Electrochemical studies on metal derivatives of buckminsterfullerene (C60)

Article abstract of DOI:10.1021/ja00046a029

The electrochemical properties of the complexes (Ph₃P)₂Pt(η²-C₆₀), (Et₃P)₂M(η²-C₆₀), [(Et₃P)₂M]C₆₀ (M = Ni, Pd, Pt; Et - ethyl, Ph - phenyl), and [(Et₃P)₂Pt]_nC₆₀ (n = 2-4) have been investigated. In the case of the monosubstituted complexes (Ph₃P)₂Pt(η²-C₆₀) and (Et₃P)₂M(η²-C₆₀), three to four sequential one-electron reduction waves are observed shifted to more negative potentials relative to C₆₀. Reduction is accompanied by loss of the metal fragment (R₃P)₂M. The rate of metal dissociation upon reduction is dependent on the identity of the phosphine ligand ((Ph₃P)₂Pt(η²-C₆₀)^2- > (Et₃P)₂Pt(η²-C₆₀)^2-), the metal (Ni > Pd > Pt), and the extent of reduction ((Et₃P)₂PtC₆₀^3- > (Et₃P)₂PtC₆₀^2- > (Et₃P)₂PtC₆₀^-). The cyclic voltammograms have been simulated to obtain kinetic and thermodynamic information regarding these processes. The reduction events in the metal complexes are C₆₀-centered, whereas the irreversible oxidation waves observed for these complexes are proposed to be metal-centered from comparison with the model complexes (Et₃P)₂M(η²-CH₂=CHCO ₂CH₃) (M = Ni, Pd, Pt). The results lead to the conclusion that there is negligible extension of d-orbital backbonding density beyond the carbon-carbon double bond where the metal is attached. Coordination of one of these metals to C₆₀ is proposed to lower the electron affinity of the carbon cluster by effectively removing one of the C₆₀ carbon-carbon double bonds from conjugation and inductively adding electron density to the a bond framework. Addition of more metals continues to lower the electron affinity of the C₆₀ core, with the reversible potentials for [(Et₃P)₂Pt]_nC₆₀ shifting 0.36 V in the negative direction with each metal added for n = 0-4.