Showing papers on "Norbornene published in 2019"
TL;DR: This Review provides a comprehensive overview of Palladium/norbornene cooperative catalysis, including the early stoichiometric investigations, catalytic reaction developments, as well as the applications in the syntheses of bioactive compounds and polymers.
Abstract: Palladium/norbornene cooperative catalysis has emerged as a distinct approach to construct polyfunctionalized arenes from readily available starting materials. This Review provides a comprehensive overview of this field, including the early stoichiometric investigations, catalytic reaction developments, as well as the applications in the syntheses of bioactive compounds and polymers. The section of catalytic reactions is divided into two parts according to the reaction initiation mode: Pd(0)-initiated reactions and Pd(II)-initiated reactions.
288 citations
TL;DR: This emerging concept of PdII /norbornene cooperative catalysis has significantly advanced Catellani-type reactions, thus enabling future developments of this field and supporting the synthesis of bioactive molecules.
Abstract: The Catellani reaction is known as a powerful strategy for the expeditious synthesis of highly substituted arenes and benzo-fused rings, which are usually difficult to access through traditional cross-coupling strategies. It utilizes the synergistic interplay of palladium and norbornene catalysis to facilitate sequential ortho C-H functionalization and ipso termination of aryl halides in a single operation. In classical Catellani-type reactions, aryl halides are mainly used as the substrates, and a Pd0 catalyst is required to initiate the reaction. Nevertheless, recent advances showcase that Catellani-type reactions can also be initiated by a PdII catalyst with different starting materials instead of aryl halides via different reaction mechanisms and under different conditions. This emerging concept of PdII /norbornene cooperative catalysis has significantly advanced Catellani-type reactions, thus enabling future developments of this field. In this Minireview, PdII -initiated Catellani-type reactions and their application in the synthesis of bioactive molecules are summarized.
127 citations
11 Feb 2019
TL;DR: A series of cross-linked anion exchange membranes (AEMs) were synthesized on the basis of the ring opening metathesis polymerization (ROMP) of norbornene monomers (rPNB) as mentioned in this paper.
Abstract: A series of cross-linked (XL) anion-exchange membranes (AEMs) were synthesized on the basis of the ring opening metathesis polymerization (ROMP) of norbornene monomers (rPNB). Poly(bromopropyl norb...
99 citations
TL;DR: A class of readily available bifunctional silyl ether-based cyclic olefins that copolymerize efficiently with norbornene-based (macro)monomers to provide copolymers with backbone degradability under mildly acidic aqueous conditions and degradation rates that can be tuned over several orders of magnitude, depending on the sily l ether substituents.
Abstract: Ring-opening metathesis polymerization of norbornene-based (macro)monomers is a powerful approach for the synthesis of macromolecules with diverse compositions and complex architectures. Nevertheless, a fundamental limitation of polymers prepared by this strategy is their lack of facile degradability, limiting their utility in a range of applications. Here we describe a class of readily available bifunctional silyl ether-based cyclic olefins that copolymerize efficiently with norbornene-based (macro)monomers to provide copolymers with backbone degradability under mildly acidic aqueous conditions and degradation rates that can be tuned over several orders of magnitude, depending on the silyl ether substituents. These monomers can be used to manipulate the in vivo biodistribution and clearance rate of polyethylene glycol-based bottlebrush polymers, as well as to synthesize linear, bottlebrush and brush-arm star copolymers with degradable segments. We expect that this work will enable preparation of degradable polymers by ROMP for biomedical applications, responsive self-assembly and improved sustainability.
93 citations
20 Mar 2019
TL;DR: Cross-linked anion exchange membranes (AEMs) synthesized by vinyl addition polymerization of norbornene were prepared for use in anion-exchange membrane electrochemical devices, including fuel.
Abstract: Cross-linked (XL) anion-exchange membranes (AEMs) synthesized by vinyl addition polymerization of norbornene were prepared for use in anion-exchange membrane electrochemical devices, including fuel...
92 citations
TL;DR: Alkenyl halide- or triflate-mediated palladium/norbornene (Pd/NBE) catalysis has been demonstrated, providing an efficient strategy for modular and regioselective construction of all-carbon tetrasubstituted olefins.
