Showing papers on "Norbornadiene published in 1996"
TL;DR: In this paper, real-time studies of the retro-Diels-Alder reactions of norbornene (NB) and norbornadiene (NBD), products of the cycloaddition of cyclopentadiene with ethylene and acetylene, respectively, are presented.
Abstract: In this communication, we present our first femtosecond (fs), real-time studies of the retro-Diels-Alder reactions of norbornene (NB) and norbornadiene (NBD), products of the cycloaddition of cyclopentadiene with ethylene and acetylene, respectively. The reaction path, together with transition state (TS) structures, is displayed in Figure 1 (bottom). The experiments were designed with the following considerations in mind. First, the reactions were studied in a molecular beam in order to isolate the elementary processes, free of solvent perturbations. Second, we examined the dynamics of the reaction from a well-defined initial geometry, a precursor of Diels-Alder products.
101 citations
TL;DR: In this article, the coordination chemistry of 2,2-dipyridyl diselenide (PySeSePy) (2) (C10H8N2Se2) has been investigated and its crystal structure has been determined.
Abstract: The coordination chemistry of 2,2‘-dipyridyl diselenide (PySeSePy) (2) (C10H8N2Se2) has been investigated and its crystal structure has been determined (monoclinic, P21/c, a = 10.129(2) A, b = 5.7332(12) A, c = 19.173(3) A, β = 101.493(8)°, Z = 4). In metal complexes the ligand was found to coordinate in three different modes, as also confirmed by X-ray structure determination. N,N‘-coordination was found in the zinc complex [Zn(PySeSePy)Cl2] (3) (C10H8Cl2N2Se2Zn, triclinic, P1, a = 7.9430(10) A, b = 8.147(2) A, c = 11.999(2) A, α = 93.685(10)°, β = 107.763(10)°, γ = 115.440(10)°, Z = 2) and Se,Se‘-coordination in the adduct of the ligand with bis(pentafluorophenyl)mercury(II) [PySeSePyHg(C6F5)2] (5) (C10H8F10HgN2Se2, monoclinic, P21/n, a = 7.7325(10) A, b = 5.9974(14) A, c = 25.573, β = 98.037(10)°, Z = 2), which however displays only weak interactions between selenium and mercury. The reaction of the ligand with norbornadiene carbonyl complexes of molybdenum and tungsten leads to reductive cleavage of ...
100 citations
TL;DR: The monoanionic ligand [C6H3(CH2NMe2)2-2,6], a potentially terdentate N,C,N bonding system, has been employed to synthesize a series of new ruthenium(II) complexes as mentioned in this paper.
71 citations
TL;DR: The reaction between W(CH-t-Bu)(O)(PMe3)2Cl2 and 2 equiv of KO-2,6-Ph2C6H3 yields yellow crystalline syn-W(CH t-Bu) (O)(OAr)2(Pme3) (1a).
57 citations
46 citations
TL;DR: In this article, the bis(pentaammineruthenium(II)) complex of dicyanonorbornadiene has been prepared and characterized, and it exhibits an intervalence transition in the 1000−1600 nm range.
Abstract: The bis(pentaammineruthenium(II)) complex of dicyanonorbornadiene has been prepared and characterized. Its photochemical conversion into a dicyanoquadricyclane complex by irradiation in methanol has been followed by UV−visible spectroscopy, IR spectroscopy, 1H NMR spectroscopy, and cyclic voltammetry. The dicyanonorbornadiene complex exhibits an intervalence transition in the 1000−1600 nm range when oxidized to the ruthenium(II)−ruthenium(III) state. This allows the determination of the effective coupling Vab through the dicyanonorbornadiene ligand, which is found as 0.023 eV. No such band is observed in the case of the dicyanoquadricyclane complex. These results show the possibility to modulate an intramolecular electron transfer process by using a photoisomerizable bridging ligand.
45 citations
TL;DR: The 125 MHz 13 C NMR spectra of the hydrogenated derivatives of ring-opened metathesis polymers (ROMP) of bicydo[2.2.1]hept-2-ene (norbornene) and bicydo-2.5-diene(norbornadiene) prepared using a range of initiators, have been analysed in detail as mentioned in this paper.
Abstract: The 125 MHz 13 C nuclear magnetic resonance (NMR) spectra of the hydrogenated derivatives of ring-opened metathesis polymers (ROMP) of bicydo[2.2.1]hept-2-ene (norbornene) and bicydo[2.2.1]hepta-2,5-diene (norbornadiene) prepared using a range of initiators, have been analysed in detail. The signals due to the methylene carbon atoms in the enchained cyclopentyl rings of these polymers show fine structure which is assigned to m and r ring dyads and mm, mr/rm and rr ring triads, enabling the tacticity of the hydrogenated polymer, and thus of the polyolefin precursor, to be determined for high-cis or high-trans polymers. Novel methods for making high-cis polymers are described and solvent-dependent variations in the stereospecificity of the propagation reaction have been observed.
