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Evidence for (π-allyl)palladium(II)(quinone) complexes in the palladium-catalyzed 1,4-diacetoxylation of conjugated dienes

✍ Scribed by Jan-E. Báckvall; Adolf Gogoll

Publisher
Elsevier Science
Year
1988
Tongue
French
Weight
269 KB
Volume
29
Category
Article
ISSN
0040-4039

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✦ Synopsis

Evidence for a coordination of p-benxoquinone to palladium in [4-acetoxy-n3-(1,2,3)-cyclohexenyllpalladium(II) complexes was provided by changes of the 'H NMR chemical shift values of the r-ally1 protons and a decrease of the spin-lattice relaxation time constant for the p-benxoquinone protons. We have recently developed a number of methods for palladium-catalyzed 1,4-oxidations of conjugated dienes.' In all these oxidations, which proceed via (n-allyl)palladium complexes, p-benxoquinone plays a key role as electron transfer mediator (eq. 1). Although kinetic studies suggest formation of (~-allyl)palladium(II)-(benxoquinone) complexes as intermediates in the quinone induced nucleophilic addition.'* 24 2c direct evidence for their existence is' still lacking.3 In this communication we report for the first time the detection of p-benzoquinone-and 1.4-naphthoquinone-(rr-allyl)palladium(II)complexes by NMR specttoscopy.

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