Showing papers on "Norbornadiene published in 2010"
TL;DR: In this paper, the photoreactivity is correlated with the surface lattice oxygen, and a mechanism is proposed to explain the photoisomerization and role of Fe dopant.
Abstract: Metal(V, Fe, Ce, Cu, Cr)-doped TiO2 were synthesized for the photoisomerization of norbornadiene. Characterizations indicate that V and Fe are located in the substitutional sites of TiO2, Ce ions dispersed in the interstitial sites, while Cr and Cu aggregated on the surface. The order of activity is Fe−TiO2 > V−TiO2 > Cr−TiO2 > Ce−TiO2 > TiO2 > Cu−TiO2, suggesting the local structure and type of dopant are crucial. Materials with various V and Fe content were further studied. Fe ions are well dispersed in TiO2 lattice even at high metal content, whereas many separated V2O5 phases are formed. The activity of V−TiO2 changes with V content and the optimal Ti/V ratio is 15, but the activity of Fe−TiO2 is independent of the metal content. Attributed to the high dispersion, Fe−TiO2 is much more active than V−TiO2. The photoreactivity is correlated with the surface lattice oxygen, and a mechanism is proposed to explain the photoisomerization and role of Fe dopant.
95 citations
TL;DR: In this article, a poly(phenylacetylene) with rationally designed urea groups was demonstrated to be a superior anion receptor possessing both a colorimetric response ability and a positive homotropic allosteric binding mode.
Abstract: Poly(phenylacetylene) with rationally designed urea groups was demonstrated to be a superior anion receptor possessing both a colorimetric response ability and a positive homotropic allosteric binding mode. The target polymer, poly(phenylacetylene) with [bis(trifluoromethyl)phenyl]urea pendants (poly-1), was synthesized by the stereoselective polymerization with Rh(nbd)BPh4 (nbd = norbornadiene) in high yield. The anion sensing ability of poly-1 was evaluated using the tetra-n-butylammonium (TBA) salts of a series of anions in THF. Upon the addition of anions such as CH3CO2−, C6H5CO2−, F−, Cl−, Br−, NO3−, N3−, and HSO4−, the yellow color of the THF solution of poly-1 immediately turned to a different color depending on the types of anions, indicating the anion recognition capability of poly-1. The 1H NMR titrations of poly-1 by using increasing amounts of CH3CO2− revealed that the colorimetric response of poly-1 was considered to be the direct consequence of the hydrogen-bonding complex formation between ...
68 citations
TL;DR: In this article, it was shown that the Xantphos and POP' ligands are not effective catalysts for the catalyacylation reaction between methyl acrylate and HCOCH(2)CH( 2)SMe at 22 degrees C.
60 citations
TL;DR: In this paper, the photoisomerization of norbornadiene using M-Ti-MCM-41 (M = V, Fe and Cr) has been studied to develop an alternative for solar energy accumulation and high energy aerospace fuel synthesis.
Abstract: The photoisomerization of norbornadiene using M–Ti–MCM-41 (M = V, Fe and Cr) has been studied to develop an alternative for solar energy accumulation and high energy aerospace fuel synthesis. The photocatalysts were prepared via hydrothermal method and characterized by EDX, XRD, N 2 adsorption–desorption, TEM, UV–vis, XPS and IR. With the same Si/M ratio in starting materials, the final concentration of V in the photocatalyst is significantly lower than that of Fe and Cr. V 5+ and Fe 3+ ions are highly dispersed in Si–O framework with tetrahedral coordination when the metal content is low, and the ordered structure is well retained. However, some species in higher coordination and polymerized environments present with increasing metal content, and the ordered structure becomes to collapse. Cr ions are difficult to get into the framework with various species like extraframework Cr 6+ and bulk Cr 2 O 3 formed, also the ordered structure is greatly destroyed. Under UV irradiation, the transition metal ions can improve the photoisomerization activity, with the order of V > Fe > Cr. The activities of V– and Fe–Ti–MCM-41 rise with the increase of Si/M ratio, whereas the performance of Cr–Ti–MCM-41 is irregular. The photocatalysts do not exhibit any activity under visible light, regardless of their absorption in visible-light region. The activity is closely related to the extent of dispersion and local structure of metal ions, about which an indirect excitation process of Ti–O species is suggested.
55 citations
TL;DR: It is shown that the distannyne undergoes reversible complexation with two molecules of either ethylene or norbornadiene, processes that are considered symmetry-forbidden for alkynes but are enabled by the higher reactivity caused by the strained geometry in the heavier analogues.