Abstract: All-carbon tetrasubstituted olefins have been found in numerous biologically important compounds and organic materials. However, regio- and stereocontrolled construction of this structural motif still constitutes a significant synthetic challenge. Here, we show that a modular and regioselective synthesis of all-carbon tetrasubstituted olefins can be realized via alkenyl halide- or triflate-mediated palladium/norbornene catalysis, which is enabled by a modified norbornene containing a C2 amide moiety. This new norbornene co-catalyst effectively suppressed undesired cyclopropanation pathways, which have previously been a main obstacle for developing such reactions. Diverse cyclic and acyclic alkenyl bromides or triflates with a wide range of functional groups can be employed as substrates. Various substituents can be introduced at the alkene C1 and C2 positions regioselectively simply by changing the coupling partners. Initial mechanistic studies provide insights on the rate-limiting step as well as the structure of the actual active ligand in this system. All-carbon tetrasubstituted olefins are challenging to prepare in a regio- and stereocontrolled fashion. Now, using an amide-substituted norbornene as a co-catalyst, alkenyl halide- or triflate-mediated palladium/norbornene (Pd/NBE) catalysis has been demonstrated, providing an efficient strategy for modular and regioselective construction of all-carbon tetrasubstituted olefins.
75 citations
TL;DR: In this article, aryl iodides and unsaturated carboxylic acid anhydrides are used as substrates for indenone-based natural products, such as pauciflorol F and acredinone A.
Abstract: To show the synthetic utility of palladium/norbornene (Pd/NBE) cooperative catalysis, here we report concise syntheses of indenone-based natural products, pauciflorol F and acredinone A, which are enabled by direct annulation between aryl iodides and unsaturated carboxylic acid anhydrides. Compared to the previous indenone-preparation approaches, this method allows simple aryl iodides to be used as substrates with complete control of the regioselectivity. The total synthesis of acredinone A features two different Pd/NBE-catalyzed ortho acylation reactions for constructing penta-substituted arene cores, including the development of a new ortho acylation/ipso borylation.
57 citations
TL;DR: It has been shown that a degenerative reversible chain-transfer process enables the synthesis of ring-opened metathesis polymers with controlled molecular weight, using only catalytic amounts of a ruthenium complex.
Abstract: In a conventional living ring-opening metathesis polymerization (ROMP), an equal number of ruthenium complexes to the number of polymer chains synthesized are required. This can lead to high loadings of ruthenium complexes when aiming for shorter polymers. Here, a reversible chain-transfer agent was used to produce living ROMP polymers from norbornene derivatives using catalytic amounts of Grubbs' ruthenium complexes. The polymers obtained by this method showed all of the characteristics of a living polymerization (that is, good molecular weight control, narrow molecular weight dispersities and the ability to form block copolymers). Monomers carrying functional moieties such as ferrocene, coumarin or a triisopropylsilyl-protected primary alcohol could also be catalytically polymerized in a living fashion. The method presented follows a degenerative chain-transfer process and is more economical and environmentally friendly compared with previous living ROMP procedures as it utilizes only catalytic amounts of costly and toxic ruthenium complexes.
56 citations
TL;DR: The monomeric molecular aluminium(i) complex 1 [{(ArNCMe)2CH}Al] (Ar = 2,6-di-iso-propylphenyl) reacts with a series of terminal and strained alkenes including ethylene, propylene, allylbenzene and norbornene to form alkene bound products.
Abstract: The monomeric molecular aluminium(I) complex 1 [{(ArNCMe)2CH}Al] (Ar = 2,6-di-iso-propylphenyl) reacts with a series of terminal and strained alkenes including ethylene, propylene, allylbenzene and norbornene to form alkene bound products. Remarkably all these reactions are reversible under mild conditions (298–353 K) with alkene binding being disfavoured at higher temperatures due to the positive reaction entropy. Van't Hoff analyses have allowed quantification of the binding events with . Calculations and single crystal X-ray diffraction studies are consistent with the alkene bound species being metallocyclopropane complexes. Alkene binding involves a reversible redox process with changes from the +1 to +3 aluminium oxidation state. Under more forcing conditions the metallocyclopropane complexes undergo non-reversible allylic C–H bond activation to generate aluminium(III) allyl hydride complexes. This represents a rare example of redox-based main group reactivity in which reversible substrate binding is followed by a further productive bond breaking event. Analysis of the mechanism reveals a reaction network in which alkene dissociation and reformation of 1 is required for allylic C–H activation, a realisation that has important implications for the long-term goal of developing redox-based catalytic cycles with main group compounds.
