Dioxygen Reactivity of Copper(I)/Manganese(II)-Porphyrin Assemblies: Mechanistic Studies and Cooperative Activation of O 2 .

The oxidation of transition metals such as manganese and copper by dioxygen (O 2 ) is of great interest to chemists and biochemists for fundamental and practical reasons. In this report, the O 2 reactivities of 1:1 and 1:2 mixtures of [(TPP)Mn II ] ( 1 ; TPP: Tetraphenylporphyrin) and [(tmpa)Cu I (MeCN)] + ( 2 ; TMPA: Tris(2-pyridylmethyl)amine) in 2-methyltetrahydrofuran (MeTHF) are described. Variable-temperature (-110 °C to room temperature) absorption spectroscopic measurements support that, at low temperature, oxygenation of the (TPP)Mn/Cu mixtures leads to rapid formation of a cupric superoxo intermediate, [(tmpa)Cu II (O 2 •- )] + ( 3 ), independent of the presence of the manganese porphyrin complex ( 1 ). Complex 3 subsequently reacts with 1 to form a heterobinuclear μ -peroxo species, [(tmpa)Cu II -(O 2 2- )-Mn III (TPP)] + ( 4 ; λ max = 443 nm), which thermally converts to a μ -oxo complex, [(tmpa)Cu II -O-Mn III (TPP)] + ( 5 ; λ max = 434 and 466 nm), confirmed by electrospray ionization mass spectrometry and nuclear magnetic resonance spectroscopy. In the 1:2 (TPP)Mn/Cu mixture, 4 is subsequently attacked by a second equivalent of 3 , giving a bis - μ -peroxo species, i.e., [(tmpa)Cu II -(O 2 2- )-Mn IV (TPP)-(O 2 2- )-Cu II (tmpa)] 2+ ( 7 ; λ max = 420 nm and δ pyrrolic = -44.90 ppm). The final decomposition product of the (TPP)Mn/Cu/O 2 chemistry in MeTHF is [(TPP)Mn III (MeTHF) 2 ] + ( 6 ), whose X-ray structure is also presented and compared to literature analogs.