Synthesis and study of cationic, two-coordinate triphenylphosphine-gold-π complexes.

Cationic, two-coordinate triphenylphosphine-gold(I)-π complexes of the form [(PPh₃)Au(π ligand)]⁺SbF₆⁻ (π ligand=4-methylstyrene, 1∙SbF₆), 2-methyl-2-butene (3∙SbF₆), 3-hexyne (6∙SbF₆), 1,3-cyclohexadiene (7∙SbF₆), 3-methyl-1,2-butadiene (8∙SbF₆), and 1,7-diphenyl-3,4-heptadiene (10∙SbF₆) were generated in situ from reaction of [(PPh₃)AuCl], AgSbF₆, and π ligand at -78 °C and were characterized by low-temperature, multinuclear NMR spectroscopy without isolation. The π ligands of these complexes were both weakly bound and kinetically labile and underwent facile intermolecular exchange with free ligand (ΔG(≠) ≈9 kcal mol(-1) in the case of 6∙SbF₆) and competitive displacement by weak σ donors, such as trifluoromethane sulfonate. Triphenylphosphine-gold(I)-π complexes were thermally unstable and decomposed above -20 °C to form the bis(triphenylphosphine) gold cation [(PPh₃)₂Au]⁺SbF₆⁻ (2∙SbF₆).