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• 137516-01-9 tris(2-benzylaminoethyl)amine 

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Dioxygen Reactivity of Copper(I) Complexes with Tetradentate Tripodal Ligands Having Aliphatic Nitrogen Donors: Synthesis, Structures, and Properties of Peroxo and Superoxo Complexes

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, where L = tris(N-benzylaminoethyl)amine (LH,Bn), tris(N-benzyl-N-methylaminoethyl)amine (LMe,Bn), or tris(N,N-dimethylaminoethyl)amine (LMe,Me). All the copper(I) complexes reacted with dioxygen at low temperatures to produce superoxocopper(II) and/ or trans-(μ-1,2-peroxo)-dicopper(II) complexes depending on the steric bulkiness of the terminal nitrogens and the reaction conditions. The reaction of a copper(I) complex [Cu(LH,Bn)] + at -90 °C in acetone resulted in the formation of a superoxo complex [Cu(LH,Bn)(O2)]+ as a less stable species and a peroxo complex [{Cu(LH,Bn)}2(O2)] 2+ as a stable species. The structures of [Cu(L H,Bn)]ClO4 and [{Cu(LH,Bn)}2(O 2)](BPh4)2·8(CH3) 2CO were determined by X-ray crystallography. [{Cu(L H,Bn)}2(O2)]2+ has a trans-(μ -1,2-peroxo)-dicopper(II) core with a trigonal bipyramidal structure. The O-O bond distance is 1.450(5) A with an intermetallic Cu...Cu separation of 4.476(2) A. The resonance Raman spectrum of [{Cu(L H,Bn)}2(O2)]2+ measured at -90 °C in acetone-d6 showed a broad ν(O-O) band at 837-834 cm-1 (788 cm-1 for an 18O labeled sample) and two ν(Cu-O) bands at 556 and 539 cm-1, suggesting the presence of two peroxo species in solution. [Cu(LMe,Bn)]+ also produced both superoxo and trans-μ-1,2-peroxo species, [Cu(LMe,Bn)(O 2)]+ and [{Cu(LMe,Bn)}2(O 2)]2+. At a lower concentration of [Cu(L Me,Bn)]+ (～0.24 mM) and higher dioxygen concentration (P(O2) = ～1 atm), the superoxo species is predominantly formed, whereas at a higher concentration of [Cu(LMe,Bn)]+ (～1 mM) and lower dioxygen concentration (P(O2) = ～0.02 atm) the formation of the peroxo species is observed. The resonance Raman spectrum of [Cu(LMe,Bn)(O2)]+ (～1 mM) in acetone-d6 at ～-95 °C exhibited a μ(O-O) band at 1120 cm-1 (1059 cm-1 for an 18O labeled sample) and that of [{Cu(LMe,Bn)}2(O2)]2+ (～3 mM) in acetone-d6 at ～-90 °C showed two ν(O-O) bands at 812 and 797 cm-1 (767 and 753 cm-1 for an 180 labeled sample), respectively. A similar observation was also made for [{Cu(LMe,Me)}2(O2)]2+. Relationships between the energies of the LMCT and d-d transitions and those of the ν(O-O) and ν(Cu-O) stretching vibrations and the steric constraints in the Cu(II)-(O22-)-Cu(II) core are discussed.