Anodic oxidation induced [2+2] carbon-carbon coupling reactions of terminal alkenes using organo-Re(II) electron transfer mediator

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May, Joshua Paul
Chong, Daesung
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Thesis (M.S.)
Department of Chemistry
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The radical cation, [ReCp(CO)3]+ (1+, Cp = η5-C5H5) has been utilized to initiate radical-based intermolecular carbon-carbon coupling reactions of unsubstituted terminal alkenes. Characterization of the 1/1+ couple was recently made possible by the application of the weakly coordinating anion [B(C6F5)4-] of the supporting electrolyte. The very nature of the 1/1+ couple (E1/2 = 1.16 V vs. Fc0/+) makes 1+ a powerful one-electron oxidizing agent. The in situ anodic generation of 1+ by electrolysis at 1.3 V initiates coupling reactions between excessively added linear alkenes with individual E1/2 values exceeding 1.8 V. The exceptional catalytic oxidation process between 1+ and each terminal alkene is theorized to occur by means of an electron-transfer mechanism. Carbon-carbon coupling reactions for 1-octene, 1,7-octadiene, and 1-hexene have been conducted, as well as focused experiments with increased concentrations of 1-octene to a 1:50 (1:1-octene) mole ratio was employed. Primary products of these reactions were unique to each alkene and 1-octene produced cyclobutyl-derivative major products. Catalytic bulk oxidation of 1 in each case was exhausted in < 25 min., following the passage of 0.01 - 0.3 F/mol of alkenes. Products from these coupling reactions were obtained in 60-73% yields and identified by GC-MS, 1H-NMR, 13C-NMR, DEPT, and HMQC NMR spectroscopic data analyses. The mechanisms of these reactions will be discussed. Presented is an efficient synthetic tool of [2+2] carbon-carbon coupling reactions under mild conditions and the pertinent ramifications therein.