50 citations
TL;DR: In this article, a new biobased functional norbornene was synthesized by the Diels-Alder reaction between cyclopentadiene and the fluorinated eugenol.
Abstract: A new biobased functional norbornene was synthesized by the Diels–Alder reaction between cyclopentadiene and the fluorinated eugenol. Based on the norbornene monomer, a new polynorbornene was prepared with a high molecular weight (Mn = 78 000 Da) by the standard ring opening metathesis polymerization (ROMP). This polymer displayed good film-forming ability and can be postpolymerized to form a cross-linked network at high temperature (>150 °C) via the [2 + 2] cycloaddition reaction of trifluorovinyl ether (−OCF2═CF2) groups. The cross-linked polymer exhibited good transmittance (T % > 90% at 550 nm) and high thermostability with a 5% weight loss temperature of 412 °C. Moreover, no obvious glass transition temperature (Tg) was observed in the DMA measurement when the temperature was elevated near the decomposition temperature of the cross-linked polymer (about 350 °C). The cured resin displayed an average dielectric constant (Dk) of below 2.65 with average dissipation factor (Df) of 4.3 × 10–3 for the frequ...
48 citations
TL;DR: The high activity of the radical NPs as chemoselective and homogeneous, yet readily recyclable catalysts is demonstrated through oxidation of a variety of alcohols and recovery by simple centrifugation.
Abstract: We report the straightforward, time-efficient synthesis of radical core-shell nanoparticles (NPs) by polymerization-induced self-assembly. A nitroxide-containing hydrophilic macromolecular precursor was prepared by ring-opening metathesis copolymerization of norbornenyl derivatives of TEMPO and oligoethylene glycol and was chain-extended in situ with norbornene in ethanolic solution, leading to simultaneous amphiphilic block copolymer formation and self-assembly. Without any intermediate purification from the monomers to the block copolymers, radical NPs with tunable diameters ranging from 10 to 110 nm are obtained within minutes at room temperature. The high activity of the radical NPs as chemoselective and homogeneous, yet readily recyclable catalysts is demonstrated through oxidation of a variety of alcohols and recovery by simple centrifugation. Furthermore, the NPs show biocompatibility and antioxidant activity in vitro.
TL;DR: The results presented here add to the body of mechanistic work for olefin metathesis and may inform the continued design of catalysts for ROMP to access new polymer architectures and materials.
Abstract: The mechanism of Ru-catalyzed ring-opening metathesis polymerization (ROMP) is studied in detail using a pair of third generation ruthenium catalysts with varying sterics of the N-heterocyclic carbene (NHC) ligand. Experimental evidence for polymer chelation to the Ru center is presented in support of a monomer-dependent mechanism for polymerization of norbornene monomers using these fast-initiating catalysts. A series of kinetic experiments, including rate measurements for ROMP, rate measurements for initiation, monomer-dependent kinetic isotope effects, and activation parameters were useful for distinguishing chelating and nonchelating monomers and determining the effect of chelation on the polymerization mechanism. The formation of a chelated metallacycle is enforced by both the steric bulk of the NHC and by the geometry of the monomer, leading to a ground-state stabilization that slows the rate of polymerization and also alters the reactivity of the propagating Ru center toward different monomers in copolymerizations. The results presented here add to the body of mechanistic work for olefin metathesis and may inform the continued design of catalysts for ROMP to access new polymer architectures and materials.
TL;DR: In this article, a plan, initial design and revised strategy in the enantioselective synthesis of the rhazinal family of natural products were discussed, along with the α-acylation reaction by the cleavage of various C(O)-X bonds.
Abstract: This account focuses on our work in palladium/norbornene-catalyzed selective ortho-arylation and ortho-acylation of aryl halides. It will discuss our synthetic plan, initial design and revised strategy in the enantioselective synthesis of the rhazinal family of natural products. It also shows our efforts on the α-acylation reaction by the cleavage of various C(O)–X bonds, along with some mechanistic studies. 1 Introduction 2 Synthesis of the Rhazinal Family of Natural Products 2.1 Initial Design 2.2 Revised Strategy 2.3 Enantioselective Synthesis of the Rhazinal Family of Natural Products 3 Catalytic ortho-Acylation 3.1 Acid Chloride and Anhydride Strategy 3.2 Cleavage of C(O)–S Bond of Thioesters by Pd, Norbornene and Copper Cocatalysis 4 Decarboxylative Alkynylation 5 Conclusion
TL;DR: A sulfenamide-enabled ortho-thiolation of aryl iodides via Pd/norbornene cooperative catalysis for the preparation of polysubstituted aromatic sulfur compounds is developed.
