Dimeric Copper(I) Complex with a Disulfonamide-Bridged Core

Pyridine-2-yl-sulfonyl-quinolin-8-yl-amide (psq) has produced the first sulfonamidato-bridged dicopper(I) complex, {Cu[κ⁴-(μ-κN:κN-psq)]}₂ containing the rhombic Cu(I)₂N₂ core. The single crystal X-ray structure of this complex shows that two anionic psq ligands straddle the metal atoms via bridging sulfonamide N atoms to give a Cu···Cu distance of 2.9593(8) Å. When it is dissolved in chloroform [Cu(psq)]₂ activates C–Cl bonds as demonstrated through the rapid formation of [CuCl(psq)]₂. While the solid orange compound is stable for weeks under N₂. Acetonitrile solutions of [Cu(psq)]₂ are rapidly oxidized in air. A 1D-carbonato-bridged coordination polymer, {Cu₂[κ⁴-(μ-κO:κN-psq)]₂[μ₃-CO₃][H₂O]}, and the bis-homoleptic complex [Cu(κ³-psq)(κ²-psq)] are concurrently isolated in high yield without evidence of ligand oxidation with H₂O₂ detected as a side product. This implicit O₂ activation was harnessed in the oxidation of phenol substrates. 2,6-Di-tert-butylphenol is catalytically converted to the coupled dione product with 100% yield. If a para-blocked phenol is used, the reaction become stoichiometric and an O₂-derived hydroperoxide group is installed into the ortho position. In contrast, nitrophenol is not oxidized and the result is metal-based oxidation and isolation of [Cu(OC₆H₄NO₂)(psq)]₂. This is rationalized by this more acidic phenol acting as a proton donor, rather than a H atom donor to a putative O₂ adduct.