C-C and C-O Coupling Reactions of Terminal Alkynes by a Water Soluble Organoiridium Electron-transfer Mediator in Thin Layer of Water on Gold Electrode

Abstract

An electrochemical reduction process is described for the rapid and efficient conversion of terminal alkynes into useful products. Terminal alkynes (HC≡CR; R = C 6 H 5 , p -C 6 H 4 CH 3 , CH 2 C 6 H 5 , C 6 H 9 ) were hydrated and dimerized by cathodic reduction of catalytic amount (5 %) of [Cp * Ir(NCMe) 2 (PAr 3 )](OTf) 2 , 1 , ( E pc = −620 mV vs Ag/AgCl) through an aqueous/nonaqueous interface. Thin aqueous layer containing water-soluble compound 1 was formed on gold electrode. The cathodic reduction current height of 1 increases as increasing the concentration of terminal alkynes. The electrolysis of 1 while contacting with terminal alkynes containing organic solvent produced ketones, aldehydes and dimerized enyne products from terminal alkyne/water reaction systems. A new micro-scale electrocatalysis technique is depicted.