The radical cation, [ReCp(CO)₃]⁺ (1⁺) has been utilized to initiate radical-based, intermolecular, carbon-carbon coupling reactions of, unactivated cyclic olefins. Characterization of the 1/1⁺ couple was recently made possible by the application of the weakly coordinating anion [B(C₆F₅)₄^-] as a supporting electrolyte¹. The very positive nature of the 1/1⁺ couple (E_1/2 value, 1.16 V vs Fc^0/+) makes 1⁺ a powerful one-electron oxidizing agent. The in situ anodic generation of 1⁺ by electrolysis at 1.25 V initiates coupling reactions between excess additions of cyclic olefins with individual E_1/2 values exceeding 1.8 V. The exceptional catalytic oxidation process between 1⁺ and each olefin is theorized to occur by means of an inner-sphere electron-transfer mechanism. Carbon-carbon coupling products for cyclo-pentene, -hexene, -heptene, and -octene have been characterized. Primary products of these reactions were unique to each olefin and entailed either [2+2] and [2+2+2] cycloadditions, or linear dimerizations and trimerizations. Catalytic bulk oxidation of 1 in each case was exhausted in < 1 hour, following the passage of 0.2 – 0.3 F/mol of olefin. Products for these coupling reactions were obtained in 65-79% yields and identified by GC-MS and/or ¹H- and ¹³C-NMR data. The rates and mechanisms of these reactions will be discussed.

(1.) Chong D, Laws DR, Nafady A, et al. J. Am. Chem. Soc. 2008, 130, 2692.