Showing papers on "Intramolecular force published in 2015"
TL;DR: The role of sulfur interactions in protein structure and function is discussed and although relatively rare, intermolecular interactions between ligand C-S σ* orbitals and proteins are illustrated.
Abstract: Electron deficient, bivalent sulfur atoms have two areas of positive electrostatic potential, a consequence of the low-lying σ* orbitals of the C–S bond that are available for interaction with electron donors including oxygen and nitrogen atoms and, possibly, π-systems. Intramolecular interactions are by far the most common manifestation of this effect, which offers a means of modulating the conformational preferences of a molecule. Although a well-documented phenomenon, a priori applications in drug design are relatively sparse and this interaction, which is often isosteric with an intramolecular hydrogen-bonding interaction, appears to be underappreciated by the medicinal chemistry community. In this Perspective, we discuss the theoretical basis for sulfur σ* orbital interactions and illustrate their importance in the context of drug design and organic synthesis. The role of sulfur interactions in protein structure and function is discussed and although relatively rare, intermolecular interactions betwe...
514 citations
TL;DR: It is demonstrated that the proximity and sufficient coupling through bond or space in pentacene dimers is enough to induce intramolecular SF where two triplets are generated on one molecule.
Abstract: Singlet fission (SF) has the potential to supersede the traditional solar energy conversion scheme by means of boosting the photon-to-current conversion efficiencies beyond the 30% Shockley–Queisser limit. Here, we show unambiguous and compelling evidence for unprecedented intramolecular SF within regioisomeric pentacene dimers in room-temperature solutions, with observed triplet quantum yields reaching as high as 156 ± 5%. Whereas previous studies have shown that the collision of a photoexcited chromophore with a ground-state chromophore can give rise to SF, here we demonstrate that the proximity and sufficient coupling through bond or space in pentacene dimers is enough to induce intramolecular SF where two triplets are generated on one molecule.
337 citations
TL;DR: In this paper, triplet photosensitization was used to demonstrate intramolecular singlet fission (iSF) with triplet yields approaching 200% per absorbed photon in a series of bipentacenes.
Abstract: Singlet fission (SF) has the potential to significantly enhance the photocurrent in single-junction solar cells and thus raise the power conversion efficiency from the Shockley–Queisser limit of 33% to 44%. Until now, quantitative SF yield at room temperature has been observed only in crystalline solids or aggregates of oligoacenes. Here, we employ transient absorption spectroscopy, ultrafast photoluminescence spectroscopy, and triplet photosensitization to demonstrate intramolecular singlet fission (iSF) with triplet yields approaching 200% per absorbed photon in a series of bipentacenes. Crucially, in dilute solution of these systems, SF does not depend on intermolecular interactions. Instead, SF is an intrinsic property of the molecules, with both the fission rate and resulting triplet lifetime determined by the degree of electronic coupling between covalently linked pentacene molecules. We found that the triplet pair lifetime can be as short as 0.5 ns but can be extended up to 270 ns.
311 citations
TL;DR: In this paper, a series of g-C3N4-based intramolecular donor-acceptor copolymers (aromatics-incorporated g-c 3N4) via nucleophilic substitution/addition reactions were presented.
Abstract: The construction of intramolecular donor–acceptor conjugated copolymers has been devised for years to enhance the mobility of charge carriers in an organic photovoltaic field; however, surprisingly, similar strategies have not been reported in polymeric photocatalytic systems for promoting the separation of charge carriers. Graphitic carbon nitride (g-C3N4) is an emerging polymeric visible-light photocatalyst with high stability but still low photocatalytic efficiency. Here, we prepared a series of g-C3N4-based intramolecular donor–acceptor copolymers (aromatics-incorporated g-C3N4) via nucleophilic substitution/addition reactions. The copolymer showed remarkably enhanced and stable visible-light photocatalytic hydrogen evolution performance. The intramolecular charge transfer transition is first proposed to explain the photocatalytic activity of g-C3N4-based photocatalysts under long-wavelength-light irradiation.
274 citations
TL;DR: This work demonstrates that strong intrachain donor-acceptor interactions are a key design feature for organic materials capable of intramolecular singlet fission, and shows that triplet populations can be generated with yields up to 170%.
