Soluble polyethylene- and polystyrene-bound tin halides as catalysts for reductions of alkyl and aryl bromides and iodides by sodium borohydride

The synthesis, characterization, and use of soluble polyethylene- and polystyrene-bound tin chlorides as catalysts for the reduction of alkyl halides using a suspension of sodium borohydride in toluene and a crown ether as a phase-transfer catalyst are described. These tin-containing soluble macromolecules were synthesized by anionic oligomerization of ethylene or styrene followed by electrophilic substitution of the resulting living oligomer with various organic tin halides including tin tetrachloride, n-butyltin trichloride, di-n-butyltin dichloride, and diphenyltin dichloride. The resulting oligomer-bound tin reagents were characterized by {sup 1}H and {sup 119}Sn NMR spectroscopy, and the tin content of the oligomers was analyzed by ICP analysis. Typically the tin reagents were used as cocatalysts (ca. 10%) along with 10-20% of a crown ether as a phase-transfer catalyst in reductions of primary, secondary, and aryl halides using a suspension of sodium borohydride in hot toluene at 110{degree}C. Kinetic studies showed that the reaction rate was dependent on the concentration of the tin catalyst and that secondary halides reacted slightly faster than primary halides.