A DICOPPER(I) COMPLEX AND ITS OXYGENATION CHEMISTRY USING A DINUCLEATING LIGAND WITH A PENDANT ALKENE GROUP

A dicopper(I) complex with new dinucleating ligand has been synthesize d and structurally characterized and its reactivity with dioxygen inve stigated. The N3OR1 ligand contains two tridentate PY2 (PY2 - bis[2-(2 -pyridyl)ethyl] amine) chelating groups with connecting group possessi ng an appended cinnamoyl group. An X-ray structure of [Cu2(N3OR1)](PF6 )2 (1) reveals unsymmetrical coordination of Cu(I) ions; one metal ion is three-coordinate, exhibiting typical ligation to the PY2 unit, whi le the other is tetracoordinate, also binding the cinnamoyl alkene gro up. H-1-NMR spectroscopy confirms alkene coordination in solution, whi le temperature-dependent studies reveal a dynamic behavior indicating the alkene switches ligation between cuprous ions. Below approximately -70-degrees-C, binding of O2 (Cu/O2 = 2:1, manometry) to yellow comple x 1 gives a stable adduct [Cu2(N3OR1)(O2)] (PF6)2 (2), characterized b y strong charge-transfer absorptions, lambda(max) = 354 nm, epsilon = 26 500 M-1 cm-1. By analogy to other complexes, 2 is best described as a peroxo-dicopper(II) species, most likely with a bent side-on mu-eta 2:eta2-peroxo bridging ligand, also consistent with the observed diama gnetism (i.e., near normal H-1-NMR spectrum at -90-degrees-C and EPR s ilent). The binding of O2 to 1 is reversible, as shown by the ability to cycle between 1 and 2, via removal of dioxygen from 2 by applicatio n of a vacuum while heating. At room temperature, reaction of 1 with O 2 gives a green dicopper(II) complex, suggested to be an oxo-bridged s pecies [Cu2(N3OR1)(O)](PF6)2-CH2Cl2 (3), typical of reactions involvin g 4 Cu(I)/O2 chemistry. The N3OR1 ligand remains intact under these co nditions, indicating that no oxidation or other reaction has occurred on the cinnamoyl group, in spite of its proximity to the Cu2-O2 which formed during the reaction. Possible reasons for this, and the relatio nship of dioxygen complex 2 to other protein or synthetically derived copper-dioxygen complexes is discussed.