Abstract: Poly-substituted aromatic sulfur compounds are widely found in pharmaceuticals, agrochemicals and organic materials. However, the position that a sulfur moiety can be introduced to is largely restricted to a pre-functionalized site; otherwise, use of electronically biased substrates or auxiliary groups that direct catalysis is required. Here we report a general ortho thiolation of common aryl and heteroaryl iodides via palladium-norbornene cooperative catalysis. Using this approach, an aryl or alky sulfur moiety can be site-selectively introduced at the arene ortho position without using sterically or electronically biased substrates. The arene ipso functionalization is simultaneously achieved through Heck, Suzuki or Sonogashira termination. The reaction is enabled by a unique class of electrophiles in palladium-norbornene cooperative catalysis, which are sulfenamides derived from seven-membered lactams. The broad substrates scope and high chemoselectivity could make this method attractive for synthesis of complex sulfur-containing aromatic compounds. Poly-substituted aromatic sulfur compounds are part of many pharmaceuticals, agrochemicals and organic materials. Here, the authors developed a sulfenamide-enabled ortho-thiolation of aryl iodides via Pd/norbornene cooperative catalysis for the preparation of polysubstituted aromatic sulfur compounds.
TL;DR: A palladium/norbornene-catalyzed chemoselective ortho thiolation of aryl halides was reported, showing good substrate scope: both S-alkyl and S-aryl thiosulfonates were compatible.
TL;DR: The nickel-catalyzed reaction of aromatic amides that contain an 8-aminoquinoline as a directing group with bicyclic alkenes, such as norbornene and 1,4-dihydro-1, 4-epoxynaphthalene, results in the cleavage of both the C-H bond at the ortho-position of the benzene ring and the C(O)-N bond to give methanofluoren-9-one
TL;DR: This work describes the use of a Cu(I) precatalyst that achieves selective olefin activation via coordination to the metal center and engages alkyl ketones, which are more challenging to accommodate via direct irradiation pathways.
Abstract: Photocycloadditions are often typified by the oxetane-forming Paterno-Buchi reaction. However, the mechanistic constraints of carbonyl excitation and olefin interception have limited this attractive oxetane-forming pathway. Here we describe the use of a Cu(I) precatalyst that achieves selective olefin activation via coordination to the metal center. Significantly, this intermolecular 2 + 2 carbonyl-olefin photocycloaddition engages alkyl ketones, which are more challenging to accommodate via direct irradiation pathways. Mechanistic investigations support the in situ formation of a Cu-norbornene resting state that undergoes a MLCT leading to oxetane formation.
TL;DR: It is settled that the mechanistic route taken by any substrate in the sequential tandem cycloaddition reaction of functionalized acetylenes with cyclopentadiene and dimethyl diazopropane for the formation of norbornene pyrazolines is greatly affected by both electronic and steric factors.
Abstract: The mechanistic pathways for the sequential tandem [4 + 2] / [3 + 2] versus [3 + 2] / [4 + 2] cycloaddition reaction of functionalized acetylenes with cyclopentadiene and dimethyl diazopropane for the formation of norbornene pyrazolines, employed in the synthesis of pharmaceutically relevant compounds, have been studied computationally with DFT at the M06-2X/6-31G(d) and M06-2X/6-31G(d,p) levels of theory. We have established that, in the reaction of the parent (unsubstituted) acetylene with cyclopentadiene and dimethyl diazopropane, the order of the tandem addition has no substantial effects in product outcomes. The same product is obtained provided the reaction components remain the same for both [4 + 2]/[3 + 2] and [3 + 2]/[4 + 2] tandem addition sequences. The results indicate that the [4 + 2] Diels–Alder addition step is the rate-determining step irrespective of the addition order, while the 1,3-dipolar cycloaddition step has been found to generally proceed rapidly with very low activation energies. It has also been realized that the regio-, stereo-, and chemo-selectivities of the reaction are strictly dictated by the type of substituent on the parent acetylene. For substituted acetylenes, we conclude that the sequence of the tandem addition generally affects the type of isomeric product obtained. The [4 + 2]/[3 + 2] tandem addition sequence has been established to favor the exo stereo-selective isomer over the endo, whereas the [3 + 2]/[4 + 2] tandem addition sequence generally favors the endo product formation. Therefore, it is settled that the mechanistic route taken by any substrate in the [4 + 2]/[3 + 2] versus [3 + 2]/[4 + 2] sequential tandem cycloaddition is greatly affected by both electronic and steric factors. Electrophilicity indices calculations agree with the activation barriers obtained. Perturbation molecular orbital theory was employed to rationalize the results. Global reactivity indices calculations gave a good correlation with the activation energies.
