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) (AlAuPBu3)-Bu-t (where NON is the chelating tridentate ligand 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) thene) that features a strongly polarized bond, Aud(delta-)-Al delta+. This is synthesized by reaction of the potassium aluminyl compound [K{Al(NON)}](2) with (Bu3PAuI)-Bu-t. 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) (AuPBu3)-Bu-t (X = (NPr)-Pr-i, 4; X = O, 5).