Showing papers on "Norbornene published in 2021"
TL;DR: In this paper, a method to synthesize degradable polymers by copolymerizing 2,3-dihydrofuran with NBEs is presented.
Abstract: Norbornene derivatives (NBEs) are common monomers for living ring-opening metathesis polymerization and yield polymers with low dispersities and diverse functionalities. However, the all-carbon backbone of poly-NBEs is non-degradable. Here we report a method to synthesize degradable polymers by copolymerizing 2,3-dihydrofuran with NBEs. 2,3-Dihydrofuran rapidly reacts with Grubbs catalyst to form a thermodynamically stable Ru Fischer carbene-the only detectable active Ru species during copolymerization-and the addition of NBEs becomes rate determining. This reactivity attenuates the NBE homoaddition and allows uniform incorporation of acid-degradable enol ether linkages throughout the copolymers, which enables complete polymer degradation while maintaining the favourable characteristics of living ring-opening metathesis polymerization. Copolymerization of 2,3-dihydrofuran with NBEs gives low dispersity polymers with tunable solubility, glass transition temperature and mechanical properties. These polymers can be fully degraded into small molecule or oligomeric species under mildly acidic conditions. This method can be readily adapted to traditional ring-opening metathesis polymerization of widely used NBEs to synthesize easily degradable polymers with tunable properties for various applications and for environmental sustainability.
41 citations
TL;DR: In this article, a transition-metal-catalyzed copolymerization of olefins with polar comonomers is proposed, which is a direct strategy to access polar-functionalized polyolefins in an economical manner.
Abstract: The transition-metal-catalyzed copolymerization of olefins with polar comonomers is a direct strategy to access polar-functionalized polyolefins in an economical manner. Due to the intrinsic poisoning effect of polar groups towards Lewis acidic metal centers and the drastic reactivity differences of polar comonomers versus non-polar olefins, it is challenging to develop catalysts that provide the desired polymer molecular weight, comonomer incorporation, and activity. In this contribution, we tackle this issue from a comonomer perspective using 5,6-disubstituted norbornenes, which are highly versatile, easily accessible, inexpensive, and capable of introducing two functional groups in a single insertion. More importantly, they are only mildly poisoning due to the presence of long spacers between double bonds and polar groups, and are not prone to β-hydride elimination due to their cyclic structures. As strong π-donors, they can competitively bind to metal centers versus olefins. Indeed, phosphine-sulfonate palladium catalysts can catalyze the copolymerization of ethylene with 5,6-disubstituted norbornenes and simultaneously achieve a high polymerization activity, copolymer molecular weight, and comonomer incorporation. The practicality of this system was demonstrated by studying the properties of the resulting polymers, copolymerization in hydrocarbon solvents or in bulk, recovery/utilization of unreacted comonomer, molecular weight modulation, and large-scale synthesis.
31 citations
29 citations
TL;DR: In this paper, a three-component method is described for the synthesis of syn-1,2-disubstituted bridged bicyclic compounds, including norbornene, benzonorbornadiene, oxygen-and nitrogen-bridged analogs.
29 citations
TL;DR: In this paper, two groups of norbornene comonomers are in the context of polyolefin synthesis, and they represent an important class of comonomer in polyolefins due to their unique cyclic structures.
Abstract: Norbornene and derivatives represent an important class of comonomers in polyolefin synthesis due to their unique cyclic structures. In this contribution, two groups of norbornene comonomers are in...
28 citations
TL;DR: In this article, the authors reported a highly enantioselective kinetic resolution of tertiary benzyl alcohols via palladium/chiral norbornene cooperative catalysis with simple aryl iodides as the resolution reagent.
Abstract: Herein we report a highly enantioselective kinetic resolution of tertiary benzyl alcohols via palladium/chiral norbornene cooperative catalysis. With simple aryl iodides as the resolution reagent, a wide range of readily available racemic tertiary benzyl alcohols are applicable to this method. Both chiral tertiary benzyl alcohols and benzo[c]chromene products are obtained in good to excellent enantioselectivities (selectivity factor up to 544). The appealing synthetic utility of the obtained enantioenriched tertiary alcohols is demonstrated by the facile preparation of several valuable chiral heterocycles. Preliminary mechanism studies include DFT calculations to explain the origin of enantiodiscrimination and control experiments to uncover the formation of a transient axial chirality during the kinetic resolution step.
