Synthesis, structure and dioxygen reactivity of a bis(µ-iodo)dicopper(i) complex supported by the [N-(3,5-di-tert-butyl-2-hydroxybenzyl)-N,N-di-(2-pyridylmethyl)]amine ligand

Abstract

The air-sensitive bis(µ-iodo)dicopper(I) complex 1 supported by [N-(3,5-di-tert-butyl-2-hydroxybenzyl)-N,N-di-(2-pyridylmethyl)]amine (L) has been prepared by treating copper(I) iodide with L in anhydrous THF. Compound 1 crystallizes as a dimer in space group C2/c. Each copper(I) center has distorted tetrahedral N₂I₂ coordination geometry with Cu–N(pyridyl) distances 2.061(3) and 2.063(3) Å, Cu–I distances 2.6162(5) and 2.7817(5) and a Cu⋯Cu distance of 2.9086(8) Å. Complex 1 is rapidly oxidized by dioxygen in CH₂Cl₂ with a 1 : 1 stoichiometry giving the bis(µ-iodo)peroxodicopper(II) complex [Cu(L)(µ-I)]₂O₂ (2). The reaction of 1 with dioxygen has been characterized by UV-vis, mass spectrometry, EPR and Cu K-edge X-ray absorption spectroscopy at low temperature (193 K) and above. The mass spectrometry and low temperature EPR measurements suggested an equilibrium between the bis(µ-iodo)peroxodicopper(II) complex 2 and its dimer, namely, the tetranuclear (peroxodicopper(II))₂ complex [Cu(L)(µ-I)]₄O₄ (2′). Complex 2 undergoes an effective oxo-transfer reaction converting PPh₃ into OPPh₃ under anaerobic conditions. At sufficiently high concentration of PPh₃, the oxygen atom transfer from 2 to PPh₃ was followed by the formation of [Cu(PPh₃)₃I]. The dioxygen reactivity of 1 was compared with that known for other halo(amine)copper(I) dimers.