Synthesis and Study of Cationic, Two‐Coordinate Triphenylphosphine– Gold–π Complexes

Cationic, two‐coordinate triphenylphosphine–gold(I)–π complexes of the form [(PPh 3 )Au(π ligand)] + SbF 6 − (π ligand=4‐methylstyrene, 1⋅ SbF 6 ), 2‐methyl‐2‐butene ( 3⋅ SbF 6 ), 3‐hexyne ( 6⋅ SbF 6 ), 1,3‐cyclohexadiene ( 7⋅ SbF 6 ), 3‐methyl‐1,2‐butadiene ( 8⋅ SbF 6 ), and 1,7‐diphenyl‐3,4‐heptadiene ( 10⋅ SbF 6 ) were generated in situ from reaction of [(PPh 3 )AuCl], AgSbF 6 , 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 (Δ G ≠ ≈9 kcal mol −1 in the case of 6⋅ SbF 6 ) 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 [(PPh 3 ) 2 Au] + SbF 6 − ( 2⋅ SbF 6 ).