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

The cationic gold π-allene complex {[P(<i>t</i>-Bu)<sub>2</sub><i>o</i>-biphenyl]Au[η<sup>2</sup>-H<sub>2</sub>CCC(CH<sub>3</sub>)<sub>2</sub>]}<sup>+</sup>SbF<sub>6</sub><sup>−</sup> was isolated in 98% yield from reaction of 3-methyl-1,2-butadiene with a mixture of [P(<i>t</i>-Bu)<sub>2</sub><i>o</i>-biphenyl]AuCl and AgSbF<sub>6</sub> 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 π-face exchange of the allene ligand via an η<sup>1</sup>-C2 allene intermediate or transition state.