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

The cationic gold π-allene complex {[P(t-Bu)₂o-biphenyl]Au[η²-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)₂o-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 π-face exchange of the allene ligand via an η¹-C2 allene intermediate or transition state.