A Molecular Boroauride: A Donor-Acceptor Complex of Anionic Gold

Gold is unique among the transition metals in that it is stable as an isolated anion (auride). Despite this fact, the coordination chemistry of anionic gold is virtually nonexistent, and this unique oxidation state is not readily exploited in conventional solution chemistry owing to its high reactivity. Through the use of a new molecular scaffold based on diboraanthracene (B2P2, 1), we have overcome these issues by avoiding the intermediacy of zerovalent gold and stabilizing the highly reduced gold anion through acceptor interactions. We have thus synthesized a molecular boroauride [(B2P2)Au]− ([2]−) and showed its reversible conversion between Au−I and AuI states. Through a combination of spectroscopic and computational studies, we show the neutral state to be a AuI complex with a ligand radical anion. Bonding analyses (NBO and QTAIM) and the isolobal relationship between gold and hydrogen provide support for the description of [2]− as a boroauride complex.