Poly(ω-bromoalkylnorbornenes-co-norbornene) by ROMP-hydrogenation: a robust support amenable to post-polymerization functionalization

Abstract

ARTICLEThis journal is © The Royal Society of Chemistry 2013 J. Name., 2013 Rodrigo García-Loma and Ana C. Albéniz*The ring opening metathesis copolymerization of norbornene and ω-bromoalkylnorbornenes NB-(CH2)nBr (n = 1, 4) by Grubbs' 2nd generation catalyst, followed by hydrogenation, gives insoluble saturated polynorbornenes (ROMPH-PNBs) that have pendant ω-bromoalkyl chains (4a, b). These materials can be functionalized by nucleophilic substitution of bromide to give a variety of substituted polymers (ROMPH-PNB-(CH2)nNu where Nu = CN, SPh, OOCMe, N3, SnR3. The stannylated polymers were tested in a Pd-catalyzed reaction, the Stille coupling. The azido polynorbornenes ROMPH-PNB-(CH2)nN3easily undergo the click 1,3-dipolar cycloaddition with alkynes, which could be a useful strategy to anchor other functionalities of interest. The aliphatic nature of the ROMPH-PNB-(CH2)nBr backbone makes robust supports and the presence of the bromo substituent imparts versatility so they are good candidates to be used as a general starting material to anchor a group required for a specific synthetic purpose.

Vinylic Addition Polynorbornene as Support for N‐Heterocyclic Carbene Palladium Complexes: Use as Reservoir of Active Homogeneous Catalytic Species in C−C Cross‐Coupling Reactions

“…The saturated polymer backbone in VA‐PNBs has a clear advantage compared with ring‐opening metathesis polymerization (ROMP)‐PNBs (Figure ), especially in metal‐catalyzed reactions. Recently, we have reported the risks of exposing the unsaturated ROMP scaffold to some metal complexes, and we have observed the insertion of the C=C double bond of ROMP‐PNB into a palladium–aryl complex, leading to the formation of an aryl‐substituted polymer . Considering the a priori attractive features of VA‐PNBs, we decided to test the behavior of the VA‐PNB skeleton as a support for palladium complexes in two cross‐coupling reactions, namely Suzuki and Negishi couplings.…”

Vinylic Addition Polynorbornene in Catalysis

“…Therefore, the synthesis of ROMPH‐PNBs does not benefit from the advantage of the wide scope of the direct ROMP polymerization of substituted norbornenes, but affords a saturated and chemically robust scaffold. This has been shown for a stannylated ROMPH‐PNB, which has been used as support of the tin reagent in the palladium catalyzed Stille coupling . This work showed that this type of scaffold behaves in a similar way to the vinylic addition polynorbornenes which, being prepared in a lower number of steps, are a more convenient choice for catalytic applications.…”

“…We have also demonstrated that the disubstituted olefins of ROMP‐PNB do insert in Pd‐aryl bonds, becoming a potential reactive center in palladium‐catalyzed cross coupling reactions. The reaction of a ROMP‐PNB with the complex [PdBr(C 6 F 5 )(NCMe) 2 ] leads to the incorporation of the pentafluorophenyl group in the polymer backbone as clearly shown by 19 F NMR (Scheme ) …”

“…ROMP‐PNBs can be converted into saturated scaffolds by hydrogenation of the double bonds in the main chain. Although the hydrogenation processes are not compatible with every functional group in the polymer, ROMP‐hydrogenated materials (ROMPH‐PNBs) bearing groups amenable to post‐polymerization functionalization have been prepared (Scheme ) . Therefore, the synthesis of ROMPH‐PNBs does not benefit from the advantage of the wide scope of the direct ROMP polymerization of substituted norbornenes, but affords a saturated and chemically robust scaffold.…”

Post-Polymerization Modification of Ring Opening Metathesis Polymerization (ROMP)-Derived Materials Using Wittig Reactions

“…The marriage of these two chemistries required the polymerization of norbornene/cyclooctene derivatives-decorated with electrophilic α-bromo ester moieties that could undergo PPMs through reactions with nucleophilic thiols. The utility of pendant alkyl bromides has been illustrated for other substitution reactions as well [39][40][41][42][43][44][45]. Following our initial reports, we reasoned that this functionality may serve as a convenient handle to introduce other useful functional groups, such as acrylates and cinnamates; these are α,β-unsaturated carbonyls that can undergo further modifications through various Michael reactions, as well as photo-facilitated [2 + 2] cycloadditions.…”