Reactions of co-ordinated ligands. Part XI. The ring opening of methylenecyclopropanes by palladium(II)–nucleophile systems: formation of substituted η3-but-3-enyl complexes of palladium(II)

Abstract

trans- and cis-2,3-Dimethoxycarbonylmethylenecyclopropanes react with [Pd(MeCN)₂Cl₂] in dichloromethane to yield isomeric, ring-opened η³-[3-chloro-1,2-bis(methoxycarbonyl)but-3-enyl]palladium(II) complexes, via[Pd(η²-methylenecyclopropane)Cl₂] intermediates. Analogous reactions in methanol, ethanol, isopropyl alcohol, and t-butyl alcohol solvents yield isomeric η³-[4-alkoxy-l,2-bis(methoxycarbonyl)but-3-enyl]palladium(II) complexes. ¹H and ¹³C N.m.r. data for these, and derived, complexes are reported and discussed in terms of conformational isomerism within the chelating but-3-enyl ring. The mechanisms of these ring-opening reactions are discussed in terms of substituted cyclopropylmethyl-palladium intermediates, and the implications with respect to the mechanisms of chloropalladation and alkoxypalladation reactions of olefins are also reviewed.