Copper(I) tris(pyrazolyl)methane complexes and their reactivity towards dioxygen

The reactivity towards dioxygen has been explored for two copper(I) tris(pyrazolyl)-methane complexes, [CuI((3,5-Me2-pz)3CH)(MeCN)](PF6)2 (1) and [CuI((3,5-Me2-4-Br-pz)3)(MeCN)](PF6)2 (2). Reversible oxygenation of 1 occurs in CH2Cl2 solution at ∼7 °C to yield a 2:1 μ-η2η2-peroxo complex [((3,5-Me2-pz)3CH)2Cu2(μ-O2)](PF6)2. Equilibrium studies, made using manometric techniques over the temperature range 258–278 K and at two equilibration times, 2 and 30 min, yielded best-fit thermodynamic constants of K21=32 M−2 (at 298 K), ΔH°=−110±5 K J mol−1, ΔS°=−340±18 J K−1 mol−1 (30 min) which have been compared to values for other CuO2 adducts. Thermal decomposition of this μ-peroxo species yields crystals of a di-μ-hydroxo complex [((3,5-Me2-pz)3CH)2Cu2(μ-OH)2](PF6)2 (3), whose crystal structure and magnetism (J=−298 cm−1) are described. Complex 3 can also be made by reaction of 1 with iodosylbenzene. Complex 2 does not form a dioxygen adduct but slowly oxidizes in CH2Cl2 to form [CuII((3,5-Me2-4-Br-pz)3CH)2](PF6)2·2CH2Cl2 (4), the crystal structure of which is described. Complex 4 was also formed by the reaction of 2 with iodosylbenzene.