Showing papers on "Norbornadiene published in 2014"

Total Synthesis of Gracilioether F: Development and Application of Lewis Acid Promoted Ketene-Alkene [2+2] Cycloadditions and Late-Stage CH Oxidation

Abstract: The first synthesis of gracilioether F, a polyketide natural product with an unusual tricyclic core and five contiguous stereocenters, is described. Key steps of the synthesis include a Lewis acid promoted ketene–alkene [2+2] cycloaddition and a late-stage carboxylic acid directed C(sp3)H oxidation. The synthesis requires only eight steps from norbornadiene.

Stereospecific ring-opening metathesis polymerization of norbornadienes employing tungsten oxo alkylidene initiators.

Abstract: We report here the polymerization of several 7-isopropylidene-2,3-disubstituted norbornadienes, 7-oxa-2,3-dicarboalkoxynorbornadienes, and 11-oxa-benzonorbornadienes with a single tungsten oxo alkylidene catalyst, W(O)(CH-t-Bu)(OHMT)(Me2Pyr) (OHMT = 2,6-dimesitylphenoxide; Me2Pyr = 2,5-dimethylpyrrolide) to give cis, stereoregular polymers. The tacticities of the menthyl ester derivatives of two polymers were determined for two types. For poly(7-isopropylidene-2,3-dicarbomenthoxynorbornadiene) the structure was shown to be cis,isotactic, while for poly(7-oxa-2,3-dicarbomenthoxynorbornadiene) the structure was shown to be cis,syndiotactic. A bis-trifluoromethyl-7-isopropylidene norbornadiene was not polymerized stereoregularly with W(O)(CHCMe2Ph)(Me2Pyr)(OHMT) alone, but a cis, stereoregular polymer was formed in the presence of 1 equiv of B(C6F5)3.

Flexible Coordination of Diphosphine Ligands Leading to cis and trans Pd(0), Pd(II), and Rh(I) Complexes

Abstract: A series of diphosphine ligands iPr2P–C6H4–X–C6H4–PiPr2 (for ligand L1, X = CH2; for ligand L2, X = CH2CH2) was investigated to determine the preference for cis/trans coordination to palladium(0), palladium(II), and rhodium(I). Increasing the length of the bridging alkyl backbone from one to two carbons changes the geometry of the resulting palladium(II) complexes, with L1 coordinating preferentially cis, while L2 coordinates in a trans fashion. Coordination to Pd(0) leads to L1Pd(dba) and L2Pd(dba), in which both ligands accommodate a P–M–P angle close to 120°. L2 was found to coordinate cis in a rhodium(I) complex ([L2Rh(nbd)][BF4], where nbd = norbornadiene).

First Stabilization of 14‐Electron Rhodium(I) Complexes by Hemichelation

Abstract: Hemichelation is emerging as a new mode of coordination where non-covalent interactions crucially contribute to the cohesion of electron-unsaturated organometallic complexes. This study discloses an unprecedented demonstration of this concept to a Group 9 metal, that is, RhI. The syntheses of new 14-electron RhI complexes were achieved by choosing the anti-[(η6:η6-fluorenyl){Cr(CO)3}2] anion as the ambiphilic hemichelating ligand, which was treated with [{Rh(nbd)Cl}2] (nbd=norbornadiene) and [{Rh(CO)2Cl}2]. The new T-shaped RhI hemichelates were characterized by analytical and structural methods. Investigations using the methods of the DFT and electron-density topology analysis (NCI region analysis, QTAIM theory) confirmed the closed-shell, non-covalent and attractive characters of the interaction between the RhI center and the proximal Cr(CO)3 moiety. This study shows that, by appropriate tuning of the electronic properties of the ambiphilic ligand, truly coordination-unsaturated RhI complexes can be synthesized in a manageable form.

N-Heterocyclic carbene rhodium(I) complexes containing an axis of chirality: dynamics and catalysis

Abstract: The novel rhodium(I) complexes [RhCl(NBD)(NHC)] [NBD = norbornadiene, NHC = 1-benzyl-3-R-imidazolin-2-ylidene; R = Me (3a), Bz (3b), Tr (3c), tBu (3d)], containing on one nitrogen the benzyl substituent and on the other increasing bulky alkyl substituents were prepared. All the complexes display restricted rotation around the metal–carbene bond and yield conformational enantiomers. The stereodynamics and racemization barriers about the Rh–carbene have been determined by means of NMR spectroscopy for 3a–c, whereas for the bulkiest 3d only the lower limit (91 kJ mol−1) could be calculated. Whilst the racemization barriers obtained by DFT calculations for 3a,b and 3d matched the experimental values, in the case of 3c the latter (62.3 kJ mol−1) was much smaller with respect to the calculated one (101.7 kJ mol−1). The lower experimental barrier has been attributed to a dissociative pathway that produces a solvated ionic pair in the transition state. The catalytic activity of the neutral rhodium(I) complexes 3a and 3d in the hydrosilylation with HSiMe2Ph of the terminal alkynes PhC≡CH, TolC≡CH, nBuC≡CH, Et3SiC≡CH, and (CPh2OH)C≡CH has been investigated, and compared with the amide-functionalized [RhCl(NBD){1-(2-NHBoc-ethyl)-3-Me-imidazolin-2-ylidene}] (4) and with [RhCl(NBD){1-butyl-3-Me-imidazolin-2-ylidene}] (5).

