Syntheses, X-ray Crystal Structures, and Solution Behavior of Cationic, Two-Coordinate Gold(I) η²-Diene Complexes

A family of cationic gold π-diene complexes of the form {[P(t-Bu)2o-biphenyl]Au(η2-diene)}+SbF6– were isolated in >80% yield from reaction of various dienes with a mixture of [P(t-Bu)2o-biphenyl]AuCl and AgSbF6 and were characterized by spectroscopy and, in four cases, by X-ray crystallography. Solution and solid-state analysis of these complexes established selective binding of gold to the less substituted CC bond of the diene in the case of dienes that possessed differentially substituted CC bonds. 13C NMR analysis and evaluation of the relative binding affinities of substituted dienes point to a bonding model in which the gold–alkene interaction is stabilized via donation of electron density from the uncomplexed CC bond to the complexed CC bond of the diene. Variable-temperature NMR analysis of gold π-diene complexes revealed fluxional behavior consistent with facile (ΔG‡ = 9.6–11.9 kcal mol–1) intramolecular exchange of the complexed and uncomplexed CC bonds of the diene ligand.