Showing papers on "Norbornadiene published in 2013"
TL;DR: An efficient, palladium-catalyzed cascade reaction, which leads to formation of annulated xanthones, was devised and serves as a new approach to achieve regioselective control of C–H activation in Pd/norbornene or norbornadiene systems.
Abstract: An efficient, palladium-catalyzed cascade reaction, which leads to formation of annulated xanthones, was devised. The process, which uses readily available 3-iodochromones, aryl iodides and norbornadiene as starting materials, takes place via a tandem Heck reaction/double C–H activation/retro-Diels–Alder pathway. The high chemoselectivity of the process is mechanistically unique and it serves as a new approach to achieve regioselective control of C–H activation in Pd/norbornene or norbornadiene systems. Its broad substrate scope, including heteroaryl coupling partners, enables access to diverse annulated xanthones.
41 citations
TL;DR: In this article, a simple and efficient method for aminocarbonylation of aryl, benzyl, and styryl iodides and bromides using the in situ generated molybdenum tetracarbonyl norbornadiene [Mo(CO)4(nbd)] complex as a suitable source of carbon monoxide.
36 citations
TL;DR: The complexes of various Rh precusors with ferrocenyl chiral ligand (R,S)-Cy2PF-PPh2 were found effective catalysts for the asymmetric hydroalkynylation reaction of norbornadiene derivatives.
36 citations
TL;DR: Employing a series of norbornadiene derivatives as substrates, the effects of various substituents on the Ir-catalyzed asymmetric [2 + 2] cycloaddition reactions with arylacetylenes were studied and it was found that the atom forming the short bridge chain had a great effect on the enantioselectivity of the reaction.
Abstract: Employing a series of norbornadiene derivatives as substrates, the effects of various substituents on the Ir-catalyzed asymmetric [2 + 2] cycloaddition reactions with arylacetylenes were studied. It was found that the atom forming the short bridge chain had a great effect on the enantioselectivity of the reaction. Heteroatoms, such as oxygen and nitrogen, always resulted in excellent enantioselectivity. However, carbon atoms could decrease the enantioselective control ability of the catalyst over the reaction. The groups on the unreacted carbon–carbon double bond were found to have but a little effect on the reaction. Based on the results of the experiments, a mechanism was also hypothesized for the reaction.
33 citations
TL;DR: In this article, the rhodium (Rh) catalysts [nbd-(CH2)4-X}RhR] (1, X = PPh2, R = Cl; 2, X, N Ph2, Cl; 3, X, NPh2 and R = triphenylvinyl; nbd = 2,5-norbornadiene) were synthesized, and their catalytic activities were examined for the polymerization of phenylacetylene and its derivatives.
29 citations
TL;DR: Going chiral!
Abstract: Going chiral! Highly enantioselective catalytic hydrogenations of enol esters 1 by using a Rh catalyst bearing a P-OP ligand are described (see scheme; NBD=norbornadiene). The catalytic system has a broad scope and allows the preparation of a wide range of chiral esters 2 bearing diverse alkyls or a benzyl group with high enantioselectivities. These esters can easily be converted in highly enantioenriched 2-alkanols.
27 citations
TL;DR: The crystal structure of 9a, determined in addition to the solution structure elucidation by multinuclear NMR spectra, confirms the chelate formation and reveals a trigonal environment for the low coordinated phosphorus.
