Secondary Sphere Hydrogen Bonding in Monocopper Complexes of Potentially Dinucleating Bis(carboxamide) Ligands

A merged copper(I/II) cluster isolated from Glaser coupling

Ubiquitous copper-oxygen species are pivotal in enabling multifarious oxidation reactions in biological and chemical transformations. We herein construct a macrocycle-protected mixed-valence cluster [(^tBuC≡CCu^I₃)-(μ₂-OH)-Cu^II] by merging a copper acetylide cluster with a copper-oxygen moiety formed in Glaser coupling. This merged Cu(I/II) cluster shows remarkably strong oxidation capacity, whose reduction potential is among the most positive for Cu(II) and even comparable with some Cu(III) species. Consequently, the cluster exhibits high hydrogen atom transfer (HAT) reactivity with inert hydrocarbons. In contrast, the degraded [Cu^II-(μ₂-OH)-Cu^II] embedded in a small macrocyclic homologue shows no HAT reactivity. Theoretical calculations indicate that the strong oxidation ability of Cu(II) in [(^tBuC≡CCu^I₃)-(μ₂-OH)-Cu^II] is mainly ascribed to the uneven charge distribution of Cu(I) ions in the ^tBuC≡CCu^I₃ unit because of significant [d_Cu(I) → π*_(C≡C)] back donation. The present study on in situ formed metal clusters opens a broad prospect for mechanistic studies of Cu-based catalytic reactions.

Copper-oxygen species in organometallic complexes and enzymes are involved in many oxidation reactions. Here, the authors synthesize a macrocycle-protected mixed valence Cu(I/II) cluster with an unusually strong oxidation capacity and apply it to hydrogen atom transfer reactions with inert hydrocarbons.

The wonderful world of pyridine-2,6-dicarboxamide based scaffolds

This perspective focusses on a variety of scaffolds based on a pyridine-2,6-dicarboxamide fragment and their noteworthy roles in coordination chemistry, biomimetic studies, catalysis, and sensing.