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

A three-coordinate Cu-NR2 system (R = p-tolyl) supported by the anionic bis(phosphino)borate ligand [Ph2B((CH2PBu2)-Bu-t)(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) >= 10(7) 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.