-tion), which may be preceded by skeletal isomerization. This isomerization can be used as a model for the bond shift mechanism of isomerization of alkanes by platinum metal, while the a-elimination also suggests a possible new mechanism for alkene polymerisation. New platinacyclobutanes with -CH2 0SC>2Me substituents undergo solvolysis with ring expansion to platinacyclopentane derivatives, the first examples of metallacyclobutane to metallacyclopentane ring expansion. The mechanism, which may also involve preliminary skeletal isomerization, has been elucidated by use of isotopic labelling and kinetic studies. 

Our first observations related to the particular skeletal isomerization of Scheme I were obtained in a study of steric effects of ligands on the stability of platinacyclobutanes (9). Three products could be obtained as shown in equation 2. 

III) at -10°C. The mechanism shown in Scheme II was therefore suggested, involving skeletal isomerization and a-elimination from the platinacyclobutane. 

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