Copper-dioxygen reactivity using dinucleating ligands with activated methylene or ketone function

Copper(I)-dioxygen reactivity studies utilizing new binucleating ligands are described. When catalytic quantities of either CuI or Cu II salts were introduced to LH2, which is a dinucleating ligand with two tridentate donors connected via a methylene group at a bis(2-pyridyl)methane junction, dioxygen addition caused complete oxygenation to give bis(2-pyridyl)ketone product L=O. Isolated dicopper(I) complex [Cu I2(LH2)]2+ (1) also reacted with excess O2 to give L=O. Additional observations were consistent with a mechanism that does not involve "oxygen-activation" in this process. Ketone hydration and gem-diol(ate) copper(II)-coordination occurred by addition of copper(II)-perchlorate to L=O, giving [CuII2{L(OH) (O-)}Cu2II(-OClO3)] 2+ (4), with a bridging alkoxide moiety (X-ray). Oxygenation of [CuI2(L=O)(CH3CN)2]2+ (2) (2/O2 = 0.5, i.e., Cu/O2 = 4:1 manometry), gave [Cu II2{L(O-)2}(-OClO 3)]+ (5), where both oxygen atoms of the doubly deprotonated gem-diolate bind separate copper(II) ions; mass spectrometric data showed that one of the two oxygen atoms of the gem-diolate L(O-) 2 came from O2. An oxo-dicopper(II) species is suggested as an important intermediate, which is supported by the observation that reaction of 2 with NO or iodosylbenzene also produced 5 in high yields. Complexes 4 and 5 are acid-base conjugate pairs and can be readily interconverted using Et3N or HClO4(aq) reagents. © 2007 The Chemical Society of Japan.