Nickel, Palladium, and Platinum Complexes of η⁵-Cyclopentadienide C₆₀R₅ Ligands. Kinetic and Thermodynamic Stabilization Effects of the C₆₀Ph₅ Ligand

The nickel−, palladium−, and platinum−RFCp complexes Ni(η⁵-RFCp)(η³-allylic) (3b, RFCp = C₆₀R₅, R = Me, allylic = methallyl; 4a, R = Ph, allylic = allyl; 4b, R = Ph, allylic = methallyl), Pd(η⁵-RFCp)(η³-allylic) (7a, R = Me, allylic = allyl; 7b, R = Me, allylic = methallyl; 7c, R = Me, allylic = crotyl; 8a, R = Ph, allylic = allyl; 8b, R = Ph, allylic = methallyl; 8c, R = Ph, allylic = crotyl), and Pt(η⁵-RFCp)(η³-methallyl) (9, R = Me; 10, R = Ph), were synthesized by transmetalation between K(RFCp) (R = Me, Ph) and [Ni(allylic)Br]₂, [Pd(allylic)Cl]₂, or [Pt(methallyl)Cl]₂ in THF at 25 °C for 10 min. The nickel−PhFCp complexes 4a,b are unusually more stable toward molecular oxygen than the corresponding simple nickel cyclopentadienides and survive in air for many hours at elevated temperature. The crystal structures and the electrochemical properties of the palladium complexes suggest that the unusual stability of the PhFCp complexes is due to the kinetic stabilization effect of the five Ph groups surrounding the metal atom and the thermodynamic stabilization effect of the electron-withdrawing fullerene moiety, hence suggesting new opportunities for the synthesis of otherwise unstable organometallic compounds.