Abstract: Acid-catalyzed cyclocondensations of 2-phosphanylanilines 1 with substituted benzaldehydes or heteroaryl aldehydes open a convenient route to new biaryl-type 1H-1,3-benzazaphosphole hybrid ligands 2a–f with o-phosphanylphenyl, pyridyl, imidazolyl, thienyl or o-methoxyphenyl donor groups (in addition to the σ2P donor) and to bromophenyl substituted benzazaphospholes 2g,h. Excess aldehyde leads to concomitant reductive N-alkylation, as shown by formation of 3h besides 2h. The reactions proceed via dihydrobenzazaphospholes 4, which can be detected under mild conditions. The aromaticity-driven dehydrogenation does not liberate dihydrogen but is accomplished by transfer hydrogenations, mainly by reduction of some of the aldehyde. N-Secondary 2-phosphanylanilines 5 also react with aldehydes to form the corresponding N-substituted benzazaphospholes 6. The formation of (P^P′)M(CO)4-chelate complexes 8a (M = Cr) and 9a,b (M = Mo) was demonstrated by reaction with M(CO)4(norbornadiene). The crystal structure of 9a, determined in addition to the solution structure elucidation by multinuclear NMR spectra, confirms the chelate formation and reveals a trigonal environment for the low coordinated phosphorus, with the P–Mo(0) vector bent out of the benzazaphosphole ring plane by 14.4° (0.57 A), together with axial chirality of the molecules in the racemic crystals by twisting of the benzazaphosphole and phenyl π-planes around the common C(2)–C(21) bond.
27 citations
TL;DR: The regioselectivity of the PKR of a family of trifluoromethylacetylenes was studied, and a new procedure was uncovered, outlined in Scheme 2, to prepare an efficient procedure to remove the trif LU group.
Abstract: The reaction between alkynes (I) and norbornadiene (II) affords the β-substituted Pauson—Khand adducts (III) as single regioisomers and the trifluoromethyl steering group can be easily removed in the presence of DBU and water.
24 citations
TL;DR: The rhodium-catalyzed highly regioselective 1:2 coupling of aldehydes and allenes was investigated and it was shown that the energetically most plausible catalytic cycle is initiated by oxidative coupling of the two allenes, which was found to be the rate-determining step of the overall reaction.
Abstract: The rhodium-catalyzed highly regioselective 1:2 coupling of aldehydes and allenes was investigated by means of density functional theory calculations. Full free energy profiles were calculated, and several possible reaction pathways were evaluated. It is shown that the energetically most plausible catalytic cycle is initiated by oxidative coupling of the two allenes, which was found to be the rate-determining step of the overall reaction. Importantly, Rh–allyl complexes that are able to adopt both η3 and η1 configurations were identified as key intermediates present throughout the catalytic cycle with profound implications for the selectivity of the reaction. The calculations reproduced and rationalized the experimentally observed selectivities and provided an explanation for the remarkable alteration in the product distribution when the catalyst precursor is changed from [RhCl(nbd)]2 (nbd = norbornadiene) to complexes containing noncoordinating counterions ([Rh(cod)2X]; X = OTf, BF4, PF6; cod = 1,5-cyclo...
24 citations
TL;DR: In this paper, a poly(n)-Heptylphenylacetylene (pHepPA) was stereoregularly polymerized in n-hexane at 25 °C using [Rh(nbd)Cl]2 catalyst (nbd: norbornadiene) and NEt3, affording the purple-red poly(R) in 97% yield.
Abstract: p-n-Heptylphenylacetylene (pHepPA) was stereoregularly polymerized in n-hexane at 25 °C using [Rh(nbd)Cl]2 catalyst (nbd: norbornadiene) and NEt3, affording the purple-red Poly(R) in 97% yield. A 80 °C heat treatment transformed Poly(R) to the black Poly(B). The Poly(R) X-ray diffraction (XRD) pattern revealed a hexagonal crystal structure comprising contracted cis-cisoid helices [HexaPoly(R)CC]. The 80 °C heat treatment generated two tetragonal crystals: TetraPoly(B)CC containing contracted cis-cisoid helices and TetraPoly(B)CT containing stretched cis-transoid helices. The helical diameters before and after heat treatment were estimated using XRD and were consistent with molecular mechanics calculations (MMFF94 force field method). When heated at 80 °C in the solid phase, the λmax in the diffuse reflective UV–vis spectra of HexaPoly(R)CC shifted from 482 to 560 nm. Additionally, an endothermic transition occurred in the HexaPoly(R)CC differential scanning calorimetric trace at ∼80 °C. Therefore, these data corroborated the assertion that HexaPoly(R)CC thermally converted to TetraPoly(B)CC and TetraPoly(B)CT. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 5177–5183
21 citations
TL;DR: In this article, the authors describe novel developments in the framework of the studies of sequential palladium-catalyzed reactions, involving palladacycle formation with norbornene or norbornadiene via aromatic C-H activation.
