Syntheses, Characterization and Application of Fullerene-Metal Cluster Derivatives

Abstract

Benzyl Isocyanide substituted $C_{60}-triosmium$ complexes, $Os_3(CO)_{9-n}(CNCH_Ph)_n(μ_3-η^2:η^2:η^2-C_{60})$ (n = 2(II-3), 3(II-4), and 4(II-5)), have been prepared by reactions of either $Os_3(CO)_9(μ_-η^2:η^2:η^2-C_{60})$ (II-1) or its lower isocyanide substituted complexes with appropriate amounts of (triphenylphosphino)benzylimine $(PhCH_2N=PPh_3)$. Compounds II-3~II-5 have been characterized by spectroscopic $(IR, MS, ^1H-, ^{13}C-NMR)$ methods, cyclic voltammetry, and X-ray diffraction studies. Single-crystal X-ray diffraction studies reveal that isomer II-3a has two inequivalent equatorial isocyanide ligands as cis,trans-1,2-isomer and isomer II-4a has three equivalent equatorial isocyanide ligands as 1,2,3-isomer with a $C_3$ symmetry. In compound II-5, one benzyl isocyanide is axially coordinated to an osmium atom, whereas the other three benzyl isocyanide ligands are equatorially coordinated to each osmium atom. $^1H$ and $^{13}C-NMR$ data, however, indicate that compound II-3 exists as a mixture of 1,2- (II-3a) and 1,1-isomers (II-3b) in a ratio of 7:1, compound II-4 as a mixture of 1,2,3- (II-4a) and 1,1,2-isomers (II-4b) in a ratio of 1:1, and compound II-5, interestingly, as a single species of 1,1,2,3-isomer in solution. The cyclic voltammetric studies reveal that all the CVs of II-3~II-5 and related $Os_3(CO)_8(CNCH_2Ph)(μ_3-η^2:η^2:η^2-C_{60})$ (II-2) show four reversible redox waves that correspond to one-electron process each with the third and fourth waves overlapped within the chlorobenzene solvent potential window. As more isocyanide ligands are coordinated in II-2~II-5, all the corresponding half-wave potentials are gradually shifted to more negative potentials, reflecting the electron-donor property of the isocyanide ligand. Furthermore, $C_{60}$ -mediated electron delocalization from $C_60$ to the triosmium center takes place in the trianionic species of II-2~II-5 and the two isomers in II-3 and II-4 undergo an equivalent electrochem...