Copper Chemistry of β-Diketiminate Ligands: Monomer/Dimer Equilibria and a New Class of Bis(μ-oxo)dicopper Compounds

A series of Cu(I) and Cu(II) complexes of a variety of β-diketiminate ligands (L-) with a range of substitution patterns were prepared and characterized by spectroscopic, electrochemical, and, in several cases, X-ray crystallographic methods. Specifically, complexes of the general formula [LCuCl]2 were structurally characterized and their magnetic properties assessed through EPR spectroscopy of solutions and, in one instance, by variable-temperature SQUID magnetization measurements on a powder sample. UV−vis spectra indicated reversible dissociation to 3-coordinate monomers LCuCl in solution at temperatures above −55 °C. The Cu(I) complexes LCu(MeCN) exhibited reversible Cu(I)/Cu(II) redox couples with E1/2 values between +300 and +520 mV versus NHE (cyclic voltammetry, MeCN solutions). These complexes were highly reactive with O2, yielding intermediates that were identified as rare examples of neutral bis(μ-oxo)dicopper complexes on the basis of their EPR silence, diagnostic UV−vis absorption data, and O...