TL;DR: The synthesis of tetracene- and pentacene-annulated norbornadienes, formed through the Diels-Alder reaction of a dehydroacene with cyclopentadiene is reported.
Abstract: The synthesis of tetracene- and pentacene-annulated norbornadienes, formed through the Diels-Alder reaction of a dehydroacene with cyclopentadiene is reported. Ring-opening metathesis polymerization (ROMP) leads to polymers that are investigated with respect to their physical, optical, and electronic properties by gel permeation chromatography (GPC), UV-vis spectroscopy, and cyclic voltammetry. The pentacene-containing polymer P1 is successfully integrated into an organic field-effect transistor (OFET); the tetracene-containing polymer P2 is integrated into an organic light-emitting diode (OLED).
TL;DR: A new approach to the synthesis of 4,5-disubstituted cyclopentenones is described, based on the Pauson-Khand reaction of norbornadiene and N-Boc-propargylamine as an alkyne with a masked leaving group, which can be eliminated at will.
TL;DR: Kinetic data for the C-Cl activation in both the solid-state and solution are reported and the dimeric Rh(III) complex is reported.
Abstract: Addition of H2 to [Rh(iBu2PCH2CH2PiBu2)(NBD)][BArCl4] (NBD = norbornadiene, ArCl = 3,5-Cl2C6H3) in the solid-state results in the rapid formation of zwitterionic [Rh(iBu2PCH2CH2PiBu2){(η6-C6H3Cl2)BArCl3}] by a gas/solid reaction. This undergoes slow C–Cl bond cleavage in the solid-state to ultimately afford the dimeric Rh(III) complex [RhCl(iBu2PCH2CH2PiBu2){C6H3Cl(BArCl3)}]2. This reactivity is mirrored in solution (CH2Cl2). Kinetic data for the C–Cl activation in both the solid-state and solution are reported.
TL;DR: In this article, a ring opening metathesis copolymerization with norbornene (NBE) with NBD (NBD 0.8 : 0.2 ) was performed with [RuCl2(PPh3)2(amine)] complex types as precatalysts.
Abstract: Copolymers from norbornene (NBE) with norbornadiene (NBD) were synthesized via ring opening metathesis copolymerization varying the mole fractions of the comonomers (0.8 : 0.2; 0.6 : 0.4; 0.4 : 0.6; 0.2 : 0.8) for a total monomer quantity of 5000 equivalents/[Ru]. The batch reactions were performed with [RuCl2(PPh3)2(amine)] complex types as precatalysts, where amine is perhydroazepine (1) or piperidine (2), in CHCl3 (2 mL) in the presence of ethyl diazoacetate (5 μL) for different intervals of times (5, 30, 60, and 120 min) at 40°C. The copolymers were characterized by 13C NMR. Quantitative yields of isolated materials were obtained from solutions with NBD : NBE 0.8 : 0.2 mole fraction in the presence of 1, decreasing to 70% for NBD : NBE 0.2 : 0.8 solutions. Concerning 2, the yields were 70% at most. Polymeric materials obtained with 1 were less soluble in CHCl3 than those synthesized with 2. The dependence of the reaction yields and occurrence of crosslinking on the starting NBE : NBD proportion related to reactivity of the complexes 1 and 2 were discussed. A few differences in the amines such as ancillary ligands were sufficient to change the reactivity of the {RuCl2(PPh3)} moiety complex to provide copolymers with different compositions. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
TL;DR: In this article, the density functional theory (DFT) at the PBE level was used to model the mechanism of the cycloaddition of ethyl acrylate to norbornadiene (NBD) catalyzed by Ni0 complexes.