TL;DR: In this article, a new heterogeneous nanocatalyst (Fe3O4@SiO2-Schiff base-Co(II)) was successfully fabricated applying silica-coated magnetite nanoparticles as a suitable and efficient support for covalent anchoring of a cobalt(II) Schiff base complex.
28 Aug 2019
TL;DR: In this paper, the authors proposed that the poor processability of phthalonitrile polymers is the main reason for the poor flame retardancy of polyethylene polymers.
Abstract: Phthalonitrile polymers exhibit many attractive advantages including high thermal and mechanical properties, low water absorptivity, and excellent flame retardancy. However, the poor processability...
TL;DR: Norbornene derivatives were validated as probes for cysteine sulfenic acid on proteins and in live cells and revealed a different reactivity profile than the traditional dimedone reagent.
Abstract: Norbornene derivatives were validated as probes for cysteine sulfenic acid on proteins and in live cells. Trapping sulfenic acids with norbornene probes is highly selective and revealed a different reactivity profile than the traditional dimedone reagent. The norbornene probe also revealed a superior chemoselectivity when compared to a commonly used dimedone probe. Together, these results advance the study of cysteine oxidation in biological systems.
TL;DR: A redox-neutral ortho functionalization of aryl boroxines via Pd/NBE catalysis, which avoids stoichiometric bases or acids, thereby tolerating a wide range of functional groups and could inspire the development of a new class of Pd-NBE-catalyzed transformations.
TL;DR: In this paper, the Bruker Avance III 400 (400MHz for 1H, 101MHz for 13C) spectrometer was used to record the NMR spectra of the time of flight mass spectrometers.
Abstract: All primary data files for the publication can be found here. Procedures, reaction conditions and used analytical equipment is discussed in detail in the experimental section or the supporting information of the paper. Nuclear magnetic resonance (NMR) Spectra are named according to the numbering in the publication. ¹H-NMR, ¹⁹F-NMR and ¹³C-NMR spectra were recorded using a Bruker Avance III 400 (400MHzfor 1H, 101MHz for 13C) spectrometer. NMR files can be opened with software such as MestReNova or TopSpin. Size exclusion chromatography (SEC) and Matrix Assisted Laser Desorption Ionization - Time of Flight Mass Spectrometry (MALDI-TOF-MS) data are provided as text-files and can be plotted with software such as MS Excel.
TL;DR: A direct vicinal difunctionalization of thiophenes via the palladium/norbornene (Pd/NBE) cooperative catalysis is reported, enabled by an arsine ligand and a unique amide-based NBE.
Abstract: Herein we report a direct vicinal difunctionalization of thiophenes via the palladium/norbornene (Pd/NBE) cooperative catalysis. A series of mono- and disubstituted thiophenes can be difunctionalized site-selectively and regioselectively at the C4 and C5 positions in good yields, enabled by an arsine ligand and a unique amide-based NBE. The synthetic utility has been shown in derivatizations of complex bioactive compounds and an open-flask gram-scale preparation. Preliminary results have been obtained in the difunctionalization of furans and a direct C4-selective arylation of 2-substituted thiophenes.
TL;DR: In this paper, the authors used density functional theory (DFT) to determine the initial Mg-H/C[double bond, length as m-dash]C insertion process at the intact magnesium hydride dimer.