42 citations
TL;DR: In this article, fluorescent polyphenylene films bearing a norbornadiene substituent were electrosynthesized for the first time, and the photoisomerization kinetics of the pendant NBD group were investigated.
40 citations
36 citations
TL;DR: In this paper, the authors show that the trans coordination of the benzene ring of the indenyl-Rh(CO)2 complex with tricarbonylchromium strongly enhances the rate of substitution of CO's with bidentate olefins, 1,5-cyclooctadiene (COD) and norbornadiene, and the activation parameters suggest an associative reaction pathway assumed to proceed via the intermediacy of a nonisolable low-hapticity species.
32 citations
TL;DR: In this article, various epoxy monomers containing norbornadiene (NBD) moieties were prepared by reactions of potassium salts of NBD derivatives with excess epichlorohydrin using tetrabutylammonium bromide (TBAB) as a phase transfer catalyst.
Abstract: Various epoxy monomers containing norbornadiene (NBD) moieties were prepared by reactions of potassium salts of NBD derivatives with excess epichlorohydrin using tetrabutylammonium bromide (TBAB) as a phase transfer catalyst. The copolymerization of glycidyl (3-phenyl-2,5-norbornadien-2-yl)carboxylate (GPNC) with phthalic anhydride (PAn) proceeded smoothly using TBAB as a catalyst in sulfolane at 100 °C for 24 h to give polyester P-1 containing pendant NBD moieties. Copolymerizations of various epoxy monomers containing certain NBD moieties with carboxylic anhydrides gave the corresponding NBD polyesters in good yields. The photochemical valence isomerizations of the NBD moieties in the polymers were carried out in the film state or in the solution. Rates of the isomerizations of some NBD moieties in the polymers were strongly enhanced by the addition of photosensitizers such as 4-(N,N-dimethylamino)benzophenone (DABP). The Tgs of the polyesters having NBD residues and stored thermal energy in the corresp...
TL;DR: In this paper, a long-distance intramolecular triplet energy transfer was proposed to proceed via a through-bond exchange mechanism, and the efficiency and rate constant were determined to be ca. 22% and 1.5 × 105 s-1, respectively.
Abstract: Bichromophoric compound 3β-((2-(methoxycarbonyl)bicyclo[2.2.1]hepta-2,5-diene-3-yl)carboxy)androst-5-en-17β-yl benzophenone-4-carboxylate (NBD-S-BP) was synthesized, and its photochemistry was examined. The phosphorescence of the benzophenone (BP, donor) chromophore is efficiently quenched by the remote norbornadiene (NBD, acceptor) group. Time-resolved spectroscopic measurements indicate that the lifetime of the triplet state of the BP chromophore is shortened by the NBD group. Selective excitation of the BP chromophore results in isomerization of the NBD group to quadricyclane. All these observations suggest that a long-distance intramolecular triplet energy transfer occurs in the NBD-S-BP molecule. The efficiency and rate constant for this triplet energy transfer were determined to be ca. 22% and 1.5 × 105 s-1, respectively, by steady-state photolysis and laser flash photolysis. This long-distance intramolecular triplet energy transfer is proposed to proceed via a through-bond exchange mechanism.
TL;DR: In this paper, the 351 nm photoelectron spectra of several isomers of C7H7, obtained by deprotonating quadricyclane, norbornadiene, 1,6-heptadiyne, and cycloheptatriene, are reported.
Abstract: The 351 nm photoelectron spectra of several isomers of C7H7-, obtained by deprotonating quadricyclane, norbornadiene, 1,6-heptadiyne, and cycloheptatriene, are reported. Quadricyclane can be deprotonated from either of two distinct sites by amide anion. The electron affinities (EAs) of the two corresponding C7H7• isomers are 0.868(6) and 0.962(6) eV, with one well-resolved vibration observed for each state, at 909(20) and 826(20) cm-1, respectively. Deprotonation of norbornadiene by amide anion leads to formation of one ionic isomer with a binding energy of 1.286(6) eV. Detachment to form an excited state of the neutral is also observed, with a vertical detachment energy (VDE) of 2.8(1) eV. Three vibrational modes are resolved in the ground state region of the spectrum, and one excited state vibration is observed. 1,6-Heptadiyne is deprotonated by hydroxide at two sites, the end carbon (C1) and the third carbon (C3), to produce isomers with binding energies of 3.037(10) and 1.132(6) eV, respectively. One ...
