Decamethylferrocene Redox Chemistry and Gold Nanowire Electrodeposition at Salt Crystal|Electrode|Nonpolar Organic Solvent Contacts John D. Watkins, Christopher E. Hotchen, John M. Mitchels, and Frank Marken* Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, U.K. ABSTRACT: This report describes exploratory experimental findings for electrochemical processes in nonpolar solvents (hexane, toluene, and dichloroethane). Conventional 3 mm diameter glassy-carbon-disk electrodes are used in contact with a crystalline salt electrolyte (ammonium nitrate) immersed in nonpolar solvents. The insoluble salt is employed as a “surface thin film electrolyte”, with humidity causing electrical connection from the working electrode to the SCE counter- reference electrode. The organic solvents are employed without intentionally added electrolyte. Humidity in the nonpolar solvents is shown to be essential for the processes to work. The oxidation of decamethylferrocene is demon- strated as a test organometallic redox system. The electro- chemical reduction of Au(III) in toluene (solubilized with tetraoctylammonium bromide, TOABr) is employed to demonstrate and visualize the reaction zone around salt crystal|working electrode contact points. Gold nanowire bundle formation is observed, presumably due to an ordered interfacial surfactant microphase at salt|electrode contact points. The triple phase boundary nature of these processes is discussed, and future applications are suggested. ■ INTRODUCTION Electrochemical processes for the conversion of organic or organometallic redox systems in nonpolar solvents are important and desirable even in highly nonpolar media such as fluorohydrocarbons, 1 toluene, 2 oils, 3 and heptane. 4 New methods have been developed, for example, on the basis of novel nonpolar solvent soluble and sufficiently dissociated electrolyte salts or ionic liquids, 5,6 on the basis of liquid-liquid triple phase boundary reactor systems 7 where electrolytic conduction is required only in the polar phase, 8,9 and on the basis of particle supported (heterogeneous) electrolyte systems such as pyridinium-substituted polymer beads. 10,11 The last technology allowed substantial currents to be passed and bulk product to be generated with a heterogeneous supporting electrolyte system that is readily recovered by filtration and reused. In the work presented here, a heterogeneous supporting electrolyte system is proposed on the basis of insoluble salt (ammonium nitrate) crystals in contact with the working electrode surface and surrounded by the nonpolar reagent media. Figure 1A shows a schematic drawing with a salt crystal in contact with a glassy-carbon-electrode surface. In a dry nonpolar solvent environment there would be no significant ionic conductivity and therefore electrochemical processes are difficult to observe. However, when the solvent is saturated with water before use (mutual solubilities at 298 K are x 2 =6 × 10 -4 or 4.6 mM for water in hexane, 12 3 × 10 -3 or 28 mM for water in toluene, 13 and 10 × 10 -3 or 130 mM for water in dichloroethane 14 ), the surface of the salt crystals (here ammonium nitrate) will be equilibrated and coated with a thin water layer sufficient for ion conductivity to be achieved. The cation C + , the anion A - , or additional ions such as protons H + are likely to contribute to the charge transport (see Figure 1A) and the overall process. In the vicinity of the contact point of the salt with the electrode surface various types of redox processes become possible, including processes involving redox-active reagents dissolved in the nonpolar solvent. Special Issue: F. Gordon A. Stone Commemorative Issue Received: July 9, 2011 Published: January 10, 2012 Figure 1. Schematic representation of (A) a salt|nonpolar solvent| electrode contact and (B) the electrochemical cell with humidified nonpolar solvent flowing through the salt. Article pubs.acs.org/Organometallics © 2012 American Chemical Society 2616 dx.doi.org/10.1021/om2006112 | Organometallics 2012, 31, 2616-2620