Abstract: The dimeric β-diketiminato magnesium hydride, [(BDI)MgH]2, reacts at 80 °C with the terminal alkenes, 1-hexene, 1-octene, 3-phenyl-1-propene and 3,3-dimethyl-butene to provide the respective n-hexyl, n-octyl, 3-phenylpropyl and 3,3-dimethyl-butyl magnesium organometallics. The facility for and the regiodiscrimination of these reactions are profoundly affected by the steric demands of the alkene reagent. Reactions with the phenyl-substituted alkenes, styrene and 1,1-diphenylethene, require a more elevated temperature of 100 °C with styrene providing a mixture of the 2-phenylethyl and 1-phenylethyl products over 7 days. Although the reaction with 1,1-diphenylethene yields the magnesium 1,1-diphenylethyl derivative as the sole reaction product, only 64% conversion was achieved over a 21 day timeframe. Reactions with the α,ω-dienes, 1,5-hexadiene and 1,7-octadiene, provided divergent results. The initial 5-alkenyl magnesium reaction product of the shorter chain diene undergoes 5-exo-trig cyclisation via intramolecular carbomagnesiation to provide a cyclopentylmethyl derivative, which was shown by X-ray diffraction analysis to exist as a three-coordinate monomer. In contrast, 1,7-octadiene provided a mixture of two compounds, a magnesium oct-7-en-1-yl derivative and a dimagnesium-octane-1,4-diide, as a result of single or two-fold activation of the terminal C[double bond, length as m-dash]C double bonds. The magnesium hydride was unreactive towards internal alkenes apart from the strained bicycle, norbornene, allowing the characterisation of the resultant three-coordinate magnesium norbornyl derivative by X-ray diffraction analysis. Computational analysis of the reaction between [(BDI)MgH]2 and 1-hexene using density functional theory (DFT) indicated that the initial Mg-H/C[double bond, length as m-dash]C insertion process is rate determining and takes place at the intact magnesium hydride dimer. This exothermic reaction (ΔH = -14.1 kcal mol-1) traverses a barrier of 18.9 kcal mol-1 and results in the rupture of the dinuclear structure into magnesium alkyl and hydride species. Although the latter three-coordinate hydride derivative may be prone to redimerisation, it can also provide a further pathway to magnesium alkyl species through its direct reaction with a further equivalent of 1-hexene, which occurs via a lower barrier of 15.1 kcal mol-1. This Mg-H/C[double bond, length as m-dash]C insertion reactivity provides the basis for the catalytic hydrosilylation of terminal alkenes with PhSiH3, which proceeds with a preference for the formation of the anti-Markovnikov organosilane product. Further DFT calculations reveal that the catalytic reaction is predicated on a sequence of Mg-H/C[double bond, length as m-dash]C insertion and classical Si-H/Mg-C σ-bond metathesis reactions, the latter of which, with a barrier height of 24.9 kcal mol-1, is found to be rate determining.
TL;DR: In this article, the application of C1-symmetrical diphosphite ligands containing furanose backbone in the Rh-catalysed asymmetric hydroformylation of norbornene is described.
Abstract: The application of C1‐symmetrical diphosphite ligands containing furanose backbone in the Rh‐catalysed asymmetric hydroformylation of norbornene is described. The catalysts were highly active and produced exclusively exo‐norbornanecarboxaldehyde with enantioselectivities (ee) up to 71 %. Considering these promising results, the ligands were modified with a pyrene moiety to accomplish their immobilisation onto carbon materials. The corresponding Rh complexes bearing the novel pyrene‐tagged ligands were synthesised and immobilised onto multiwalled carbon nanotubes (MWCNT), reduced graphene oxide (rGO) and carbon beads (CBs). The novel catalytic systems were tested in the asymmetric hydroformylation of norbornene providing similar performance in terms of both activity and selectivity compared to the non‐immobilised systems. The recyclability of the new heterogenised catalysts was studied in the target reaction in batch mode. Nevertheless, the recycling was unsuccessful due to catalyst leaching. When used under continuous flow mode, these catalysts revealed robust and provided even higher ee than the corresponding homogeneous systems.
TL;DR: A set of diarylamido-based unsymmetrical pincer ligands containing a chiral oxazoline ring have been synthesized and their nickel and palladium complexes were tested to show high catalytic activities for polymerization of norbornene.
