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.