Tuning the activity of alternative Ru-based initiators for ring-opening metathesis polymerization of norbornene and norbornadiene by the substituent in 4-CH2R-piperidine

Abstract: The novel [RuCl 2 (PPh 3 ) 2 (4-CH 2 R-pip)] complexes, with R = H (complex 1 ), Ph ( 2 ) or OH ( 3 ), were synthesized and applied as initiators for ROMP of norbornene (NBE) and norbornadiene (NBD) under different reaction times, temperatures and monomer concentrations. There is a clear difference in the homopolymer yields in the order 1 > 2 > 3 at [monomer]/[Ru] molar ratio of 5000, at 25 °C for 5–60 min. Difference in the yields tends to disappear at 50 °C, with quantitative yields for 15–30 min with any type of initiator. Results from copolymers obtained at RT for 60 min from fixed amounts of NBE with four different amounts of NBD suggest that the type of initiator also affects the reactions, with more insertion of NBD with 1 . The occurrence of cross-linking enhanced as the NBD loading increased, evidenced by decrease in the M c and increase in the T g values, besides the influence of the type of initiator.

The origin of exo-selectivity in methyl cyanoformate addition onto the CC bond of norbornene in Pd-catalyzed cyanoesterification

Abstract: A computational investigation has been carried out to elucidate the origin of the exclusive exo-selectivity in the Pd-catalyzed cyanoesterification of strained cyclic olefins, norbornene and norbornadiene. A hybrid density functional was selected for the level of theory with a triple-ζ quality basis set, which was proposed in an earlier study to provide an experimentally sound ground state electronic structure description for palladium(II) and palladium(IV) complexes from multi-edge X-ray absorption spectroscopic measurements. Given that the product of oxidative addition can be isolated, we focused on the olefin coordination as the earliest possible origin of exo-selectivity. The calculated geometric structure for the trans-Pd(CN)(COOR)(PPh3)2 complex at the BHandHLYP/def2TZVP/PCM(toluene) level is in an excellent agreement with its experimental structure from crystallographic measurements. Upon dissociation of one of its phosphane ligands, the coordinatively unsaturated trans-isomer is only 17 kJ mol−1 away from the isomerization transition state, leading to the 14-electron cis-isomers that are 17 to 37 kJ mol−1 lower in energy than the trans-isomers. Regardless of the initial complex for olefin coordination, the exo-isomer for the norbornene complex is at least 8 kJ mol−1 lower than the corresponding endo-isomer. The origin of this considerable difference in Gibbs free energy can be attributed to the remarkably different steric and agostic hydrogen interactions between the methylene and the ethylene bridges of the norbornene and the adjacent cis-ligands at the PdII center.

Photochemical isomerization of norbornadiene‐containing polytriazoles obtained by click chemistry polyaddition

Abstract: Polyesters and polyethers containing norbornadiene (NBD) and 1,2,3-triazole units in the main chain are prepared by step growth polymerization of diester or diether NBD-based dialkynes with different aromatic diazides using copper-catalyzed azide–alkyne cycloaddition. The solubility and the physical properties of the resulting polytriazoles are investigated by differential scanning calorimetry, thermogravimetric analysis, size exclusion chromatography, and 1H NMR spectroscopy, and are discussed taking into account of the chemical structures of the monomers. All of them are amorphous with glass transition temperatures ranging from 51 to 117 °C, number average molecular weight (Mn) values from 16 to 43 kDa and thermal degradation (Td10) values from 175 to 292 °C. The photochemical valence isomerization (PVI) of the NBD units into quadricyclanes (QC) is investigated using UV–vis spectroscopy of polymer films spin-coated onto quartz substrates. For the first time the PVI of NBD into QC is demonstrated by 1H NMR spectroscopy. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 223–231

Solar driven uphill conversion of dicyclopentadiene to cyclopentadiene: an important synthon for energy systems and fine chemicals

