Three-Coordinate Copper(I) Amido and Aminyl Radical Complexes

Abstract

A three-coordinate Cu−NR₂ system (R = p-tolyl) supported by the anionic bis(phosphino)borate ligand [Ph₂B(CH₂P^tBu₂)₂]⁻ has been isolated and structurally characterized in both its anionic Cu^I and neutral (formally) Cu^II oxidation states. A large rate constant for the self-exchange electron-transfer reaction (k_S ≥ 10⁷ M⁻¹ s⁻¹) makes this system a functional model for the type-1 active sites in blue copper proteins. Multiedge X-ray absorption spectroscopy, multifrequency electron paramagnetic resonance, and density functional theory analyses collectively indicate that the oxidized form is best regarded as a Cu^I−aminyl radical complex rather than a Cu^II−amido species, with about 70% localization of the unpaired electron on the NR₂ unit. Hydrogen-atom transfer and C−C coupling reactions are presented as examples of chemical reactivity manifested by this unusual electronic structure.