Abstract: A set of diarylamido-based unsymmetrical [PNNox] pincer ligands containing a chiral oxazoline ring have been synthesized and their nickel and palladium complexes [(2-PPh2(R1)ArN(R1)Ar-2-(R)oxazoline)MCl] (R1 = 4-H, R = (S)-4-iPr, M = Pd (Pd1); R1 = 4-H, R = (S)-4-Bn, M = Pd (Pd2); R1 = 4-H, R = (S)-4-Ph, M = Pd (Pd3); R1 = 4-Me, R = (S)-4-Bn, M = Pd (Pd4); R1 = 4-Me, R = (S)-4-Ph, M = Pd (Pd5); R1 = 4-H, R = 4-Me2, M = Pd (Pd6); R1 = 4-H, R = Benzo[d]-, M = Pd (Pd7); R1 = 4-H, R = (S)-4-Bn, M = Ni (Ni1); R1 = 4-H, R = (S)-4-Ph, M = Ni (Ni2); R1 = 4-Me, R = (S)-4-Bn, M = Ni (Ni3); R1 = 4-Me, R = (S)-4-Ph, M = Pd (Ni4)) were tested to show high catalytic activities for polymerization of norbornene. After activation of methylaluminoxane (MAO), all the nickel and palladium complexes could catalyze the polymerization of norbornene to yield vinyl-type polymers with activities up to 40.3 × 105 g of PNB (mol of Pd)−1 h−1. The copolymerization of norbornene with functional norbornene comonomers was also investigated by catalyst Pd2, accompanied by decreased catalytic activity and low incorporation of functional comonomers.
TL;DR: A facile route to bring DNA to the organic phase, which greatly expands the types of structures accessible using DNA macromonomers and demonstrates substantial simplification in the preparation of traditionally difficult DNA-containing structures, such as DNA/poly(ethylene glycol) diblock graft copolymers and DNA amphiphiles.
TL;DR: This work shows by means of quantum chemical calculations and experiments that the chloroalkynylation of 1,1-disubstituted alkenes can be successfully achieved via gold(I) catalysis and is an attractive method en route to complex alkynes and their congeners.
Abstract: The haloalkynylation reaction is of great interest for the synthesis of complex molecules as it represents a carbon-carbon bond-forming reaction where the reactive halide reappears in the product. The latter enables further chemical transformations. However, only a few examples of haloalkynylations have been described so far. By using alkenes as reactant, this reaction is strictly limited to norbornene systems proceeding via a nonclassical carbocation. Herein, we show by means of quantum chemical calculations and experiments that the chloroalkynylation of 1,1-disubstituted alkenes can be successfully achieved via gold(I) catalysis. The key step in the reaction mechanism is a 1,3-chlorine shift to a cationic center, leading selectively to the corresponding homopropargyl chlorides. As this gold(I)-catalyzed addition can be conducted on a preparative scale and tolerates a broad substrate scope of both alkyne and alkene reactants, the presented chloroalkynylation reaction is an attractive method en route to complex alkynes and their congeners.
TL;DR: The PNN and NNN complexes exhibited far greater activity on the order of 107 g of PNB/mol/h, with quantitative yields in some cases, in comparison to the PNP pincer palladium and nickel complexes, and this trend was also supported by the iPr group substituted PNP nickel and palladium pincers.
Abstract: Unsymmetrical pincers have been shown to be better than the corresponding symmetrical pincers in several catalysis reactions. A new unsymmetrical PNN propincer, 2-(3,5-dimethylpyrazolylmethyl)-5-(diphenylphosphinomethyl)pyrrole (1), was synthesized from pyrrole through Mannich bases in a good yield. In addition, the new byproduct 2-(3,5-dimethylpyrazolylmethyl)-5-(dimethylaminomethyl)-N-(hydroxymethyl)pyrrole was also isolated. The reaction of 1 with [PdCl2(PhCN)2] and Et3N in toluene yielded [PdCl{C4H2N-2-(CH2Me2pz)-5-(CH2PPh2)-κ3P,N,N}] (2). The analogous reaction between 1 and [NiCl2(DME)] or NiX2 (X = Br, I) in the presence of NEt3 in acetonitrile afforded [NiX{C4H2N-2-(CH2Me2pz)-5-(CH2PPh2)-κ3P,N,N}] (3; X = Cl, Br, I). All complexes were structurally characterized. The norbornene polymerization behaviors of the unsymmetrical pincer complexes 2 and 3 in the presence of MMAO or EtAlCl2 were compared with those of the symmetrical pincer complexes chloro[2,5-bis(3,5-dimethylpyrazolylmethyl)pyrrolido]pal...