Cationic Gold Carbonyl Complex on a Phosphine Support

A cationic gold carbonyl complex has been synthesized and characterized using several techniques including X-ray crystallography. [(Mes3P)Au(CO)][SbF6] (Mes = 2,4,6-Me3C6H2) has a linear, two-coordinate gold atom. This compound displays the CO stretching frequency at 2185 cm–1. The 13C NMR signal of the gold-bound 13CO appears as a doublet centered at δ 182.6 (2JC,P = 115 Hz). A computational study shows that the Au–CO bond consists of electrostatic attraction, Au ← CO donation, and significant Au → CO π-back-bonding components. Polarization of the CO bond caused by the electrostatic effect of the cationic gold center is mainly responsible for the large blue shift in the CO stretching frequency.