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

A family of cationic gold pi-diene complexes of the form {[P(t-Bu)(2)o-biphenyl]Au(eta(2)-diene)}+SbF6- were isolated in >80% yield from reaction of various dienes with a mixture of [P(t-Bu)(2)o-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. C-13 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 pi-diene complexes revealed fluxional behavior consistent with facile (Delta G(double dagger) = 9.6-11.9 kcal mol(-1)) intramolecular exchange of the complexed and uncomplexed C=C bonds of the diene ligand.