Abstract: The retro Diels–Alder conversion of endo-dicyclopentadiene to cyclopentadiene (Cp) – which is thermodynamically uphill under ambient conditions (ΔG = +9.7 kcal mol−1; values based on computation at 273 K following CBS-QB3 methodology) – was carried out at 175–190 °C in neat state using solar energy. The reaction is thermodynamically favorable at elevated temperature. Considering heat release from the reverse reaction (ΔH = −23.4 kcal mol−1), the energy storage efficiency was computed to be ca. 5.5% with respect to the IR component in concentrated solar radiation. Solar energy was further utilized for preparation of a model 2,5-norbornadiene derivative (75% isolated yield) through the cycloaddition reaction of Cp with 4-phenylbut-3-yn-2-one at 150–185 °C. The norbornadiene–quadricyclane system has been proposed for solar energy storage, and its solar assisted synthesis would help reduce its carbon footprint over its life cycle. Norbornadiene synthesis using solar energy may also be of interest for greener processing of fuels derived from this compound. Cookson's cage ketone, which too has been proposed as an energy storage medium, was additionally synthesized from the Diels–Alder adduct of Cp and p-benzoquinone employing concentrated solar photo-thermochemical conditions. The reaction proceeded rapidly (15 min) and gave the desired product in 96% isolated yield. Besides the above applications, Cp is an important synthon in the preparation of fine chemicals.

Pauson-Khand reaction of internal dissymmetric trifluoromethyl alkynes. Influence of the alkene on the regioselectivity.

Abstract: The scope of the Pauson-Khand reaction (PKR) of internal trifluoromethyl alkynes, previously described with norbornadiene, is expanded to norbornene and ethylene. A thorough structural analysis of the resulting PK adducts has been carried out to unveil that α-trifluoromethylcyclopentenones are preferred in all cases, independently of the electronic properties of the alkyne. The regioselectivity observed with norbornadiene and ethylene is higher than in the case of norbornene.

The mechanism of inhibited oxidation of norbornene series bicycloolefins

Abstract: The kinetics of oxidation (323 K) of bicycloolefins from the norbornene series: norbornene, vinylnorbornene, ethylidenenorbornene, and norbornadiene, inhibited by phenols (PhOH), aromatic amines (AmH), transition metal compounds (Men), or stable nitroxyl radicals of the piperidine series (>NO·), in chlorobenzene solutions have been studied. It has been found that the phenols are single-action inhibitors, whereas the amines, the transition metals, and the nitroxyl radicals repeatedly terminate oxidation chains. The results are explained in terms of phenomenology of the bicycloolefin oxidation process associated with the fact that peroxide radicals attack different reaction centers (π- and α-CH bonds), thereby resulting in the formation of different types of chain carrier radicals: low-molecular-weight hydroperoxide and polyperoxide radicals.

Electronic vs. Steric Hindrance Effects in Amine Ligands to Ru-Based Initiators for ROMP

Abstract: [RuCl2(PPh3)2(amine)x]-type complexes, with NH2Ph (1; x = 2), NH2Bz (2; x = 2) and NHBuPh (3; x = 1) in the presence of ethyldiazoacetate (EDA), were investigated for ring opening metathesis polymerization (ROMP) of norbornene (NBE), norbornadiene (NBD) and dicyclopentadiene (DCPD). Quantitative yields of polyNBE were obtained at 50 °C for 30 min with 1 and for 5 min with 2, whereas this occurred at 25 °C for 5 min with 3. Polydispersity index (PDI) values ranged from 3.5 to 1.6 (M w = 10 4 -10 5 g mol -1 ). Complex 3 was active for ROMP of NBD and DCPD, as well as for copolymerizations of NBE with either NBD or DCPD. The high σ-donor character of NH2Bz favored the reactivity of the six-coordinated complex 2, contrary to complex 1. The large cone angle of NHBuPh defined the fivecoordination in 3 and the best reactivity for ROMP, in spite of the low σ-donor character as in NH2Ph.

Preparation method of rhodium catalyst by using 2,5-norbornadiene (nbd) and 2-aminonicotinic acid as ligands

Abstract: The invention discloses a preparation method of a rhodium catalyst by using 2,5-norbornadiene (nbd) and 2-aminonicotinic acid as ligands. The preparation method comprises the following steps: taking 26 mg of 2-aminonicotinic acid and 40 mg of potassium hydroxide into a reagent bottle, adding 1.0-2.0 mL of deionized water, and stirring for dissolving; taking 45 mg-55mg of Rh Cl3.3H2O in an inclined two-port flask, injecting 3.0 mL of alcohol and 1.0 mL of a mixed solvent in the presence of a nitrogen gas, and stirring until dissolving completely; adding 0.10 mL-0.20 mL of 2,5-norbornadiene (nbd), stirring for 30 minutes, then heating to 60 DEG C, refluxing, and stirring until liquor is yellow; when 3 hours later, placing under the room temperature and stirring. The novel rhodium complex catalyst obtained by the preparation method disclosed by the invention can be used for further improving the polymerization conversion rate and stereoselectivity while catalyzing substituted acetylene to polymerize.