Abstract: The mechanism of the [2+2+2] cycloaddition of ethyl acrylate to norbornadiene (NBD) catalyzed by Ni0 complexes was modeled in terms of the density functional theory (DFT) at the PBE level. The formation of the first C—C bond between the coordinated NBD and ethyl acrylate molecules is the rate-determining step of the process. The low stereoselectivity of the reaction is due to the close matching of the activation barriers for the formation of exo- and endo-cycloadducts (25.6 and 24.9 kcal mol−1, respectively).
TL;DR: Rhodium complexes with planar chiral phosphinoferrocenyl thioether ligands [Rh(P,SR)(diene)X] (R = Me, But, Ph, Bn, diene is cyclooctadiene (COD), X = Cl, BF4) catalyze hydrogenation of ketones, imines, and heteroaromatic compounds; in the case of acetophenone, the enantioselectivity reached 60% ee.
Abstract: Rhodium complexes with the planar chiral phosphinoferrocenyl thioether ligands [Rh(P,SR)(diene)X] (R = Me, But, Ph, Bn, diene is cyclooctadiene (COD) or norbornadiene (NBD), X = Cl, BF4) catalyze hydrogenation of ketones, imines, and heteroaromatic compounds; in the case of acetophenone, the enantioselectivity reached 60% ee. Similar iridium complexes demonstrate a good activity in the hydrogenation of imines, the maximal enantioselectivity in the case of N-phenyl-N-(1-phenylethylidene)amine was about 40% ee.
TL;DR: Not accessible to established characterization methods, the oily, extremely reactive unpurified mixture of 3 with scrambled ligands was characterized by mass spectrometry using liquid injection field desorption ionization (LIFDI).
TL;DR: In this article, the conformational changes in 4 are still fast at 223 K and slow at room temperature and 223 K, respectively, whereas 3 and 4 undergo intramolecular exchanges.
Abstract: [MCl(L2)]2 (M = Ir, L2 = 1,5-cyclooctadiene; M = Rh, L2 = norbornadiene) reacts with [2-(1,3-dioxolane-2-yl)phenyl]diphenylphosphane (1) to afford [MCl(L2)(P~O)] (M = Ir, 2; M = Rh, 3), in which the ligand is P-monodentate. Complex 3 reacts with AgClO4 to give [Rh(Nbd)(PO)]ClO4 (4), in which the ligand is P,O-bidentate. Complex 2 is static at room temp., whereas 3 and 4 undergo intramolecular exchanges, which are fast at room temperature and slow at 223 K. The conformational changes in 4 are still fast at 223 K. Complexes 2–4 react with CO to afford trans-[MCl(CO)(P~O)2] (M = Ir, 5; M = Rh, 6) or trans-[Rh(CO)2(P~O)2]ClO4 (7). Cyclooctadiene complexes react with PPh2(o-C6H4CHO) to afford [MClH(PPh2(o-C6H4CO))(PO] (M = Ir, 8; M = Rh, 9), in which 1 is chelating. Complex 8 contains a single diastereomer, is static in the 303–213 K range and reacts with CO to form [IrClH(PPh2(o-C6H4CO))(P~O)(CO)] (10). Complex 9 contains two diastereomers 9a/9b in a 95:5 ratio that undergo interconversion, which is slow at low temperature, and reacts with CO to undergo reductive elimination of aldehyde, cleavage of the Rh–O bond and scrambling of phosphanes. A mixture of trans-[RhCl(CO)(κ1-PPh2(o-C6H4CHO))(P~O)] (11), 6 and trans-[RhCl(CO)(κ1-PPh2(o-C6H4CHO))2] is formed. Bubbling of nitrogen transforms 11 back into 9. Compound 2 reacts with hydrogen to give the fluxional [IrCl(H)2(P~O)(PO)] (12) with trans P atoms and cis H atoms, which attains coalescence at 203 K. Complex 12 reacts with mono- or bidentate ligands to afford static [IrCl(H)2(P~O)2L] (L = CO, 13; py, 14; nPrNH2, 15) or [Ir(H)2(P~O)2(en)]BPh4 (16, en = ethylenediamine). Abstraction of halide from 12 affords [Ir(H)2(PO)2]BPh4 (17), which is fluxional owing to interconversion between only two of the possible four diastereomers, for which ΔH‡ = 54.7 ± 0.7 kJ mol–1 and ΔS‡ = 4.7 ± 0.2 J K–1 mol–1. The X-ray structures of 8, 15 and 16 are also reported.