Abstract: The syntheses of stable heavier group 14 element alkyne analogues have attracted considerable attention in the last decade. Reactivity studies on these molecules have afforded insights into the nature of the E E triple bonds (E= group 14 element), and have supported the existence of a multiplicity of resonance forms, including those with singlet diradical character. Recently we have shown that the distannyne [Ar’SnSnAr’] (1) (Ar’=C6H3-2,6-(C6H3-2,6iPr2)2) undergoes reversible complexation with two molecules of either ethylene or norbornadiene [Eq. (1)], processes that are considered symmetry-forbidden for alkynes but are enabled by the higher reactivity caused by the strained geometry in the heavier analogues.
53 citations
39 citations
TL;DR: In this article, polynorbornadiene and polynorbornene were synthesized via ring opening metathesis polymerization (ROMP) with [RuCl 2 (PPh 3 ) 2 (amine)] as catalyst precursors, amine=piperidine ( 1 ) or perhydroazepine ( 2 ) in the presence of 5μL of EDA.
Abstract: Polynorbornadiene and polynorbornene were synthesized via ring opening metathesis polymerization (ROMP) with [RuCl 2 (PPh 3 ) 2 (amine)] as catalyst precursors, amine = piperidine ( 1 ) or perhydroazepine ( 2 ) in the presence of 5 μL of ethyl diazoacetate (EDA) ([monomer]/[Ru] = 5000; 40 °C with 1 ; 25 °C with 2 ). The effects of the solvent volume (2–8 mL of CHCl 3 ), reaction time (5–120 min) and atmosphere type (argon and air) on the yields were investigated to observe the behavior of the two different precursors. Quantitative yields were obtained for 60 or 120 min regardless of the starting volumes, either in argon or air, with both Ru species. However, low yields were obtained for short times (5–30 min) when the reactions are performed with large volumes (6–8 mL). In argon, the yields were larger with 2 , associated to a faster propagation reaction controlled by the Ru active species. In air, the yields were larger with 1 , associated to a higher resistance to O 2 of the starting and propagating Ru species. The different activities between 1 and 2 are discussed considering the steric hindrance and electronic characteristics of the amines such as ancillary ligands and their arrangements with PPh 3 and Cl − ions in the metal centers.
37 citations
TL;DR: In this article, the reactivity of RuCl2(PPh3)2(3,5-Me2piperidine) complex 1, was investigated for ring opening metathesis polymerization (ROMP) of NBE and norbornadiene (NBD) in the presence of EDA in CHCl3.
Abstract: The reactivity of the new complex [RuCl2(PPh3)2(3,5-Me2piperidine)], complex 1, was investigated for ring opening metathesis polymerization (ROMP) of norbornene (NBE) and norbornadiene (NBD) in the presence of ethyl diazoacetate (EDA) in CHCl3. The aim is to observe the combination of PPh3 and an amine as ancillary ligands concerning the steric hindrance and the electronic perturbation in the properties of the N-bound site when replacing the amines. Thus, the results with 1 were compared to the results obtained when the amine is piperidine (complex 2). Reaction with 1 provides 70% yield of isolated polyNBE (Mn = 8.3 × 104 g/mol; PDI = 2.03), whereas 2 provides quantitative reaction (Mn = 1.2 × 105 g/mol; PDI = 1.90) with [NBE]/[Ru] = 5000, [EDA]/[Ru] = 48 and 1.1 μmol of Ru for 5 min at 25 °C. The resulting polymers showed c.a. 62% of trans-polyNBE, determined by 1H NMR, and Tg = 32 °C, determined by DSC and DMTA. For ROMP of NBD, 1 showed quantitative yield with PDI = 2.62 when [NBD]/[Ru] = 5000 for 20 min at 25 °C, whereas the reaction with 2 reached 55% with PDI = 2.16 in the same conditions. It is concluded that the presence of the two methyl groups in the piperidine ring provides an increase in the induction period to produce the Ru-carbene species justifying better polyNBE results with 2, and a greater amine ⟶ σ Ru ⟶ π monomer synergism which contributed to the best activation of less tensioned olefin as NBD.
32 citations
TL;DR: The nature of substrate activation, and initial bond breaking/making steps, and the dependence of initial rate (k) with diene ligand is in the order COD > NBD > CHD; which corresponds well with the order of hardness of the respective Ag(I) complexes.
