Dioxygen Reactivity of Bioinspired Copper(I) and Copper(I)/Manganese(II)-Porphyrin Systems

Transition metal-dioxygen (O2) interactions are of great importance in biological and chemical transformations involving dioxygen binding, activation, or reduction. In this work, the independent O2 reactivity of a series of bioinspired copper(I) complexes with varying ligand electronic environments, as well as the cooperative O2 reactivity of a copper(I)/manganese(II)-porphyrin assembly, were studied via variable temperature absorption (VT UV-vis-NIR), nuclear magnetic resonance (NMR), and infrared (IR) spectroscopies, along with X-ray crystallography, cyclic voltammetry (CV), and electrospray ionization mass spectrometry (ESI-MS). Our spectroscopic studies confirmed that the copper(I) complexes reversibly react with O2 to form the corresponding 1:1 copper-O2 (i.e., end-on superoxo) intermediates which can further react reversibly with second equivalents of copper(I) complexes to form the related dinuclear 2:1 copper-O2 (i.e., trans-peroxo) adducts. Small but significant variations in the Cu/O2 adducts’ spectroscopic features suggest that electronic variation in the copper chelates directly affects the electronic properties of the copper-O2 cores. Furthermore, the bioinspired copper(I) complex [(tmpa)Cu(I)(MeCN)]+ (TMPA: tris[(2-pyridyl)methyl]amine) was observed to “trigger” the O2 reactivity of a manganese(II) porphyrin which displays no independent O2 chemistry at ambient conditions: In the presence of one or two equivalents of the O2-active copper center, the O2-inert manganese center was “triggered” to cooperatively activate O2 and perform one or two electron transfers, generating the first examples of such Mn(III)/Cu(II)/O2 or Mn(IV)/Cu(II)/O2 species, respectively. The observed cooperative O2 chemistry was not possible for either metal center independently