TL;DR: In this article, the geometrical structures of poly(α-ethynylnaphthalene) and WCl 6 catalysts with respect to the CC bond in the main chain were investigated.
TL;DR: In this article, the feasibility of doubly bridged ansa-zirconocenes based on the norbornadiene skeleton was investigated by molecular mechanics analysis on models of catalytic intermediates corresponding to the monomer coordination step as well as on the pseudotransition states relative to the possible monomer insertion reaction.
TL;DR: Columnar polymers of p-methylethynylbenzene (MEB) were synthesized using [Rh(norbornadiene)Cl]2 as a catalyst in alcohol.
Abstract: Columnar polymers of p-methylethynylbenzene (MEB) were synthesized using [Rh(norbornadiene)Cl]2 as a catalyst in alcohol. Polymers having a cis-transoid structure were selectively formed at high yields. The structure and properties of the polymers were analyzed by means of X-ray diffraction and ESR methods. The data showed that the pristine amorphous polymer was converted to a pseudohexagonal columnar one when it was treated with toluene at room temperature. Formation of columnar polymers was also demonstrated by the increase in the linewidth in the ESR spectra of the polymer obtained by the toluene treatment of the pristine amorphous polymer, indicating that a magnetically inhomogeneous line broadening mechanism operates among the radical spins which are heterogeneously distributed in the columnar phase.
TL;DR: In this article, the syn and anti isomers of benzotris(norbornadiene) 7, the only molecules that include both features known to lead to bond length alternation in benzenes, i.e., bicyclic ring strain and π-π interaction, have been synthesized from 2,3-dibromonorbornadienes using butyllithium and copper(I) iodide.
TL;DR: In this article, a polypentynoate containing mesogenic groups was stereoregularly polymerized using a Rh complex catalyst, [Rh(norbornadiene)Cl]2, in the presence of triethylamine as the cocatalyst.
Abstract: Pentynoates containing mesogenic groups, i.e., HC[dbnd]CCH2CH2-COOR (R = dihydrocholesteryl and p-methoxybiphenyl) were stereoregularly polymerized using a Rh complex catalyst, [Rh(norbornadiene)Cl]2, in the presence of triethylamine as the cocatalyst. The structure of the polymer obtained was compared with that of an analogous polymer prepared using the metathesis catalyst WCI6 in dioxane by 13C-NMR and laser Raman spectroscopic methods. The data indicated that the polypentynoate polymerized with the Rh complex has a cis-transoid form which allowed us to observe the two clear carbon signals C[dbnd]CH of the main chain in the 13C-NMR spectrum. The polypentynoate prepared using the WCI6 catalyst was found to have the trans-transoid conjugation length with N c[dbnd]c ≉ 7, which did not allow observation of the clear carbon signals of the main chain in the 13C-NMR spectrum.
TL;DR: Alkoxide (MeO-, EtO-, iPrO-, tBuO- and 2-BuO-) addition occurs at an olefinic carbon of Rh(Tripod)(NBD)+ (NBD = norbornadiene) to give Rh(tripod) 2-alkoxynorborn-4-en-1-yl as mentioned in this paper.
TL;DR: In this paper, a 1 : 1 molar ratio was obtained for the first time for the tetradentate [Ti(η5-C5H4PPh2)2(SR)2] ligand, where the P atoms were replaced by cyclopentadienyldiphenylphosphines co-ordinated by the S atoms.
Abstract: The complexes [(OC)4Mo(µ-Ph2PC5H4)2Ti(SR)2](R = Et 1 or Ph 2), [{Mo(CO)4}2{µ-(Ph2PC5H4)2Ti(SR)2}](R = Et 3 or Ph 4) and [(OC)4Mo(µ-Ph2PC5H4)2Ti(µ-SPh)2M(C6F5)2](M = Pt 5 or Pd 6) have been prepared and characterized. Complexes 1 and 2 were obtained by reaction of [Ti(η5-C5H4PPh2)2(SR)2] and [Mo(CO)4(nbd)](nbd = norbornadiene) in 1 : 1 molar ratio by replacement of the nbd by two cyclopentadienyldiphenylphosphines co-ordinated by the P atoms. The ability of the S atoms in the thiolate ligands to act as Lewis bases leads to a further increase in nuclearity. Thus, when the reaction was carried out in a 1 : 3 molar ratio, heterotrinuclear complexes 3 and 4 were obtained. The crystal structure of 4 showed that the titanium mononuclear compound acts as a symmetric S,P-bridging tetradentate ligand towards two Mo(CO)4 fragments. Compound 2 reacted with cis-[M(C6F5)2(thf)2](M = Pt or Pd, thf = tetrahydrofuran) to give 5 and 6, respectively. The crystal structure of 5 showed that 2 acts as an S,S-bidentate metalloligand towards the M(C6F5)2 fragment. It is remarkable that both structures reveal a different co-ordination mode of the tetradentate [Ti(η5-C5H4PPh2)2(SR)2] ligand.
