ELECTROCHEMICAL STUDIES ON METAL DERIVATIVES OF BUCKMINSTERFULLERENE (C-60)

The electrochemical properties of the complexes (Ph3P)2Pt(eta-2-C60), (Et3P)2M(eta-2-C60), [(Et3P)2M]6C60 (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(eta-2-C60) and (Et3P)2 M(eta-2-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(eta-2-C60)2- > (Et3P)2Pt(eta-2-C60)2-), the metal (Ni > Pd > Pt), and the extent of reduction ((Et3P)2PtC603- > (Et3P)2PtC602- > (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(eta-2-CH2=CHCO2CH3) (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.