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

Abstract

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 a stoichiomet- ric reagent and VA-PNB-(CH2)nSnBu2Cl as a catalyst in the pres- ence of a hydride donor for the reduction of RBr. The mixture KF (aq.)/polymethylhydrosiloxane (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 leads to very low tin contamination (at least 250 times lower than that with use of conventional separation methods).