Copper(i) complexes based on ligand systems with two different binding sites: synthesis, structures and reaction with O2

Abstract

The synthesis of the ligand systems L¹ and L² with two different N₃-binding sites linked through a dibenzofuran spacer and their coordination properties towards a variety of Cu^I precursors are reported. The reaction of L¹ with copper halides leads to the formation of a bimetallic species [(L¹)(Cu^ICl)₂] (1), and metallodimers [((L¹)(Cu^IX)₂)₂(μ-(Cu^I₂)(μ-X)₂)] (2: X = Br, 3: X = I) in which two dicopper complexes are bridged by a (μ-(Cu^I₂)(μ-X)₂)-moiety whereas L² reacts with copper chloride to afford {[Cu^I₂(L²)Cl₂]}_n (8). Furthermore, starting from L¹ in combination with copper(I) salts of weakly coordinating anions the dicopper complexes [(L¹)(Cu^I(NCCH₃))₂](BF₄)₂ (4), [(L¹)(Cu^I(NCCH₃))(Cu(Y))](Y) (5: Y = OTf, 6: Y = ClO₄) and [(L¹)(Cu^I₂(dppe))](PF₆)₂ (7) were isolated, and employing L², the complexes [(L²)(Cu^I(NCCH₃))₂](Z)₂ (9: Z = PF₆, 10: Z = OTf) and [(L²)(Cu^I₂(dppe))](PF₆)₂ (11) were obtained. Complexes 4–6 as well as 9 and 10 react rapidly with O₂ to form metastable O₂ adducts in acetone at −90 °C, where O₂ is bound between the two copper centers within one dicopper molecule, as evidenced by UV/Vis spectroscopy, kinetic investigations, Raman spectroscopy and studies with ligands containing the isolated donor sites. The reactivity of the O₂ adducts towards selected substrates was also investigated, showing their ability to act as electrophiles as well as nucleophiles.