A hydroperoxo-dicopper(II) species, the protonated form of the peroxo-dicopper(II) complex derived from the reaction of O2 with a dicopper(I) compound, is stable at -80 °C in dichloromethane solution and the methods for its generation and its properties are described. This complex, [Cu2(XYL-O-)(OOH)]2+(3), utilizes a phenolic dinucleating ligand possessing two tridentate PY2 units (PY2 = bis[2-(2-pyridyl)ethyl]amine), XYL-OH. A phenoxo-bridged dicopper(I) complex [Cu2-(XYL-O-))]+(1) reacts with O2 to form the previously characterized dioxygen (peroxo) adduct [Cu2(XYL-O-)(O2)]+(2). As shown by a titration followed by UV-vis spectroscopy, one equivalent of H+can be irreversibly added to -80 °C dichloromethane solutions of 2 (isosbestic point observed) to form [Cu2(XYL-O-)(OOH)]2+(3; λmax = 395 nm, ∊ = 8000 M-1 cm-1). Complex 3 can also be generated by reaction of the phenoxo- and hydroxo-bridged dicopper(II) complex [Cu2(XYL-O-)(OH)]2+(4) with hydrogen peroxide, further substantiating its formulation as a peroxidic species. The most convenient method for forming 3 is by the addition of O2(Cu:O2= 2:1) to either [Cu2(XYL-OH)]2+ (5) or [Cu2(XYL-OH)(CH3CN)2]2+ (6d); these dicationic dicopper(I) compounds contain an uncoordinated phenol group. While the dioxygen complex [Cu2(XYL-O-)(O2)]+ (2) reacts with triphenylphosphine (PPh3) liberating O2 quantitatively and providing [Cu2(XYL-O-)(PPh3)2]+ (7), the hydroperoxo complex [Cu2(XYL-O-)(OOH)]2+(3) reacts with PPh3 or sulfides quantitatively to given the monooxygenated substrate (O=PPh3 or RS(O)R) and [Cu2(XYL-O-)(OH)]2+(4), involving the transfer of a single oxygen atom to the substrate. Similar substrate oxygenation reactions can also be carried out by reacting O2 with compounds [Cu2(XYL-OH)(PPh3)2]2+ (6b) or [Cu2-(XYL-OH)(RSR)2]2+(6C,RSR = tetramethylene sulfide). Product analyses (4 also produced quantitatively) show that only 1 mol·equiv of substrate is oxygenated, in accord with the manometric dioxygen uptake (Cu:O2= 2:1); labeling experiments utilizing 18O2show that the product phosphine oxide or sulfoxide contains a single 18O atom. [Cu2(XYL-O-)(OOH)]2+(3) is proposed to contain a μ-1,1-hydroperoxo (-OOH) ligand, based on (i) its structural analogy to [Cu2(XYL-O-)(OH)]2+(4), deduced from an extended X-ray absorption fine structure (EXAFS) analysis, with four N or O donors at 1.99 Å and Cu···Cu = 3.04 Å, and (ii) the chemical and spectroscopic similarities to the recently structurally described acylperoxo complex, [Cu2(XYL-O-)(OOR)]2+ (8, R = M-c1C6H4C(O)-). A crystallographic study of a perchlorate salt of 6b, [Cu2(XYL-OH)(PPh3)2](ClO4)2·(CD3NO2)2 (C74H76D6Cl2Cu2N8O13P2), has been carried out; it crystallizes in the triclinic space group P1 with Z = 1 and a = 10.196 (2)Å, b = 11.715 (2) Å, c = 15.506 (3) Å, α = 94.27 (1)°, β = 90.30 (1)°, and γ = 94.53 (1)°. It contains an uncoordinated phenol group with well-separated (Cu···Cu = 9.944 (2) Å) tetracoordinate Cu(I) ions ligated to the three N atoms of the PY2 unit and a single triphenylphosphine P atom.
ASJC Scopus subject areas
- Colloid and Surface Chemistry