23 citations
TL;DR: In this article, a method to synthesize tetrahydrobenzo[b]azepines (THBAs) directly from simple aryl iodides via palladium/norbornene (Pd/NBE) cooperative catalysis is reported.
Abstract: Tetrahydrobenzo[b]azepines (THBAs) are commonly found in many bioactive compounds; however, the modular preparation of functionalized THBAs remains challenging to date. Here, we report a straightforward method to synthesize THBAs directly from simple aryl iodides via palladium/norbornene (Pd/NBE) cooperative catalysis. Capitalizing on an olefin-tethered electrophilic amine reagent, an ortho amination followed by 7-exo-trig Heck cyclization furnishes the seven-membered heterocycle. To overcome the difficulty with ortho-unsubstituted aryl iodide substrates, we discovered a unique C7-bromo-substituted NBE (N1) to offer the desired reactivity and selectivity. In addition to THBAs, synthesis of other benzo-seven-membered ring compounds can also be promoted by N1. Combined experimental and computational studies show that the C7-bromo group in N1 plays an important and versatile role in this catalysis, including promoting β-carbon elimination, suppressing benzocyclobutene formation, and stabilizing reaction intermediates. The mechanistic insights gained could guide future catalyst design. The synthetic utility has been demonstrated in a streamlined synthesis of tolvaptan and forming diverse pharmaceutically relevant THBA derivatives. Finally, a complementary and general catalytic condition to access C6-substituted THBAs from ortho-substituted aryl iodides has also been developed.
22 citations
TL;DR: In this paper, a new family of α-diimine palladium complexes that can promote norbornene polymerization at high temperatures (up to 140 °C) is disclosed.
Abstract: Increasing the thermostability of α-diimine late-transition-metal complexes and therefore rendering them more active at higher temperatures is of great importance, yet challenging for the olefin polymerization field. In the present research, a new family of α-diimine palladium complexes that can promote norbornene polymerization at high temperatures (up to 140 °C) is disclosed. Because of the conformational restriction caused by increasing the axial and equatorial bulkiness as well as the presence of intraligand H···F hydrogen bonds, N-aryl rotations can be efficiently restricted, therefore circumventing the deactivation of the active species at high temperatures. At 80-140 °C, these complexes can efficiently catalyze norbornene homopolymerizations, giving high catalytic activities up to 5.65 × 107 g of PNB per mole Ni per hour and polymers with high molecular weights up to 37.2 × 104 g/mol, which are highly superior to catalytic systems mediated by CF3-free complexes. Moreover, these complexes could also afford medium catalytic activities in the presence of polar 5-norbornene-2-carboxylic acid methyl ester (NB-COOCH3).
22 citations
TL;DR: Two-coordinate homoleptic iron complex Fe(HMTO) 2 capable of performing ring-opening metathesis polymerization of norbornene to produce highly stereoregular polynorbornene (99% cis, syndiotactic) is presented.
Abstract: Developing well-defined iron-based catalysts for olefin metathesis would be a breakthrough achievement in the field not only to replace existing catalysts by inexpensive metals but also to attain a new reactivity taking advantage of the unique electronic structure of the base metals. Here, we present a two-coordinate homoleptic iron complex, Fe(HMTO)2 [HMTO=O-2,6-(2,4,6-Me3 C6 H2 )2 C6 H3 ], that is capable of performing ring-opening metathesis polymerization of norbornene to produce highly stereoregular polynorbornene (99 % cis, syndiotactic). The use of heteroleptic Fe(HMTO)(RO) [RO=(CH3 )2 CF3 CO, CH3 (CF3 )2 CO, or Ph(CF3 )2 CO] prepared in situ significantly increases the polymerization rate while preserving selectivity. The resulting polymers were characterized by 1 H and 13 C NMR spectroscopy and gel-permeation chromatography.
22 citations
TL;DR: CB6 as discussed by the authors is a reinvigorated tethered ruthenium-benzylidene initiator that utilizes design features from ubiquitous Grubbs-type initiators that are regularly applied in linear polymerizations.
