Ortho–Ortho Selective Oxidative Coupling of Phenols by Hydroxo Multicopper(II) Clusters

An ortho–ortho selective aerobic oxidative coupling
of unsubstituted,
mono- and poly substituted phenols that have been considered beyond
the scope of oxidative coupling reactions is reported. The simple
conditions involve mixing a phenol with the readily available hydroxo
multicopper clusters, particularly the [Cu(tmeda)(μ-OH)]2(ClO4)2 complex, in 1,1,1,3,3,3-hexafluoropropan-2-ol
(HFIP). The unprecedented site selectivity is rationalized by the
ability of the dicopper complex to bring the two phenolate ligands
in proximity to react at the less hindered ortho position. DFT calculations,
high-resolution mass spectroscopy, and Infrared photodissociation
(IRPD) spectroscopy were applied to reveal key aspects of the reaction.