Abstract: Silver(I) complex [Ag(diene)2]+Y− (where diene = cyclooctadiene, norbornadiene, and 1,3-cyclohexadiene; Y− = PF6−, BF4−) efficiently catalyzes the arylation of N-tosylaziridines with arenes and heteroarenes under ambient condition to provide the corresponding β-aryl amine derivatives with excellent regioselectivity. To understand the nature of substrate activation, and initial bond breaking/making steps, the following studies were conducted with the help of in situ NMR (1H, 31P, 109Ag) and ESI-MS probe: (I) evaluation of Hammett reaction constant (ρ); (II) correlation of initial rate (k) versus cone angle (θ) of ligand L for reactions mediated by [Ag(COD)2]PF6/L (where L is a phosphine or a phosphite ligand); (III) identification of silver−arene intermediates in solution; and (IV) correlation of initial rate (k) with ΔHOMO−LUMO of [Ag(diene)2]PF6 obtained from preliminary DFT studies. Study I led to a ρ-value of −0.586, indicating that the extent of electrophilic perturbation is considerably less than a t...
29 citations
TL;DR: In this paper, the tetradentate allphosphorus ligands 1−3 were characterized and shown to have high-yielding synthesis and detailed characterization of two well-defined, linkage isomeric tripodal, tetraddate all-phosphorous ligands.
Abstract: The high-yielding synthesis and detailed characterization of two well-defined, linkage isomeric tripodal, tetradentate all-phosphorus ligands 1−3 is described. Coordination to CuI resulted in formation of complexes 4−6, for which the molecular structures indicate overall tridentate coordination to the copper atom in the solid state, with one dangling peripheral phosphine. The solution studies suggest fast exchange between the three phosphine side-arms. For these new CuI complexes, preliminary catalytic activity in the cyclopropanation of styrene with ethyldiazoacetate (EDA) is disclosed. The anticipated well-defined tetradentate coordination in a C3-symmetric fashion was achieved with RhI and IrI, leading to the overall five-coordinated complexes 7−12. Complex 11 has the norbornadiene (nbd) ligand coordinated in an unprecedented monodentate 2,3-η2 mode to Rh. Furthermore, unexpected but very interesting redox-chemistry and reactivity was displayed by the Rh(Cl)-complexes 7 and 8. Oxidation resulted in the...
25 citations
TL;DR: The synthesis and characterisation of a number of group nine complexes containing the recently reported ligand, diphenyl-2-(3-methyl)indolylphosphine, were investigated for their activity in the catalytic transfer hydrogenation of ketones and found to be moderately active catalysts.
Abstract: The synthesis and characterisation of a number of group nine complexes containing the recently reported ligand, diphenyl-2-(3-methyl)indolylphosphine, is presented herein. The complexes [RhCl(COD){PPh2(C9H8N)}] (1), [IrCl(COD){PPh2(C9H8N)}] (2), [RhCl(NBD){PPh2(C9H8N)}] (3) and [Rh(COD)(MeCN){PPh2(C9H8N)}]BF4 (4) (where COD = 1,5-cyclooctadiene, NBD = 2,5- norbornadiene) have been structurally characterised by X-ray crystallography. The complex [Rh2(COD)2{N(Me)C(H)Ph)}{PPh2(C9H8N)}][BF4]2 (8) was also isolated and structurally characterised. Complex 8 contains a ‘[Rh(COD)]’ fragment coordinated to the aromatic ring of the indolyl group, providing the first example of a η6 coordination mode for this ligand. The synthesised complexes were investigated for their activity in the catalytic transfer hydrogenation of ketones and found to be moderately active catalysts.
TL;DR: In this article, the 1,3-dipolar cycloaddition reactions of nitrile sulfides, generated by microwave-assisted decarboxylation of 1, 3, 4-oxathiazol-2-ones, have been investigated.
TL;DR: Stoichiometric and catalytic intermolecular Pauson-Khand reactions of dissymmetric fluorinated alkynes were performed, affording regioselectively α-fluorinated cyclopentenones featuring quaternary centers.
TL;DR: The asymmetric C-H functionalization of norbornene and norbornadiene with five-, six-, and seven-membered cyclic enones mediated by the reactive intermediate Co(NO)(2)] is reported.
Abstract: The asymmetric C-H functionalization of norbornene and norbornadiene with five-, six-, and seven-membered cyclic enones mediated by the reactive intermediate [{η(5)-((t)BuMe(2)Si)C(5)H(4)}Co(NO)(2)] is reported. A novel base mixture derived from enantiopure ammonium salts and NaHMDS was used as a source of chirality, and this enantioselective desymmetrization of C(s) alkenes has been applied to the asymmetric synthesis of C(2)- and C(1)-symmetric diene ligands in high regioselectivity (3.7-20:1 anti/syn), near perfect diastereoselectivity (>99:1 dr), and high enantioselectivity (90-96% ee).
