Solid-State and Dynamic Solution Behavior of a Cationic, Two-Coordinate Gold(I) π-Allene Complex

The cationic gold pi-allene complex {[P(t-Bu)(2)o-biphenyl]Au[eta(2)-H2C-C-C(CH3)(2)]}(+) SbF6- was isolated in 98% yield from reaction of 3-methyl-1,2-butadiene with a mixture of [P(t-Bu)(2)o-biphenyl]AuCl and AgSbF6 and was characterized by X-ray crystallography and variable-temperature NMR spectroscopy. These studies revealed preferential binding of gold to the less substituted C-C bond of the allene in both the solid state and solution and also revealed fluxional behavior consistent with pi-face exchange of the allene ligand via an eta(1)-C2 allene intermediate or transition state.