engleski

A tale of cyclopalladated azobenzene acetates

The direct solid-state mechanochemical (Juribašić et al., Chem. Commun. 2014) or accelerated aging (Monas et al., Chem. Commun. 2016) palladium-mediated activation of strong phenyl C–H bonds by palladium(II) acetate results in mono- or dicyclopalladated complexes. Reactions are quantitative and significantly faster than solution synthesis and allow highly regioselective activation of one or two C–H bonds in asymmetrically substituted azobenzene. Organopalladium products were fully spectroscopically characterized and their structures have been confirmed by X-ray crystallographic structure determination. Mono- and dicyclopalladated complexes are anti dimers with transoid (1A and 2A) or cisoid (2B) geometry in which each palladium atom is bonded in a slightly distorted square-planar geometry to one carbon atom of the phenyl ring, one azo-nitrogen, and two oxygen atoms of the bridging acetate ligands mutually in cis position. The molecular structure of complexes 1A and 2A is dimeric with two monocyclopalladated azobenzene units bonded by two bridging acetate ligands in an anti open-book arrangement. The molecular structure of 2B is a centrosymmetric tetranuclear acetato-bridged complex. It is a unique dimer with two dicyclopalladated azobenzene units forced to lie exactly above one another by four cis-bonded acetate ligands.

C-H activation ; mechanochemistry ; accelerated aging ; palladium ; azobenzene

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