TL;DR: In this paper, the 31P NMR spectra prove that a true migration pathway is the mechanism for this reaction, which is the same mechanism used in the present paper, and they also show that the migration pathway can be used for the insertion of carbon monoxide and norbornadiene.
Abstract: Methylpalladium complexes containing phosphine-phosphinite bidentate ligands 1-3 undergo stepwise insertions of carbon monoxide and norbornadiene. The 31P NMR spectra prove that a true migration pathway is the mechanism for this reaction.
TL;DR: In this paper, the title compound was prepared by condensing a bis(silole) 1 with benzyne, and X-ray structures for the anthracene and DMA adducts were reported.
Abstract: The title compound (2) was prepared by condensing a bis(silole) 1 with benzyne. Thermolysis of 2 in the presence of anthracene, 9,10-dimethylanthracene (DMA), 2,3-dimethylbutadiene, and two acetylenes is described in detail. X-ray structures for the anthracene and DMA adducts are reported.
TL;DR: Radical transannular cyclizations of the nonconjugated dienes, such as 3,7-dimethylenebicyclo[3.3.1]nonane and norbornadiene with SF 5 Cl upon UV-irradiation led to the corresponding SF 5 -substituted 3, 7-noradamantane and nortricyclanes with high yields as discussed by the authors.
TL;DR: In this article, a new species, a five-coordinated rhodium dinorbornadiene chloride (RhN2Cl), was found in the NMR spectra.
Abstract: NMR spectra of solutions containing norbornadiene (N) and μ-dichloro dirhodium dinorbornadiene (Rh2N2Cl2) at low temperatures (< − 40°C) show the presence of a new species, a five-coordinated rhodium dinorbornadiene chloride (RhN2Cl). It is formed according to
Rh2N2Cl2 + 2 N ⇌ 2 RhN2Cl.
At higher temperatures (−40° to + 100°C) line broadening is observed, indicating the occurrence of rapid exchange processes. From the data the following mechanism is deduced: a slow reaction (by one or two steps) of the dimeric complex with one mole of N
Rh2N2Cl2 + N ⇌ RhN2Cl + RhNCl,
and a subsequent fast reaction yielding a second mole of RhN2Cl
RhNCl + N ⇌ RhN2Cl.
TL;DR: In this paper, the crystal and molecular structure of dicarbonyltetramethyl(perfluorohexyl)cyclopentadienyl rhodium(I) complex was determined by X-ray diffraction.
TL;DR: In this paper, the rhodium/olefin-catalyzed reaction of arylboronic acids with an α-acetamido acrylic ester with a chiral norbornadiene ligand was studied.
Abstract: In this paper we present our results concerning the rhodium/olefin-catalyzed reaction of arylboronic acids with an α-acetamido acrylic ester. With a chiral norbornadiene ligand rather low enantioselectivities (up to 21% ee) were obtained. Besides the expected conjugate adduct, we also observed the formation of a significant amount of Mizoroki–Heck-type product. The ratio of the conjugate adduct/Mizoroki–Heck product could be adjusted by a proper choice of the olefin ligand.
TL;DR: In this article, a series of acridinones and benzo-fused acridins have been used for the first time as efficient photosensitizers for the norbornadiene-quadricyclane isomerization by near UV and visible iradiation.
Abstract: In this study, a series of acridinones and benzo-fused acridinones have been used for the first time as efficient photosensitizers for the norbornadiene-quadricyclane isomerization by near UV and visible iradiation. Their triplet energies (240-280 kJ · Mol-1) are well below the value of 290 kJ · Mol-1 which is generally assumed for norbornadiene. A mechanism is postulated involving an exciplex between sensitizer and norbornadiene. Limiting quantum yields of 0.5 and higher have been determined for this valence isomerization extrapolated to infinite norbornadiene concentration. Exciplex formation is supported by measurements of the rate of constant k2 for quenching of excited sensitizer by norbornadiene, yielding values which are much smaller than the diffusion-controlled quenching constant.
TL;DR: The results indicate that the monomeric metal center has the ability to bind with four double bonds of two NBD molecules with a syn spatial geometry to form a penta‐coordinated complex.