TL;DR: The electron donoracceptor photo-reaction of norbornadiene (N)dN with 1-cyano-naphthalene (CNN) in benzene yields four cycloadducts, 1−4 as discussed by the authors.
TL;DR: In this article, photoinduced valence isomerization of norbornadiene to quadricyclane in polymer P1-2 and P3 was achieved by irradiation of visible light (wavelength, greater than 350 nm).
Abstract: Two new kinds of polymer, copolymer P1–2 and homopolymer P3, containing norbornadiene and carbazole pendants were synthesized. The photoinduced valence isomerizations of norbornadiene to quadricyclane in polymer P1–2 and P3 were achieved by irradiation of visible light (wavelength, greater than 350 nm) and an electron transfer mechanism was proposed. The back isomerization from quadricyclane to norbornadiene was also carried out for the polymer systems.
TL;DR: In this article, a new synthesis for (Me3Si)2PH using a LiAlH4/PH3 phosphinating reagent is described, which yields new compounds characterized by spectral (31P, 13C, and 1H NMR, IR, and MS) data.
Abstract: Radical reactions have been studied between Me3SiPH2 or (Me3Si)2PH and selected mono- and dialkenes, cyclohexene, 1-hexene, Ph2PCHCH2, 1,5-octadiene, norbornadiene, and 1,4-pentadiene, a series chosen for their range of reactivities. The Me3SiPH2/alkene reactions [alkene in brackets] yield the following: [1-hexene], Me3SiP(H)(n-C6H13) (8), Me3SiP(n-C6H13)2 (9); [Ph2PCHCH2], (Ph2PCH2CH2)2PSiMe3 (12); [1,4-pentadiene], Me3SiP(CH2)5 (14); [norbornadiene], Me3SiP(H)C7H9 (16A/16B). The (Me3Si)2PH/alkene reactons [alkene in brackets] yield the following: [Ph2PCHCH2], Ph2PCH2CH2P(SiMe3)2 (18); [norbornadiene], (Me3Si)2PC7H9 (20). A new synthesis for (Me3Si)2PH using a LiAlH4/PH3 phosphinating reagent is described. Solvolysis of 8, 9, 12, 14, 16A/16B, 18, and 20 yields H2P(n-C6H13) (10), HP(n-C6H13)2 (11), (Ph2PCH2CH2)2PH (13), (CH2)5PH (15), H2PC7H9 (17), and Ph2PCH2CH2PH2 (19). New compounds are characterized by spectral (31P, 13C, and 1H NMR, IR, and MS) data. Relative reactivities of phosphines in the (Me3S...
TL;DR: In this article, a polynortricyclene structure was obtained by using initiators such as AlCl3, Et3Al, AZBN, and n-butyl lithium.
Abstract: Norbornadiene was polymerized, in moderate yield by MoCl5 or EtAlCl2. By using both components together, an increase in reaction rates and in polymer yields were observed. By the optimization of the reaction conditions, 100% of polymer yield was achieved. For comparison, the polymerization of the NBD was also accomplished by using initiators such as AlCl3, Et3Al, AZBN, and n-butyl lithium. All the obtained polymers gave similar IR and NMR spectra indicating the presence of the polynortricyclene structures. Though they show different molecular weight distribution, the solubilities of the polymers (obtained using MoCl5, AlCl3, EtAlCl2, and MoCl5/EtAlCl2) are very similar. DTA analyses show that the polymers (obtained by using MoCl5/EtAlCl2 pair or n-butyl lithium or Et3Al) have high thermal stabilities whereas all the other polymers are unstable in air. © 1996 John Wiley & Sons, Inc.
TL;DR: In this article, the tri-and tetra-ruthenium clusters were shown to have organo-cluster interactions similar to those found on the Pt(111) surface, in which the bicyclic ring straddles a trimetallic face, coordinating through one alkenic bond and an agostic C-H⋯M interaction.
TL;DR: Pseudo-first-order rate constants have been determined for several 7-substituted norbornadienes in their nickel-catalyzed homo-Diels−Alder cycloaddition with methyl vinyl ketone as mentioned in this paper.