Abstract: Ring-expansion metathesis polymerization (REMP) has shown potential as an efficient strategy to access cyclic macromolecules. Current approaches that utilize cyclic olefin feedstocks suffer from poor functional group tolerance, low initiator stability, and slow reaction kinetics. Improvements to current initiators will address these issues in order to develop more versatile and user-friendly technologies. Herein, we report a reinvigorated tethered ruthenium-benzylidene initiator, CB6, that utilizes design features from ubiquitous Grubbs-type initiators that are regularly applied in linear polymerizations. We report the controlled synthesis of functionalized cyclic poly(norbornene)s and demonstrate that judicious ligand modifications not only greatly improve kinetics but also lead to enhanced initiator stability. Overall, CB6 is an adaptable platform for the study and application of cyclic macromolecules via REMP.
20 citations
TL;DR: In this paper, a series of alkene bearing small molecules were electrografted to the surface of carbon fibers using the in situ generation of aryldiazonium salts, which were used as an anchoring point for the use of Ring Opening Metathesis Polymerization (ROMP) in a 'graft from' approach to carbon fiber surface modification.
Abstract: A series of alkene bearing small molecules were electrografted to the surface of carbon fibers using the in situ generation of aryldiazonium salts. These molecules were used as an anchoring point for the use of Ring Opening Metathesis Polymerization (ROMP) in a ‘graft from’ approach to carbon fiber surface modification. After modification, evaluation of these modified fibers in an epoxy resin, using the single fiber fragmentation test, showed significant increases in interfacial shear strength (IFSS) of up to 189%, relative to untreated pristine fibers. Dilution of strained norbornene alkenes at 2:1 (alkane:alkene) had minimal effect on IFSS, while dilution at 10:1 (alkane:alkene) still resulted in improved, albeit suppressed, IFSS gains of 70% relative to pristine fibers. This study shows the potential of using ROMP as a means to tailor the surface chemistry of carbon fibers for use in advanced composites.
TL;DR: An alternate synthesis route was developed to prepare norbornene-functionalized poly(ethylene glycol) (PEG) from reacting multiarm PEG with carbic anhydride using PEGNBCA, which permits photo-cross-linking of thiol-norbornene hydrogels with kinetics comparable to conventional PEGNB macromer.
Abstract: An alternate synthesis route was developed to prepare norbornene-functionalized poly(ethylene glycol) (PEG) from reacting multiarm PEG with carbic anhydride. The macromer, PEGNBCA, permits photo-cr...
TL;DR: The longest bottlebrush polymers reported so far were synthesized in two steps from a norbornene derivative bearing two 2-bromoisobutylate moieties via atom transfer radical polymerization, which proceeded in a well-controlled manner with quantitative conversion of NB for monomer-initiator ratios ranging up to 10,000.
Abstract: The longest bottlebrush polymers reported so far (up to 7 μm in length) were synthesized in two steps from a norbornene derivative bearing two 2-bromoisobutylate moieties (NB). The key to this achievement is the excellent reactivity of NB in ring opening metathesis polymerization, which proceeded in a well-controlled manner with quantitative conversion of NB for monomer-initiator ratios ranging up to 10,000. The resultant polymer derived from NB was readily converted to various bottlebrush polymers in a divergent synthetic route by grafting vinyl monomers from the 2-bromoisobutylate units in NB via atom transfer radical polymerization. The structure of the ultra-long bottlebrush polymer was directly observed using atomic force microscopy.
TL;DR: In this paper, two traditional metallocene catalysts with conjugated diene were used for copolymerization and terpolymerization of E/P/diene conjugates.
