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

Abstract

The reactivity towards dioxygen has been explored for two copper(I) tris(pyrazolyl)-methane complexes, [Cu I((3,5-Me 2-pz) 3CH)(MeCN)](PF 6) 2 ( 1) and [Cu I((3,5-Me 2-4-Br-pz) 3)(MeCN)](PF 6) 2 ( 2). Reversible oxygenation of 1 occurs in CH 2Cl 2 solution at ∼7 °C to yield a 2:1 μ-η 2η 2-peroxo complex [((3,5-Me 2-pz) 3CH) 2Cu 2(μ-O 2)](PF 6) 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 K 21=32 M −2 (at 298 K), Δ H°=−110±5 K J mol −1, Δ S°=−340±18 J K −1 mol −1 (30 min) which have been compared to values for other CuO 2 adducts. Thermal decomposition of this μ-peroxo species yields crystals of a di-μ-hydroxo complex [((3,5-Me 2-pz) 3CH) 2Cu 2(μ-OH) 2](PF 6) 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 CH 2Cl 2 to form [Cu II((3,5-Me 2-4-Br-pz) 3CH) 2](PF 6) 2·2CH 2Cl 2 ( 4), the crystal structure of which is described. Complex 4 was also formed by the reaction of 2 with iodosylbenzene.