Homolytic organometallic reactions. Part IV. Homolytic alkylthiyldealkylation of organoboranes

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Abstract
Trialkylboranes react with butane-1-thiol to give dialkylbutylthioboranes, R2BSBun, by a free radical chain mechanism involving bimolecular homolytic substitution by the butylthiyl radical at boron. By competing the trialkylborane with oct-1-ene for the butylthiyl radical relative rates of SH2 attack at boron and addition to the olefin were found. The reversibility of the addition of the thiyl radical to the olefin was taken into account. The occurrence of the SH2 process was also shown by the observation of the e.s.r. spectrum of the displaced alkyl radical when a solution containing a trialkylborane and a dialkyl or a diaryl disulphide was photolysed in the cavity of an e.s.r. spectrometer. The relative reactivities of the trialkylboranes and oct-1-ene were shown to be in the order Bun 3B > Bui 3B > Bus 3B > oct-1-ene > Bun 2BSBun. The absolute rate coefficients for alkylthiyldealkylation were of the same magnitude (105–107 M–1 s–1) as those found for the SH2 reactions of alkylperoxyl and alkoxyl radicals with organoboranes.

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