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
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 PdII 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.