REACTIONS AND PROPERTIES OF SOME TRIMETHYLENEPLATINUM(IV) COMPLEXES .6. SKELETAL ISOMERIZATION OF PLATINACYCLOBUTANES AND ITS RELEVANCE TO THE MECHANISM OF OLEFIN METATHESIS

Skeletal isomerization of platinacyclobutane complexes is demonstrated, of the general form [PtCl2(CHRCH2CH2)L2](III)⇌[PtCl2(CH2CHRCH2)L2] (IV), R = aryl; L = nitrogen-donor ligand or tetrahydrofuran. Factors influencing the magnitude of the equilibrium constants for the reactions are discussed and steric effects are found to be dominant in favoring isomer IV, Isomerization is retarded by added ligand L and, when R = 4-tolyl and L = pyridine, the approach to equilibrium follows first-order kinetics and a linear correlation between the reciprocal of the observed rate constants and [C5H5N] is demonstrated. A mechanism involving reversible dissociation of ligand, L, followed by skeletal isomerization of the resulting five-coordinate platinum(lV) complex is proposed. The relevance of this work to the mechanism of olefin metathesis is discussed. Methods of characterization of isomeric platinacyclobutanes using 13C and 1H N MR spectroscopy are presented. © 1979, American Chemical Society. All rights reserved.