14-Membered Macrocyclic β-Diiminato Gold(II) - A New Member for the Gold(II) Complex Family?

Abstract

The chemistry of molecular gold compounds is dominated by the oxidation states +I and +III. For the intermediate oxidation state +II with 5d⁹ electron configuration, dimerization or disproportionation of the gold(II) radicals is favored, so that only a few mononuclear gold(II) complexes have been isolated to date. The present study addresses the one-electron reduction of the macrocyclic gold(III) complex [Au^IIIL]⁺ of the innocent β-diiminato ligand L^2- with a 14-membered macrocycle (L^2-=5,7,12,14-tetramethyl-1,4,8,11-tetraazacyclotetradeca-5,7,12,14-tetraenato). Electrochemistry, spectroelectrochemistry and chemical reduction of [Au^IIIL]⁺ monitored by UV/Vis, NMR and EPR spectroscopy together with density functional theory calculations reveal disproportionation of the initially generated but elusive gold(II) complex Au^IIL and provide guidelines for prospective stable mononuclear tetraazamacrocyclic gold(II) complexes.

Keywords: disproportionation; gold; macrocycle; redox chemistry.