Abstract: The copolymerization of ethylene‒diene conjugates (butadiene (BD), isoprene (IP) and nonconjugates (5-ethylidene-2-norbornene (ENB), vinyl norbornene VNB, 4-vinylcyclohexene (VCH) and 1, 4-hexadiene (HD)), and terpolymerization of ethylene-propylene-diene conjugates (BD, IP) and nonconjugates (ENB, VNB, VCH and HD) using two traditional catalysts of C2-symmetric metallocene-silylene-bridged rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 (complex A) and ethylene-bridged rac-Et(Ind)2ZrCl2 (complex B)-with a [Ph3C][B(C6F5)4] borate/TIBA co-catalyst, were intensively studied. Compared to that in the copolymerization of ethylene diene, the catalytic activity was more significant in E/P/diene terpolymerization. We obtained a maximum yield of both metallocene catalysts with conjugated diene between 3.00 × 106 g/molMt·h and 5.00 × 106 g/molMt·h. ENB had the highest deactivation impact on complex A, and HD had the most substantial deactivation effect on complex B. A 1H NMR study suggests that dienes were incorporated into the co/ter polymers' backbone through regioselectivity. ENB and VNB, inserted by the edo double bond, left the ethylidene double bond intact, so VCH had an exo double bond. Complex A's methyl and phenyl groups rendered it structurally stable and exhibited a dihedral angle greater than that of complex B, resulting in 1, 2 isoprene insertion higher than 1, 4 isoprene that is usually incapable of polymerization coordination. High efficiency in terms of co- and ter- monomer incorporation with higher molecular weight was found for complex 1. The rate of incorporation of ethylene and propylene in the terpolymer backbone structure may also be altered by the conjugated and nonconjugated dienes. 13C-NMR, 1H-NMR, and GPC techniques were used to characterize the polymers obtained.
TL;DR: A palladium/norbornene cooperative catalyzed selective C-H bond amination of aryl iodides was explored in this article, providing an efficient tool for constructing benzocyclic molecules.
TL;DR: In this paper, a review of the synthesis of high-density hydrocarbon molecules through catalytic dimerization of norbornadiene and norbornene in the past few decades, which can be used as new fuels or high-energy additives for conventional fuels is presented.
TL;DR: An efficient Rh(III)-catalyzed aerobic oxidative C-H alkenylation of arylamides with unactivated alkenes is described in this paper, where the olefination reaction was compatible with various substituted aryamides including primary, secondary, and tertiary as well as functionalized unactivated ole fins.
TL;DR: In this article, the palladium/norbornene cooperative catalysis was used to synthesize C3,C4-disubstituted indoles via the N-benzoyloxy allylamines as the coupling partner.
TL;DR: In this paper, a fluorescent poly (norbornene)-based copolymer probe P1, which was obtained via ring-opening metathesis polymerization (ROMP) of a PEG-anchored norbornene monomer NB-PEG with a rhodamine-functionalized NB-RB, has been designed and synthesized.
TL;DR: In this paper, a palladium/norbornene cooperative catalysis enabled dual-functionalization of iodinated 2-pyridones and uracils, and the success of this research depended on the use of two unique norbornene derivatives as the mediator.
Abstract: Heterocycles 2-pyridone and uracil are privileged pharmacophores. Diversity-oriented synthesis of their derivatives is in urgent need in medicinal chemistry. Herein, we report a palladium/norbornene cooperative catalysis enabled dual-functionalization of iodinated 2-pyridones and uracils. The success of this research depends on the use of two unique norbornene derivatives as the mediator. Readily available alkyl halides/tosylates and aryl bromides are utilized as ortho-alkylating and -arylating reagents, respectively. Widely accessible ipso-terminating reagents, including H/DCO2Na, boronic acid/ester, terminal alkene and alkyne are compatible with this protocol. Thus, a large number of valuable 2-pyridone derivatives, including deuterium/CD3-labeled 2-pyridones, bicyclic 2-pyridones, 2-pyridone-fenofibrate conjugate, axially chiral 2-pyridone (97% ee), as well as uracil and thymine derivatives, can be quickly prepared in a predictable manner (79 examples reported), which will be very useful in new drug discovery. Diversity-oriented synthesis of 2-pyridone and uracil derivatives is in urgent need in medicinal chemistry as they are useful pharmacophores. Here the authors show that palladium/norbornene cooperative catalysis enabled dual-functionalization of iodinated 2- pyridones and uracils.
TL;DR: In this article, a series of anion exchange membranes of bisimidazolium functionalized triblock copolymers were synthesized by ring-opening metathesis polymerization of alkyl bromide functionalized benzonorbornadiene derivatives, 1,2-dimethyl imidazole and epoxy functionalized norbornene under the action of Grubbs 2nd catalyst.
