Oxygenation of copper(I) with tetradentate tripodal ligands (L) comprised of a tris(aminoethyl)amine (tren) skeleton having sterically bulky substituent(s) on the terminal nitrogens has been investigated, whereAll the copper(I) complexes reacted with dioxygen at low temperatures to produce superoxocopper(II) and/ or trans-("-1,2-peroxo)-dicopper(II) complexes depending on the steric bulkiness of the terminal nitrogens and the reaction conditions. The reaction of a copper( þ ($0:24 mM) and higher dioxygen concentration (P(O 2 ) = $1 atm), the superoxo species is predominantly formed, whereas at a higher concentration of [Cu(L Me,Bn )] þ ($1 mM) and lower dioxygen concentration (P(O 2 ) = $0:02 atm) the formation of the peroxo species is observed.

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