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

Siqi Zhang,Liang Zhao

doi:10.1038/s41467-019-12889-w

Abstract

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≡CCuI3)-(μ2-OH)-CuII] 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 [CuII-(μ2-OH)-CuII] embedded in a small macrocyclic homologue shows no HAT reactivity. Theoretical calculations indicate that the strong oxidation ability of Cu(II) in [(tBuC≡CCuI3)-(μ2-OH)-CuII] is mainly ascribed to the uneven charge distribution of Cu(I) ions in the tBuC≡CCuI3 unit because of significant [dCu(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.

Highlights

Ubiquitous copper-oxygen species are pivotal in enabling multifarious oxidation reactions in biological and chemical transformations
Inspired by previous synthesis and oxidative reactivity studies of single metal–oxygen species (e.g., Fe(O) and Mn(O) species) stabilized by a size-matched macrocycle36, we expect that macrocyclic compounds with large-sized cavity and flexible conformations may provide a convenient tool to access metal cluster units formed in the Glaser coupling reaction
X-ray crystallographic analysis revealed the formula of this crystalline complex as [Cu4(μ3-tBuC≡C)(μ2-OH)(Py[8])(CH3CN)](BF4)3·2 (CH3OH)·2(H2O) (1), wherein four copper ions are assigned as a CuI3 + CuII combination based on the charge balance requirement and detailed structural characterizations vide infra

Summary

Introduction

Ubiquitous copper-oxygen species are pivotal in enabling multifarious oxidation reactions in biological and chemical transformations. We report the isolation and characterization of the bi-cluster intermediate [(tBuC≡CCuI3)-(μ2-OH)-CuII] from the Glaser coupling reaction by using azacalix[8]pyridine (Py[8]) as a peripherally macrocyclic ligand (Fig. 1).

Results

Conclusion