Method for producing ester compound and palladium catalyst used in method for producing ester compound

Abstract: A method for producing an ester compound, wherein an ester compound is obtained by reacting a compound having at least one cyclic structure, namely a norbornene ring and/or a norbornadiene ring, with an alcohol and carbon monoxide with use of a palladium catalyst and an oxidant so as to introduce an ester group to a carbon atom that constitutes a double bond in the cyclic structure. This method for producing an ester compound is characterized in that the palladium catalyst contains palladium acetate having a nitrite ligand represented by general formula (1) in an amount of 10% by mole or more in terms of metal. Pd3(CH3COO)5(NO2) (1).

Composite catalyst used in preparing quadricyclane through photocatalytic isomerization of norbornadiene and preparation method thereof

Abstract: Disclosed is a composite catalyst used in preparing quadricyclane through photocatalytic isomerization of norbornadiene, the composite catalyst comprising: a solid photocatalyst selected from TiO2, Ti-MCM-41, Ti-SBA-15, ZnO, WO3, Ta2O5 or SrTiO3; an organic photosensitizer loaded on the surface or pores of the solid photocatalyst, the organic photosensitizer being selected from benzophenone, acetophenone, Michler's ketone, tetraethyl Michler's ketone, and diethyl Michler's ketone, the organic photosensitizer accounting for 0.5%-20% of the solid photocatalyst by weight percentage. The catalyst can catalyze a target reaction without the use of a solvent, with a high yield of target product quadricyclane, and the catalyst has stable activity and can be used repeatedly. Also disclosed is a composite catalyst preparation method.

Synthesis of Benzo-ortho-thiazines S-Oxides by Diels—Alder Reaction of N-Sulfinylanilines with Norbornadiene.

Abstract: From substituted N-sulfinylanilines acting as dienes in the Diels-Alder reaction with norbornadiene S-oxides of benzo-ortho-thiazines were obtained, which were oxidized into the corresponding S,S-dioxides belonging to the class of hybrid thiazinesulfonamide compounds.

Method for producing ester compound

Abstract: A method for producing an ester compound including reacting a compound having at least one cyclic structure of a norbornene ring and a norbornadiene ring with an alcohol and carbon monoxide by using a palladium catalyst and an oxidizing agent, to thereby introduce ester groups to carbon atoms forming a double bond in the cyclic structure and obtain the ester compound, wherein the palladium catalyst comprises a palladium complex having a bipyridyl as a ligand

Ester compound production method

Abstract: An ester compound production method, wherein an ester compound is obtained by reacting a compound which has at least one ring structure, namely a norbornene ring or a norbornadiene ring, with an alcohol and carbon monoxide with use of a palladium catalyst and oxidizing agent so as to introduce an ester group to a carbon that forms a double bond in the aforementioned ring structure. In this ester compound production method, the palladium catalyst comprises a palladium complex having bipyridyl as a ligand.

Composite catalyst for the photocatalytic isomerisation of norbornadiene to prepare quadricyclane and process for making the catalyst

Abstract: The present invention discloses a composite catalyst for the photocatalytic isomerisation of norbornadiene to prepare quadricyclane, comprising: a solid photocatalyst, selected from the group consisting of TiO 2 , Ti-MCM-41, Ti-SBA-15, ZnO, WO 3 , Ta 2 O 5 or SrTiO 3 ; and an organic photo-sensitizer loaded on the surface or in the channel of said solid photocatalyst, selected from benzophenone, acetophenone, Michler's Ketone, tetraethyl Michler's Ketone, and diethyl Michler's Ketone, where the organic photo-sensitizer is present in the solid photocatalyst in an amount of 0.5% to 20% by weight. The catalyst of the invention can catalyze a target reaction under the condition that no solvent is used, and the yield of the target product quadricyclane is higher. Furthermore, the catalyst of the invention has a stable activity, and it can be recycled. The invention further discloses a process for preparing the composite catalyst.

Bromosubstituted Norbornadienes and Their Reversible Photolytic Transformation to Quadricyclanes

Abstract: Two new model systems for use within the rapidly developing ultrafast time resolved x-ray scattering techniques have been prepared. Their photoisomerisation from norbornadiene to quadricyclane was found to be a suitable reaction to follow. Simulations of scattering patterns (not included in this report) showed that if heavy atoms are included in these molecular structures, then the transformation can be followed by transient x-ray scattering techniques. Two new bromosubstituted norbornadienes were synthesised and characterised. Absorption spectroscopy showed that the norbornadienes are converted quantitatively to quadricyclanes under UV irradiation. NMR studies showed that the process was fully reversible and that the norbornadienes could be completely recovered even without addition of catalysts. Furthermore, it was shown that the formation of quadricyclane from norbornadiene was unaffected by triplet sensitizers. The two new model systems synthesised thus are strong candidates for use in time resolved x-ray scattering studies both in gas and condensed phases.