A NOVEL NON-INNOCENT LIGAND REGULARIZES A FORMAL PALLADIUM(I) COMPLEX TO PALLADIUM(II)

In the attempt to generate a palladium/phenanthroline complexes with an 2-ArNO ligands preventing following reactions of the formed complex with excess nitrosoarene, we recently attempted to generate the desired complex by reaction of a palladium(II) precursor, Pd(Phen)(OAc)2, with p-cyanophenyl hydroxylamine. However, instead of the desired complex, a new paramagnetic complex was obtained and crystallographically characterized, in which two hydroxylamine-derived moieties have coupled to give an amido-nitrosoarene ligand. Considering the nitrosoarene as a neutral ligand and the amino group as an anionic one, as it is usually done, the complex would be a very rare example of monomeric palladium(I) complex. However, magnetic measurements and extensive theoretical calculations have shown that the unpaired electron actually resides on the nitroso group and the complex must be regarded as a palladium(II) complex with a radical dianionic ligand. Other arylhydroxylamines react in the same way, but when an o,o-disubstituted hydroxylamine was employed, no reaction was observed.