cis-Divinylcyclopropane and the hexafluoroacetylacetonatorhodium(I) complexes of cis- and trans-divinylcyclopropane

Abstract

The synthesis of cis-divinylcyclopropane has been achieved by Wittig reaction of cis-2-vinylcyclopropanecarbaldehyde with methylenetriphenylphosphorane at 5°. The product is stable at low temperatures, and rearranges quantitatively to cyclohepta-1,4-diene with a half-life of 11 min at 288.5 K. An approximate set of reaction rate measurements in CFCl₃ shows that ΔG^‡= 86 kJ mol^–1. cis-Divinylcyclopropane reacts with bisethylenehexafluoroacetylacetonatorhodium(I) in isopentane to give a 1 : 1 complex with displacement of ethylene which is thermally stable for moderate periods at 65°, rearranging slowly to the hexafluoroacetylacetonatorhodium(I) complex of cyclohepta-1,4-diene. Spectroscopic evidence suggests that this former species has an intact cyclopropane ring. In contrast, trans-divinylcyclopropane reacts with bisethylenehexafluoroacetylacetonatorhodium(I) giving a 1 : 1 complex in which the cyclopropane ring has opened to form a bis-π-allylrhodium complex.