Electrochemical Reduction of Dihalo-2,2[sup ʹ]-bithiophenes at Carbon Cathodes in Dimethylformamide

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Abstract
Cyclic voltammetry and controlled-potential electrolysis have been employed to investigate the electrochemical reduction of 3,3′3,3′ -dibromo-, 5,5′5,5′ -dibromo-, and 5,5′5,5′ -dichloro- 2,2′2,2′ -bithiophenes at carbon cathodes in dimethylformamide containing tetramethylammonium perchlorate. Reduction of 5,5′5,5′ -dibromo- and 5,5′5,5′ -dichloro- 2,2′2,2′ -bithiophene gives rise to three cyclic voltammetric waves that correspond to the reductive cleavage of the carbon-bromine bonds and to the reduction of 2,2′2,2′ -bithiophene. Cyclic voltammograms for the reduction of 3,3′3,3′ -dibromo- 2,2′2,2′ -bithiophene exhibit two cathodic waves attributed to the scission of the carbon-bromine bonds and to reduction of 2,2′2,2′ -bithiophene. Bulk electrolyses of dihalo- 2,2′2,2′ -bithiophene at potentials for different stages of reduction lead to products that are consistent with expectations based on cyclic voltammetry. Controlled potential catalytic reductions of 3,3′3,3′ -dibromo-, 5,5′5,5′ -dibromo-, and 5,5′5,5′ -dichloro- 2,2′2,2′ -bithiophene by electrogenerated nickel(I) salen afford the corresponding monohalo- 2,2′2,2′ -bithiophene in high yield (74-83%) through a one-electron process. © 2002 The Electrochemical Society. All rights reserved.

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