Propargyl radicals are known to dimerize at diffusion-controlled rates with C-C bonds being formed at propargyl and allenic termini. Not only does the complexation of the triple bond allow for precluding an acetylene-allene rearrangement, but it also provides a mechanistic tool for altering the intrinsic nature of propargyl radicals, i. e. from transient to persistent. A wide range of substituents was incorporated alpha and gamma to a metal core, and dimerization reactions were studied with zinc, or cobaltocene, acting as reducing agents. In contrast to organic radicals, tertiary Co2(CO)6-complexed propargyl radicals were found to be persistent in nature, while their secondary counterparts can dimerize with alpha substituents as bulky as a naphthyl group. Computation methods (semiempirical, DFT) were used to quantitatively assess the steric threshold for transient-to-persistent conversion, while the multiple bonds were exploited for relieving a steric strain and projecting an original reaction site gamma to a metal core.

From transient to persistent propargyl radicals: Exploiting a steric factor

248th National Meeting (2014)

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