(3-Chloro-2-methylenecycloalkyl)palladium Chloride Dimers: Preparation, Conformation, and Fluxional behavior
American Chemical Society
The title compounds are prepared in nearly quantitative yields by the reaction of -methylenebicyclo[n.l.O]alkanes with bis(acetonitrile)palladium chloride. The C3 configuration and ring conformation of the (3-chloro-2-methylenecycloalkyl)palladium chloride dimers are assigned from their and 13C NMR spectra. The chloropalladation of exo-3-methylenetricyclo[3.2.1.02,4]octane provides positive evidence for the addition of Cl to the sterically less hindered face of the methylenecyclopropane precursor. The kinetic products of the proposed cis-chloropalladation mechanism may undergo 1 23—* 1 5—* 3 isomerization at the unsubstituted allyl terminus to afford the thermodynamically stable isomers. Allylic strain is shown to be an important factor in the relative stability of the (1-substituted 3-chloro-2-methylenecycloheptyl)- palladium chloride 3 -*· 1 -*· 3 diastereomers. Preparation of the title compounds with ring size >9 allows assessment of the factors involved in syn-anti isomerization at the endocyclic terminus of exocyclic x-allyl complexes. For the medium to large ring complexes the results indicate that ring strain, torsional strain, and transannular nonbonding repulsions greatly contribute to the relative stabilities of the syn and anti isomers.