Stannylated Vinylic Addition Polynorbornene: Probing a Reagent for Friendly Tin-mediated Radical Processes

Vinylic addition polynorbornenes (VA-PNB) with stannyl functional groups have been prepared and used in tin-mediated radical dehalogenation reactions. The aliphatic and robust scaffold of VA-PNB is well suited for a support in radical processes. VA-PNB-(CH2)nSnHBu2 can be used as stoichiometric reagent and VA-PNB-(CH2)nSnBu2Cl as catalyst in the presence of a hydride donor for the reduction of RBr. The mixture KF(aq)/PMHS is the most convenient hydride source to generate VA-PNB-(CH2)nSnHBu2 in situ. Although quite popular in this context, boron hydrides, being a source of radicals themselves, are not adequate to correctly evaluate the performance of the anchored organotin group. VA-PNB-(CH2)4SnBu2Cl can be recycled and, even if it loses activity upon reuse, it is still useful after ten cycles. The stannylated VA-PNB can be separated from the products by simple filtration and it affords a very low tin contamination (at least 250 times lower than that using conventional separation methods).

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