TL;DR: In this paper, the highly regioselective ring-opening copolymerization of 5-norbornene-2,3-dicarboxylic anhydride (NA) and epoxide monomers was successfully achieved using CrIII catalyst bearing tetradentate imine-thioether-bridged bis(phenolate) ligand in combination with bis(triphenylphosphine)iminium chloride.
15 Oct 2021
TL;DR: A novel decarbonylative Catellani reaction via palladium-catalyzed, norbornene (NBE)-mediated polyfunctionalization of aromatic thioesters, which serve as readily available carboxylic acid derivatives, and the late-stage functionalization of a series of drug molecules highlights the potential utility of the reaction.
Abstract: The transition-metal-catalyzed decarboxylation of aryl carboxylic acids has drawn significant attention as an efficient and practical tool for the synthesis of substituted arenes. However, the decarboxylative construction of polysubstituted arenes with different contiguous substituents has not been widely reported. Herein, we describe a novel decarbonylative Catellani reaction via palladium-catalyzed, norbornene (NBE)-mediated polyfunctionalization of aromatic thioesters, which serve as readily available carboxylic acid derivatives. A variety of alkenyl, alkyl, aryl, and sulfur moieties could be conveniently introduced into the ipso-positions of the aromatic thioesters. By combining carboxyl-directed C-H functionalization and the classical Catellani reaction, our protocol allows for the construction of 1,2,3-trisubstituted and 1,2,3,4-tetrasubstituted arenes from simple aromatic acids. Furthermore, the late-stage functionalization of a series of drug molecules highlights the potential utility of the reaction.
TL;DR: In this article, a norbornene-based reaction-triggered ESIPT active probe (NT) was developed for 1,3-dithiolane desulfurization.
Abstract: Mercury (Hg2+)-triggered desulfurization of 1,3-dithiolane to the formyl group formation process has been utilized here to develop a norbornene-based reaction-triggered ESIPT active probe (NT). Mer...
TL;DR: In this article, it was shown that the o-iodoaniline protected by a p-methoxybenzenesulfonyl group can recover the "ortho effect" and then undergo N-S bond cleavage with vinyl palladium, thus achieving a highly selective C-N coupling reaction in the Catallani-Lautens reaction system.
TL;DR: The interest in porous organic materials derived from norbornenes is driven by versatile chemistry of norbornene, fine-tunable structure of these polymers, high accessible surface area, and large....
Abstract: The interest in porous organic materials derived from norbornenes is driven by versatile chemistry of norbornenes, fine-tunable structure of these polymers, high accessible surface area, and large ...
TL;DR: A trace mild acid-catalyzed Z → E isomerization found with stilbene derivatives fused with a norbornene moiety is presented, which constituted a unique class of molecular switches orthogonally controllable by light and acid.
Abstract: Stilbene derivatives have long been known to undergo “acid-catalyzed” Z → E isomerization, where a strong mineral acid at high concentration is practically necessary. Such severe reaction conditions often cause undesired by-reactions and limit their potential application. Herein, we present a trace mild acid-catalyzed Z → E isomerization found with stilbene derivatives fused with a norbornene moiety. By-reactions, such as the migration of the CC double bond and electrophilic addition reactions, were completely inhibited because of the ring strain caused by the fused norbornene component. Direct photolysis of the E isomers at selected wavelengths led to the E → Z photoisomerization of these stilbene derivatives and thus constituted a unique class of molecular switches orthogonally controllable by light and acid. The catalytic amount of acid could be readily removed, and the Z → E isomerization could be controlled by turning on/off the irradiation of a photoacid, which allowed repeated isomerization in a non-invasive manner. Moreover, the Z isomer produced by photoisomerization could spontaneously self-recover to the E isomer in the presence of a catalytic amount of acid. The kinetics of Z → E isomerization were adjustable by manipulating catalytic factors and, therefore, unprecedented molecular photoswitches with adjustable self-recovery were realized.
TL;DR: In this article, three new complexes with general formula of ML (M = Cu (1), Co (2), Ni (3)) containing an azo-Schiff base ligand (H2L) derived from 2,3-butanediamine and 4-(benzeneazo) salicylaldehyde were synthesized by template method.