Abstract: Pseudo-first-order rate constants have been determined for several 7-substituted norbornadienes in their nickel-catalyzed homo-Diels−Alder cycloaddition with methyl vinyl ketone. The rate of reaction was slightly influenced by the nature of the substituent. Relative reactivities followed the order 7-Ph > H > 7-OTIPS. The observed activation parameters (ΔH⧧ = 15−18 kcal/mol; ΔS⧧ = −19 to −24 cal/mol K) were also affected by the 7-substituent and are in good agreement with those established for reductive elimination from related nickel phosphine complexes. With regard to regioselectivity, the more reactive norbornadiene was also the less selective. Force field modeling studies of possible organonickel intermediates suggest that the preferred exo selectivity arises from steric interactions between the dienophile substituent and the phosphine ligands. Good qualitative and quantitative agreement with observed exo stereoselectivity was found with three of the five model systems studied. Of these three models, r...
TL;DR: In this article, the use of ab initio molecular orbital theory to treat electron-transfer catalysis by metal ions and closely related subjects is described and the theoretical principles involved in hole-catalysis (acceleration of a reaction by one-electron oxidation) are examined using the norbornadiene/quadricyclane radical cation rearrangement as an example.
Abstract: The use of ab initio molecular orbital theory to treat electron-transfer catalysis by metal ions and closely related subjects is described. The theoretical principles involved in “hole-catalysis” (acceleration of a reaction by one-electron oxidation) are first examined using the norbornadiene/quadricyclane radical cation rearrangement as an example. The theoretical techniques necessary to obtain reliable results for radical and radical ion systems are also discussed. Examples of calculational studies on hole-catalyzed cycloadditions, sigmatropic rearrangements and electrocyclic reactions are given. The basic principles governing the energetics of electron-transfer between metal ions and organic substrates are described. Finally, calculational examples of electron-transfer catalysis by metal ions are treated. The examples include 1,3-hydrogen shifts, cyclopropane ring-opening, ethylene dimerization, C-C bond activation, and cycloalkane and oxirane ring-opening.
TL;DR: In this paper, the results of a single-crystal X-ray diffraction study of [RhRu4H(nbd)(CO)12B(AuPPh3] were confirmed by the results from a single crystal diffraction of the rh2Ru4B-containing compound.
Abstract: The reaction of the butterfly anion [Ru4H(CO)12BH]– with [{Rh(η5-C5Me5)Cl2}2] gave the novel boron-containing cluster [RhRu4H2(η5-C5Me5)(µ-Cl)(CO)12B] which has been characterised spectroscopically and by X-ray crystallography. Consistent with the 78 valence-electron (v.e.) count, the five metal atoms adopt an open skeletal structure which can be described as an ‘envelope’(or an edge-bridged square) geometry. In contrast, when [Ru4H(CO)12BH]– reacted with [{Rh(nbd)Cl}2](nbd = norbornadiene) and [Au(PR3)Cl](R = Ph, C6H11 or 2-MeC6H4), boride clusters containing both RhRu4B and Rh2Ru4B skeletons were obtained. The presence of the gold(I) phosphine is necessary to trap the RhRu4B-containing product. The Rh2Ru4B clusters possess octahedral frameworks and are related to the previously reported [Rh2Ru4(CO)16B(AuPR3)] compounds. However, the incorporation of only one rhodium fragment leads to the clusters [RhRu4H(nbd)(CO)12B(AuPR3)], and a square-based pyramidal RhRu4 framework (consistent with a 74 v.e. count) has been confirmed by the results of a single-crystal X-ray diffraction study of [RhRu4H(nbd)(CO)12B(AuPPh3)]. Variable-temperature 1H NMR spectroscopic data for the clusters [RhRu4H(nbd)(CO)12B(AuPR3)](R = Ph, C6H11 or 2-MeC6H4) indicate fluxional behaviour involving the norbornadiene ligand and the gold(I) phosphine unit. The reaction of [RhRu4H(nbd)(CO)12B(AuPR3)](R = Ph or C6H11) with CO gave [RhRu4H(CO)14B(AuPR3)].
TL;DR: The norbornadiene(terpyridine) complex [Mo(CO)(C 7 H 8 )(terpy)I]I] as mentioned in this paper was obtained in two steps from either KPF 6 in methanol or AgSbF 6 in CH 2 Cl 2.
TL;DR: In this article, the bimetallics Cp 2 Nb(μ-PPh 2 )(μ -CO)M(CO) 3 (PMe 2 H)(M = Cr, W) were prepared by UV irradiation of the dinuclear monobridged complexes.