Add time:08/27/2019         Source:sciencedirect.com

Copper(I) bromide dissolves in deoxygenated methylene chloride and nitrobenzene solutions of equimolar N,N′- diethylethylenediamine (DEED) to give the colorless copper(I) dimer [(DEED)CuBr]2 (D). Dioxygen uptake, analytical, cryoscopic, spectral and kinetic data show that D is oxidized to the blue tetranuclear mixed valence peroxocomplex [(DEED)CuBr]4O2 (A) at temperatures from -51 to 30 °C. The rate law is d[A]/dt=koL[O2][D]2 with activation parameters δH≠DL=-1.8±0.4 kcal mol−1 and δSYL=-38±5 cal deg−1 mol−1 at 25 °C. These parameters resemble those for third-order oxidation of the copper(I) dimer [(TEED)CuCI]2 (TEED is N, N, N′, N′- tetraethylethylenediamine) to the peroxocopper product [(TEED)CuCI]4O2 at low temperatures. They are completely different from those for direct, third-order oxidation of [LCuX]2 dimers to the oxocopper(II) products [LCuX]2O at ambient temperatures because of slow transfer of the third electron from copper(I) to O2 in ambient [(DEED)CuBr]2/O2 and low temperature [(TEED)CuCI]2/O2 reactions. As observed in the [(TEED)CuCI]2/O2 system, primary product A relaxes to a different tetranuclear copper complex B, with A thermodynamically favored at higher temperatures up to - 17 °C. First-order decomposition of A to give 2 mol of the oxocopper(II) product [(DEED)CuBr]2O (C) has an exceptionally long half-life of 3.2 ± 0.1 h at 25 °C. The resistance of A to intramolecular copper(I)→ peroxide electron transfer with L=DEED and X=Br is attributed to (i) hydrogen bonding between the NH groups of DEED and bound peroxide and (ii) stabilization of copper(I) by Br.

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