Ligand exchange reactions in the formation of diphosphine-protected gold clusters

Ligand exchange reactions important in the formation of L-3- and L-5-protected gold clusters (L-3 = 1,3-bis(diphenylphosphino)propane; L-5 = 1,5-bis(diphenylphosphino)pentane) are investigated at the molecular level. We establish that molecular complexes, [Au(PPh3)(x)L-2-x('')](+), in which Au+ is bound to at least one triphenylphosphine ligand (PPh3) act as precursors to cluster formation, while complexes in which Au+ is bound only to the diphosphine ligands do not. Ligand exchange reactions and ion equilibria were studied via electrospray ionization mass spectrometry, and a critical reaction was studied with ab initio molecular dynamics simulations. The displacement of one PPh3 by L-3 on [Au(PPh3)(2)](+) was studied with transition path sampling calculations with Car-Parrinello molecular dynamics simulations. The experiments and simulations are in excellent agreement, and we demonstrate the applicability of these tools to chemical reactions involving ligand exchange.