Oxidation of tetranuclear copper(I) complexes [(Pip)_nCuX]_4;n = 1 or 2,Pip = Piperidine and X = Cl or Br,with two equivalents of tetrachloro-l,2-benzoquinone (TC1BQ) and sequentional oxidation with one equivalent of TC1BQ followed by dioxygen in apr

摘要

Copper(I) halides react quantitatively with piperidine in dioxygen-free CH_2C1_2 or PhNO_2 to form tetranuclear copper(I) complexes [(pip)_nCuX]_4;n = 1 or 2 and X = Cl or Br.These complexes are very soluble in CH_2C1_2 and PhNO_2 and completely reduce tetrachlorol,2-benzoquinone (TC1BQ) and O_2 to the 3,4,5,6-tetrachlorocatecholato ligand (Cat) and the oxo form.The stable solid complexes [(pip)_nCuX]_4Cat_2 and [(pip)_nCuX]_4CatO are closely related to the intermediate,bridging mu-catecholato complex,which is formed during the mono-oxygenation and oxidation of PhOH by oxytyrosinase.Cryoscopic and analytical data for these complexes indicate that [(pip)_nCuX]_4Cat_2 and [(pip)_nCuX]_4CatO are discrete tetranuclear species.Electronic transition spectra in the near i.r.with high molecular absorptivity are diagnostic for a tetranuclear 'Cu_4X_4' core structure.The electronic transitions are more likely to be due to charge transfer between a minimum of three halo ligands to the copper(II) center.The room temperature e.p.r.spectra of [(pip)_nCuX]_4Cat_2 and [(pip)_nCuX]_4CatO in CH_2C1_2 are isotropic with four hyperfine lines.The room temperature solid state e.p.r.spectra of these complexes show an axial spectra with d_X~2-y~2 ground state,suggesting a square pyramidal arrangement around copper(II) centers in all n = 1 complexes and an elongated tetragonal octahedral arrangement around copper(II) centers in all n = 2 complexes.Cyclic voltammetry measurements show that they are more likely to be irreversible and show slight quasi-reversibility when X = Br and n - 2.Constant potential electrolysis indicate that the number of electrons consumed are equal to four which will be due to the reduction of four copper(II) species to copper(I).