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 stoichiometric reagent and VA‐PNB‐(CH2)nSnBu2Cl as a catalyst in the presence 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).

Frustrated Lewis Pairs Catalyse the Solvent‐Assisted Synthesis of Azoles from ortho‐Substituted Anilines, CO2 and H2

“…Stoichiometric dehalogenation of aromatics with tin hydrides is well established and presumably proceeds via a radical mechanism. [47][48][49] Scheme 2. Possible pathways for benzimidazole synthesis from o-phenylenediamine, CO 2 and H 2 catalyzed by FLPs.…”

“…The remainder of the substrate was catalytically dehalogenated to benzimidazole ( 1 b ). Stoichiometric dehalogenation of aromatics with tin hydrides is well established and presumably proceeds via a radical mechanism [47–49] . In other words, hydride radicals are formed in the reaction to some extent.…”

Trispyrazolylborate Ligands Supported on Vinyl Addition Polynorbornenes and Their Copper Derivatives as Recyclable Catalysts

“…We have previously used VA‐PNB‐based polymers as supports for catalysts bearing other donor ligands such as N‐heterocyclic carbenes . We also have supported organotin reagents and used them in palladium‐catalyzed Stille couplings, and radical reactions, with good recyclability and the additional advantage of leaving a very low tin contamination in the products. From this work we have learnt that the polymer chain is robust enough to be used in catalysis and it is resistant for example to high temperature or radical processes, conditions that could compromise the performance of other type of polymeric supports.…”

Synthesis of α‐Chlorolactams by Cyanoborohydride‐Mediated Radical Cyclization of Trichloroacetamides

“…The few examples of reductive radical cyclization using grafted polymers with organotin reagents feature bromides as proradical carbon‐center species . In order to apply this chemistry to the radical cyclization of trichloroacetamides, we decided to use a stannylated polynorbornene, which was reported and recently employed by Albéniz for radical reductive bromoaryl reduction processes using polymethylhydrosiloxane (PMHS) as a reductor …”