Formation of Redox-Active, Two-Component Films by Electrochemical Reduction of C 60 and Transition Metal Complexes Alan L. Balch,* David A. Costa, and Krzysztof Winkler Contribution from the Department of Chemistry, UniVersity of California, DaVis, California 95616, and the Institute of Chemistry, UniVersity of Bialystok, Bialystok, Poland ReceiVed February 18, 1998 Abstract: Electrochemical reduction of C 60 in 4:1 toluene/acetonitrile solution in the presence of (PhCN) 2 - PdCl 2 , Ir(CO) 2 Cl(p-toluidine), or (CF 3 CO 2 ) 4 Rh 2 produces three different, redox-active, black films that coat the electrode. These films are insoluble in common organic solvents and adhere strongly to the electrode surface. Film formation has been monitored by multiscan cyclic voltammetry, which gives information about the requirements for film growth. The three different films (on the original electrodes) can be transferred to a solution of acetonitrile that contains only the supporting electrolyte, tetra(n-butyl)ammonium perchlorate, where the films retain their redox activity. Each film displays a significant decrease in resistivity (i.e. a window of conductivity) in the potential region in which it is grown and in which it displays redox activity. The films have been examined by scanning electron microscopy, which shows variations in the nature of the three films’ morphologies with the film formed from (PhCN) 2 PdCl 2 displaying the greatest uniformity and smoothest surface. Analysis of the films by infrared spectroscopy and laser desorption mass spectrometry reveals that intact C 60 units are present within each film. Treatment of the palladium/C 60 film with triphenylphosphine results in film dissolution and the formation of the previously characterized complex, (η 2 -C 60 )Pd(PPh 3 ) 2 . The rhodium/ C 60 film dissolves in pyridine and 19 F{ 1 H} NMR spectroscopy reveals that (CF 3 CO 2 ) 4 Rh 2 is extracted intact from the film. The structure of the films is discussed in terms of covalent bonding between the fullerenes and the metal atoms or complexes within the film. Introduction Although the process of fullerene polymerization has proven to be challenging, significant progress has also been made in the polymerization of fullerenes through high pressure, 1 pho- tochemical, 2 and chemical 3 methods. Fullerenes have also been chemically modified to facilitate the formation of charm bracelet polymers. 4 Recently, this laboratory has shown that redox active, fullerene-based films, which are believed to be polymers based on their insolubility in common solvents, can be formed by the electrochemical reduction of either the fullerene epoxide, C 60 O, 5,6 or of a mixture of C 60 and dioxygen 7 in toluene/ acetonitrile solution. These films appear to be related to the conducting polymers such as polyaniline, polypyrrole, and polythiophene, that are generally obtained by oxidation of corresponding monomers. 8 The film produced by electrore- duction of C 60 O has been shown to have the ability to store up to eight electrons per fullerene unit, and thus has potential as a component in an energy storage battery. 9 Here we describe a new electrochemical approach to the formation of fullerene- based polymers through a two-component polymerization that utilizes the formation of covalent bonds between transition metal complexes and fullerenes to form the polymeric network. The electrochemistry of C 60 , both in solution and as thin films on electrodes, has received considerable study. 10 Six reversible, one-electron reduction waves are seen in solution. These processes involve filling of the triply degenerate LUMO of C 60 . Additionally, a reversible, one-electron oxidation is observed at relatively high potential. Our initial work began with the development of an electro- chemical procedure for the formation of the previously known polymer, C 60 Pd n , where n can range from 1 to 7. 11,12 This black material has been prepared in amorphous form by the chemical reaction between C 60 and a palladium(0) complex such as tris- (dibenzylideneacetone)dipalladium(0). The C 60 Pd n polymer, which is a heterogeneous catalyst for hydrogenation reactions, 13 is insoluble in common organic solvents but dissolves in the (1) Rao, A. M.; Zhou, P.; Wang, K.-A.; Hager, G. T.; Holden, J. M.; Wang, Y.; Lee, W.-T.; Bi, X.-X.; Eklund, P. C.; Cornett, D. S.; Duncan, M. A.; Amster, I. J. Science 1993, 259, 955. (2) Fischer, J. E. Science 1994, 264, 1548. Iwasa, Y.; Arima, T.; Fleming, R. M.; Siegrist, T.; Zhou, O.; Haddon, R. C.; Rothberg, L. J.; Lyons, K. B.; Carter, H. L., Jr.; Hebard, A. F.; Tycko, R.; Dabbagh, G.; Krajewski, J. J.; Thomas, G. A.; Yagi, T. Science 1994, 264, 1570. 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