Probing the nature of gold–carbon bonding in gold–alkynyl complexes

Homogeneous catalysis by gold involves organogold complexes as precatalysts and reaction intermediates. Fundamental knowledge of the gold–carbon bonding is critical to understanding the catalytic mechanisms. However, limited spectroscopic information is available about organogolds that are relevant to gold catalysts. Here we report an investigation of the gold–carbon bonding in gold(I)–alkynyl complexes using photoelectron spectroscopy and theoretical calculations. We find that the gold–carbon bond in the ClAu–CCH(−) complex represents one of the strongest gold–ligand bonds—even stronger than the known gold–carbon multiple bonds, revealing an inverse correlation between bond strength and bond order. The gold–carbon bond in LAuCCH(−) is found to depend on the ancillary ligands and becomes stronger for more electronegative ligands. The strong gold–carbon bond underlies the catalytic aptness of gold complexes for the facile formation of terminal alkynyl–gold intermediates and activation of the carbon–carbon triple bond.