| SYNTHESIS |
Cobalt-propargyl radical-radical dimerization Cobalt-complexed propargyl alcohols have been shown to form isolable cationic species that, in turn, can be induced to form radicals that dimerize with up to 98% diastereoselectivity [Org. Lett., 5, 3395 (2003)]. The work provides a new example of intermolecular coupling of ligand-based organometallic radicals and is reportedly the first case of spontaneous radical formation in a cobalt-alkyne system. Chemistry professor Gagik G. Melikyan and coworkers at California State University, Northridge, reacted propargyl alcohols with HBF4 to form salts that are stable at low temperature. When a salt is dissolved in dichloromethane and warmed to room temperature, a radical forms at the original alcohol substituent site of the compound, and radical-radical coupling leads to the dimer (shown; M = Co2(CO)6, R = H or OCH3). The dimers also can be prepared without isolating the intermediate by using triflic anhydride in place of HBF4. The results suggest that cobalt-complexed propargyl radicals should be synthetically useful to stereoselectively form "larger molecular assemblies of biological relevance," Melikyan tells C&EN. |
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