Reactivity of Copper Complexes with Tripodal Tetradentate Ligands based on Camphoric Acid towards Dioxygen

Abstract

The reaction of dioxygen with copper(I) complexes containing camphor-derived ligands was investigated. Stopped-flow measurements revealed the formation of bis(μ-oxido) copper complexes at low temperatures. However, these intermediates were not stable enough to be isolated and decomposed quickly. Sterically more demanding alkyl groups slowed the formation of the bis(μ-oxido) copper complexes. A kinetic analysis was performed and showed - in line with previous reports - that the rate-determining step could be assigned to forming a mononuclear superoxido copper complex. For one of the reactions investigated, a product could be structurally characterized and turned out to be a copper(II) complex with an additional hydroxide as a ligand (most likely caused by a C−H abstraction from the solvent acetone). One of the complexes oxidized thioanisole to the corresponding sulfoxide (conversion of 34 % according to GC-MS) with no byproducts. Chiral GC gave an enantiomeric excess of 14 %.