Abstract: We investigated the transition metal-catalyzed reaction mechanisms of NBD dimerization to Binor-S using cationic CoI, RhI, and IrI catalysts, using mPW1PW91, mPW1K, and B3LYP density functional methods. Our results indicate that the monomeric metal center has the ability to bind with four double bonds of two NBD molecules with a syn spatial geometry to form a penta-coordinated complex. We designed three possible pathways, but found two of them blocked. The favored pathway involves three steps from the reactant precursor to the product precursor: the first step is the formation of a single bond to connect two NBD units, the second is the alkene insertion leading to the formation of the three-membered ring structure, and the final step is the formation of the final product precursor. Orbital analysis showed metal…CC σ agostic interaction in the product precursor, which is in agreement with the previous experimental findings. In addition, we found that the solvent and counter-ions had significant effects on the dimerization reactions. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010
TL;DR: In this paper, a photolysis reaction was carried out at room temperature in n -heptane (20 cm 3 ) with continued photolytic (2h) at Mo(CO) 6 : R 3 SnH:nbd = 1:50:50.
TL;DR: In this article, a series of cationic rhodium(I) complexes containing the optically pure bis(sulfoximine) ligand 1,2-bis(S-methyl-S-phenylsulfonimidoyl)benzene, have been synthesized and fully characterized.
TL;DR: Time-resolved spectroscopy measurements indicate that the lifetime of the BP triplet state in BP-(amidinium-carboxylate)-NBD is shortened due to the quenching by the NBD group, and the mechanism for the triplet-triplet energy transfer is proposed to proceed via a "through-bond" electron exchange process.
Abstract: A s upramol ecul ar dyad, BP-(amidinium-carboxylate)-NBD is constructed, in which benzophenone (BP) and norbornadiene (NBD) are connected via an amidinium-carboxylate salt bridge. The photophysical and photochemical properties of the assembled BP-(amidinium-carboxylate)-NBD dyad are examined. The phosphorescence of the BP chromophore is efficiently quenched by the NBD group in BP-(amidinium-carboxylate)-NBD via the salt bridge. Time-resolved spectroscopy measurements indicate that the lifetime of the BP triplet state in BP-(amidinium-carboxylate)-NBD is shortened due to the quenching by the NBD group. Selective excitation of the BP chromophore results in isomerization of the NBD group to quadricyclane (QC). All of these observations suggest that the triplet - triplet energy transfer occurs efficiently in the BP-(amidinium-carboxylate)-NBD salt bridge system. The triplet-triplet energy transfer process proceeds with efficiencies of approximately 0.87, 0.98 and the rate constants 1.8 × 10 3 s -1 , and 1.3 × 10 7 s -1 at 77 K and room temperature, respectively. The mechanism for the triplet-triplet energy transfer is proposed to proceed via a "through-bond" electron exchange process, and the noncovalent bonds amidinium-carboxylate salt bridge can mediate the triplet-triplet energy transfer process effectively for photochemical conversion.
TL;DR: In this article, the cycloadditions of olefins containing an electron-withdrawing substituent to norbornadiene were investigated and the influence of substituents and solvent nature on the 2+2+2]-cycloadduct yield and stereoselectivity was elucidated.
Abstract: The cycloadditions of olefins containing an electron-withdrawing substituent to norbornadiene are reported. The influence of the substituent and solvent nature on the [2+2+2]-cycloadduct yield and stereoselectivity is elucidated. The competitive cycloaddition of pairs of olefins to norbornadiene is discussed. Hypotheses about the structure of key intermediates of the process are considered. The consistent generalized mechanism for the cycloaddition of unsaturated compounds of various classes to norbornadiene is suggested.
TL;DR: In this article, Ru-catalyzed [(2+2)+2] cycloaddition and subsequent transfer hydrogenation were confirmed by X-ray crystal analysis, which provided high diastereoselectivity to generate norbornenes 7−11 in up to 82% yield.
TL;DR: In this article, a diad compound 3β(bicyclo[2,2,1]hepta-2,5-diene-2-methylcarboxylate-3-carboxy)-androst-5-en-17-one (NBD-S-ONE) was synthesized and its photochemistry was examined.
Abstract: A diad compound 3β(bicyclo[2,2,1]hepta-2,5-diene-2-methylcarboxylate-3-carboxy)-an-drost-5-en-17-one (NBD-S-ONE) was synthesized and its photochemistry was examined. Irradiation of NBD-S-ONE in acetonitrile at λ > 300 nm selectively excited the keto chromophore. After intersystem crossing, the triplet energy of the keto group was transferred to the NBD group with 18.6% efficiency via a through-bond mechanism, resulting in the isomerization of the latter group to the quadricyclane group.
TL;DR: The trifluoromethylenaminoketones, with a strained cyclobutene and norbornadiene moieties, were firstly prepared from the corresponding β-halogeno-α,β-unsaturated triflumineto-β-ketones in almost quantitative yields.
TL;DR: In this article, the authors synthesized cyclodextrin derivatives with pendant norbornadiene (CD-NBD), pendant azobenzene, pendant cinnamate, and pendant anthracene.