The reaction of metal-ion complexes with hydrocarbons. Part 4. Formation of complexes of the types di-µ-acetato-bis[(η3-allyl)palladium] and tetra-µ-acetato-di(η3-allyl)tripalladium by reaction of mono-olefins and 1,3-dienes with palladium acetate

Abstract

Trimericpalladiumacetate, [Pd₃(O₂CMe)₆], reacts with mono-olefins such as cyclohexene, hex-1-ene, cis-hex-2-ene, oct-1-ene, cis-pent-2-ene. propene, and 2,3,3-trimethylbut-1-ene in acetic acid solution by loss of acetic acid and with formation of [Pd₃(η³-allyl)₂(µ-O₂CMe)₄] which reacts further to yield [Pd₂(η³-allyl)₂(µ-O₂CMe)₂]. Perchloric acid catalyses these reactions, suggesting that they involve electrophilic attack of Pd^II on the olefin with loss of a proton from the allylic carbon. The ¹H and ¹³C n.m.r. spectra in CDCl₃, solution show that the complexes are fluxional due to the acetate-bridging arrangement which allows. interconversion of different conformations of the allyl group. Exchange experiments with acetic acid show that Pd–O bonds trans to the allyl group are more labile than those attached to the central palladium with four oxygen donors in the trinuclear complex. Hexa-2,4-diene undergoes an addition reaction with [Pd₃(O₂CMe)₆] to yield di-µ-acetato-bis[(2–4-η-5-acetoxyhex-2-enyl)-palladium] which also yields a trinuclear complex on further reaction with [Pd₃(O₂CMe)₆]. N.m.r. spectra show that this binuclear complex exchanges with acetic acid in CDCl₃ solution, the µ-acetate being more labile to exchange than the organic acetate, while the trinuclear complex does not exchange under these conditions.