TL;DR: In this paper, the rate-determining step in the cyclodimerization process is reductive elimination of the metallacycle whose decomposition yields norbornadiene dimer.
Abstract: [2+2]-Cyclodimerization of norbornadiene to pentacyclic products with exo-trans(cis)-exo structure in the presence of model catalytically active η4-norbornadiene nickel hydride complex was simulated at the DFT/PBE level of theory. According to the calculations, the rate-determining step in the cyclodimerization process is reductive elimination of the metallacycle whose decomposition yields norbornadiene dimer. The formation of cis-dimer is unfavorable for both kinetic and thermodynamic reasons.
TL;DR: The 3,6-di(2-pyridyl)-pyrinonorbornadiene cycloadducts were used to produce pyridazines (diene-protected alkenes) as discussed by the authors.
Abstract: Norbornadiene cycloadducts reacted with 3,6-di(2-pyridyl)-s-tetrazine to produce pyridazines (diene-protected alkenes), following dehydrogenation (by DDQ) of the intermediate dihydropyridazines. The title 3,6-di(2-pyridyl)-pyridazinonorbornadiene was produced under flash vacuum pyrolysis conditions by ejection of anthracene (590 °C), isobenzofuran (630 °C) or isoindole (580 °C) from the corresponding pyridazines, establishing the following dienofugacity order: isoindole > anthracene > isobenzofuran. Calculations of the respective retro-Diels–alder activation energies at the B3LYP/6-31G* level of theory correctly predicted the experimentally found isobenzofuran > anthracene > isoindole order. Cavity bis-3,6-di(2-pyridyl)-pyridazine (dppn) and chevron-shaped bis-dppn ligands were prepared from the title compound by coupling at the norbornene π-bond.
TL;DR: In this paper, the influence of the bisphosphine structure on the regio-and stereoselectivity of the reaction as well as on the yields of reaction products was investigated.
Abstract: [2+2+2] Cycloaddition of electron-deficient olefins to norbornadiene in the presence of nickel bisphosphine catalysts was studied. The influence of the bisphosphine structure on the regio- and stereoselectivity of the reaction as well as on the yields of the reaction products was investigated. New evidence for the influence of chiral bisphosphine ligands on the enantioselectivity of the reaction was obtained.
TL;DR: In this paper, cyclodimerization of norbornadiene yielding pentacyclic products of exo-trans(cis)endo-structure in the presence of the model catalytically active complex Ni(H)(η4-NBD) has been studied using the DFT/PBE method.
Abstract: Cyclodimerization of norbornadiene (NBD) yielding pentacyclic products of exo-trans(cis)endo-structure in the presence of the model catalytically active complex Ni(H)(η4-NBD) has been studied using the DFT/PBE method. The rate-limiting reaction step is the reductive elimination of the metallacycle, the decomposition of the latter yields the norbornadiene dimer.
TL;DR: In this article, 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.
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.
TL;DR: In this paper, a qualitative explanation of catalytic behavior of Mn-phthalocyanine and Co-tetraphenylporphyrin is obtained from the analysis of the spectra of local many electron states of free catalysts and their complexes with the reactant/product.
