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, [Cu-I((3,5-Me-2-pz)(3)CH)(MeCN)](PF6)(2) (1) and [Cu-I((3,5-Me-2-4-Br-pz)(3))(MeCN)](PF6)(2) (2). Reversible oxygenation of 1 occurs in CH2Cl2 solution at similar to7 degreesC to yield a 2:1 mu-eta (2)eta (2-)peroxo complex [((3,5-Me-2-pz)(3)CH)(2)Cu-2(mu -O-2)](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 K-21 = 32 M-2 (at 298 K), DeltaH degrees = -110 +/-5 K J mol(-1), DeltaS degrees = -340 +/- 18 J K-1 mol(-1) (30 min) which have been compared to values for other CuO2 adducts. Thermal decomposition of this mu -peroxo species yields crystals of a di-mu -hydroxo complex [((3,5-Me-2-pz)(3)CH)(2)Cu-2(mu -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 add-act but slowly oxidizes in CH2Cl2 to form [Cu-II((3,5-Me-2-4-Br-pz)(3)CH)(2)](PF6)(2). 2CH(2)Cl(2) (4), the crystal structure of which is described. Complex 4 was also formed by the reaction of 2 with iodosylbenzene. (C) 2001 Elsevier Science B.V. All rights reserved.