Bis(μ-oxo)dicopper(III) complexes of a homologous series of simple peralkylated 1,2-diamines : Steric modulation of structure, stability, and reactivity

We have synthesized and characterized bis(μ-oxo)dicopper(III) dimers 1b−4b (Os) based on a core family of peralkylated trans-(1R,2R)-cyclohexanediamine (CD) ligands, self-assembled from the corresponding [LCu(MeCN)]CF3SO3 species 1a−4a and O2 at 193 K in aprotic media; additional Os based on peralkylated ethylenediamine and tridentate polyazacyclononane ligands were synthesized analogously for comparative purposes (5b−7b and 8b−9b, respectively). Trigonal-planar [LCu(MeCN)]1+ species are proposed as the active O precursors. The 3-coordinate Cu(I) complexes [(LTE)Cu(MeCN)]CF3SO3 (4a) and [(LTB)Cu(MeCN)]CF3SO3 (10a) were structurally characterized; the apparent O2−inertness of 10a correlates with the steric demands of its four benzyl substituents. The rate of O formation, a multistep process that likely proceeds via associative formation of a 1:1 [LCu(O2)]1+ intermediate, exhibits significant dependence upon ligand sterics and solvent:  oxygenation of 4athe slowest-reacting O precursor of the CD seriesis fi...