Stabilization of copper dioxygen compounds: Design, synthesis, and characterization

Oxygenation in acetonitrile of the copper(I) complex of the rigid tetradent ate, substituted bispidine ligand L-1 with a diamine-bis-pyridinyl donor se t (L-1 = methyl 2,4-bis(2-pyridinyl)-3,7-diazabicyclo-[3.3.1]-nonane-9-di-o l-1.5-dicarboxylate) produces an end-on (mu-peroxo)dicopper(II) compound th at is stable in solution up to 250 K. The spectroscopic characterization of this species (UV/visible and Raman spectroscopy) and an X-ray structural a nalysis of the corresponding mononuclear copper(II) compound [Cu(L-1)Cl](+) indicate that the deep purple oxygenation product has two distorted square pyramidal copper(II) chromophores linked by a mu-peroxo bridge. Molecular mechanics calculations were used to interpret the relative stability of the copper dioxygen product [{Cu(L-1)}(2)O-2](2+) and to design the nucleating ligand L-2 bsed on two L1 binding sites, linked an ethyl bridge. The corre sponding deep purple copper dioxygen product [Cu-2(L-2)(O-2)](2+) has spect roscopic characteristics (UV/visible and Raman spectra) that are similar bu t not identical to those of [{Cu(L-1)}(2)O-2](2-); this (mu-peroxo)dicopper (II) compound is stable at ambient temperature (t(1/2)(298 K) = 50 min).