A nucleophilic gold complex

Solid-state auride salts featuring the negatively charged Au^- ion are known to be stable in the presence of alkali metal counterions. While such electron-rich species might be expected to be nucleophilic (in the same manner as I^-, for example), their instability in solution means that this has not been verified experimentally. Here we report a two-coordinate gold complex (NON)AlAuP^tBu₃ (where NON is the chelating tridentate ligand 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) that features a strongly polarized bond, Au^δ--Al^δ+. This is synthesized by reaction of the potassium aluminyl compound [K{Al(NON)}]₂ with ^tBu₃PAuI. Computational studies of the complex, including quantum theory of atoms in molecules charge analysis, imply a charge at gold (-0.82) that is in line with the relative electronegativities of the two metals (Au: 2.54; Al: 1.61 on the Pauling scale). Consistently, the complex is found to act as a nucleophilic source of gold, reacting with diisopropylcarbodiimide and CO₂ to give the Au-C bonded insertion products (NON)Al(X₂C)AuP^tBu₃ (X = NⁱPr, 4; X = O, 5).