Abstract: The theory of catalytic activity of transition-metal compounds is a fascinating problem especially if a comparison of different catalysts is necessary. The isomerization of quadricyclane (QC) to norbornadiene (NB) catalyzed by transition-metal porphyrins is a challenge and incidentally a suitable benchmark for various theories of catalysis. We analyze this process in detail using a valence bond-like scheme adjusted for the description of reaction centers containing transition-metal atoms. A qualitative explanation of contrasting catalytic behavior of Mn-phthalocyanine and Co-tetraphenylporphyrin is obtained from the analysis of the spectra of local many electron states of free catalysts and their complexes with the reactant/product. This picture is supported by the numerical analysis of potential energy profiles for the QC to NB isomerization in the presence of a catalyst performed in the effective Hamiltonian approximation. This exemplary reaction is put in a more general perspective of theories of catalytic activity of transition-metal complexes and in relation with oxygenation reactions. © 2013 Wiley Periodicals, Inc.
TL;DR: The reaction of norbornene (II) and norbornadiene (X) with indoles, thiophenes, furans and pyrroles proceeds with moderate to high enantioselectivities as discussed by the authors.
Abstract: The reaction of norbornene (II) and norbornadiene (X) with indoles, thiophenes, furans and pyrroles proceeds with moderate to high enantioselectivities.
TL;DR: In this article, the Yamazaki-Higashi reaction between a pentamethylated NBD dicarboxylic acid and a series of aromatic diamines is used to obtain polyamides with glass transition temperatures ranging from 68 to 124 � C.
Abstract: Photoresponsive polyamides containing main-chain pentamethylated norbornadiene (NBD) moieties are obtained in quantitative yields via the Yamazaki-Higashi reaction between a pentamethylated NBD dicarboxylic acid and a series of aromatic diamines. Chemical structures are confirmed by 1 H and 13 C NMR and weight average molar masses measured by SEC are in the range of 21,500-28,600 g mol 21 with chain dis- persities close to 2. Physical properties are investigated by FTIR, differential scanning calorimetry (DSC), thermogravimet- ric analysis, and viscosimetry. All obtained polyamides are amorphous with glass transition temperatures ranging from 68 to 124 � C. They are soluble at room temperature in common organic solvents and exhibit good thermal stabilities with Td10 values ranging from 175 to 276 � C. The photochemical isomeri- zation of the NBD moiety into quadricyclane (QC) is studied by UV/vis spectroscopy after sunlight irradiation of polymer films. For all polyamides, a first-order kinetic rate is observed for the conversion of NBD to QC. The thermal release of the stored energy associated to the reverse transformation of QC groups into NBD ones is about 90-95 kJ mol 21 as measured by DSC of the irradiated polymer films. V C 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 00, 000-000
TL;DR: In this paper, the effect of alcohol additives on the catalytic, enantioselective aqueous hydrogenation of acetophenone is examined with the newly developed (R,R)-DAMPYPHOS as the ligand and Rh2(norbornadiene)2Cl2 as the catalyst precursor, giving rise to higher conversions and improved enantiomeric excesses (up to 95%) of the formed 1-phenylethanol.
TL;DR: In this paper, the reaction mechanism for the hydrogenation of norbornadiene (nbd) catalysed by bis-norbornadene rhodium(I) [Rh(nbd)+ complex has been studied by means of DFT based methods, in the absence and in the presence of a self-folding octaamide cavitand.
Abstract: The reaction mechanism for the hydrogenation of norbornadiene (nbd) catalysed by bis-norbornadiene rhodium(I) [Rh(nbd)2]+ complex has been studied by means of DFT based methods, in the absence and in the presence of a self-folding octaamide cavitand. Formation of three products, norbornene, nortricyclene and a dimer is discussed. When the metal complex is encapsulated inside the cavitand, the steric crowding prevents formation of the dimer, while in the absence of the cavity, the dimer is the major product. Although energy differences between the studied reaction pathways are small, the present study explains the changes in regioselectivity when the hydrogenation reaction is carried out in a confined space.