Triethylsilane-Dodecanethiol

The low reactivity of alkyl and/or phenyl substituted organosilanes in reduction processes can be ameliorated in the presence of a catalytic amount of alkanethiols. The reaction mechanism is reported in Scheme 5 and shows that alkyl radicals abstract hydrogen from thiols and the resulting thiyl radical abstracts hydrogen from the silane. This procedure, which was coined polarity-reversal catalysis, has been applied to dehalogenation, deoxygenation, and desulfurization reactions.For example, 1-bromoadamantane is quantitatively reduced with 2 equiv of triethylsilane in the presence of a catalytic amount of ferf-dodecanethiol. 

The reduction of the 6-bromohex-l-ene was performed by heating at 80°C a degassed solution of dilauroyl peroxide (0.004 M), triethylsilane (1.5 M), unsaturated bromide (0.0386M), dodecanethiol ( 0.003 M) or thiol supported polymer(0.002 M) in heptane. 

The efficiency of this approach was first studied through the radical reduction of 1-bromoadamantane by Et3SiH in presence of the polyHIPE-supported thiol catalyst (table l).The conversion of 1-bromoadamantane is complete after 1 hour at 80°C with a catalytic amount of dodecanethiol and two equivalents of triethylsilane. In the same conditions, 70% of the bromide were reduced in the presence of the supported thiol, showing a lower reactivity of this last one. The absence of reduction without thiol proved the role of the supported thiol. 

A low conversion of 6-bromohex-l-ene, without formation of the expected products, was observed using dodecanethiol under low concentration of triethylsilane (table 2, entry 1). Roberts and his coworkers10, pointed out the weak efficiency of a similar... 

An alternative procedure for the reduction of xanthates, as proposed by Roberts and co-workers, was to employ a catalytic amount of a thiol, in combination with triethylsilane. Using 1,1-di-f-butyl peroxide (DTBP) as radical initiator, /-dodecanethiol as an acceptor polarity-reversal catalyst, followed by triethylsilane as stoichiometric reductant. The thiol serves to transfer H-atom from the silane reductant to the intermediate radical species (R-). "... 

---