Abstract: Embodiments of the present invention provides compounds, compositions, and methods for their preparation that provide efficient intramolecular fission, such that local order and strong nearest neighbor coupling is no longer a design constraint. Inventive materials include organic oligomers and polymers designed to exhibit strong intrachain donor-acceptor interactions and provide intramolecular singlet fission, whereby triplet populations can be generated in very high yields of, e.g., 170% or more. The inventive disclosure is directed to polymers of the general formula: [SA-SD]n with a strong electron acceptor (SA), a strong electron donor (SD), and n a positive integer equal to or greater than two; methods for their preparation and monomers used therein, blends, mixtures and formulations containing them; the use of the polymers, blends, mixtures and formulations as semiconductors in organic electronic (OE) devices, especially in organic photovoltaic (OPV) devices, and to OE and OPV devices comprising these polymers, blends, mixtures or formulations.
272 citations
TL;DR: Based on the new ESIPT mechanism, the observed fluorescence quenching can be satisfactorily explained and the potential barrier heights among the local minima on the S1 surface imply competitive single and double proton transfer branches in the mechanism.
Abstract: The excited state intramolecular proton transfer (ESIPT) mechanisms of 2-(2-hydroxyphenyl)benzoxazole (HBO), bis-2,5-(2-benzoxazolyl)-hydroquinone (BBHQ) and 2,5-bis(5′-tert-butyl-benzoxazol-2′-yl)hydroquinone (DHBO) have been investigated using time-dependent density functional theory (TDDFT). The calculated vertical excitation energies based on the TDDFT method reproduced the experimental absorption and emission spectra well. Three kinds of stable structures were found on the S1 state potential energy surface (PES). A new ESIPT mechanism that differs from the one proposed previously (Mordzinski et al., Chem. Phys. Lett., 1983, 101, 291. and Lim et al., J. Am. Chem. Soc., 2006, 128, 14542.) is proposed. The new mechanism includes the possibility of simultaneous double proton transfer, or successive single transfers, in addition to the accepted single proton transfer mechanism. Hydrogen bond strengthening in the excited state was based on primary bond lengths, angles, IR vibrational spectra and hydrogen bond energy. Intramolecular charge transfer based on the frontier molecular orbitals (MOs) also supports the proposed mechanism of the ESIPT reaction. To further elucidate the proposed mechanism, reduced dimensionality PESs of the S0 and S1 states were constructed by keeping the O–H distance fixed at a series of values. The potential barrier heights among the local minima on the S1 surface imply competitive single and double proton transfer branches in the mechanism. Based on the new ESIPT mechanism, the observed fluorescence quenching can be satisfactorily explained.
248 citations
TL;DR: The synthesis of a borylene dicarbonyl complex is presented, the first multicarbonyL complex of a main-group element prepared using CO, and the compound is additionally stable towards ambient air and moisture.
Abstract: The ability of an atom or molecular fragment to bind multiple carbon monoxide (CO) molecules to form multicarbonyl adducts is a fundamental trait of transition metals. Transition-metal carbonyl complexes are vital to industry, appear naturally in the active sites of a number of enzymes (such as hydrogenases), are promising therapeutic agents, and have even been observed in interstellar dust clouds2. Despite the wealth of established transition-metal multicarbonyl complexes3, no elements outside groups 4 to 12 of the periodic table have yet been shown to react directly with two or more CO units to form stable multicarbonyl adducts. Here we present the synthesis of a borylene dicarbonyl complex, the first multicarbonyl complex of a main-group element prepared using CO. The compound is additionally stable towards ambient air and moisture. The synthetic strategy used—liberation of a borylene ligand from a transition metal using donor ligands—is broadly applicable, leading to a number of unprecedented monovalent boron species with different Lewis basic groups. The similarity of these compounds to conventional transition-metal carbonyl complexes is demonstrated by photolytic liberation of CO and subsequent intramolecular carbon–carbon bond activation.
247 citations
TL;DR: A manganese catalyst is reported that aminates C–H bonds via a mechanism that lies between that of reactive noble metals (concerted) and chemoselective base metals (stepwise), demonstrating reactivity and selectivity unusual for previously known catalysts.
Abstract: C-H bond oxidation reactions underscore the existing paradigm wherein high reactivity and high selectivity are inversely correlated. The development of catalysts capable of oxidizing strong aliphatic C(sp(3))-H bonds while displaying chemoselectivity (that is, tolerance of more oxidizable functionality) remains an unsolved problem. Here, we describe a catalyst, manganese tert-butylphthalocyanine [Mn((t)BuPc)], that is an outlier to the reactivity-selectivity paradigm. It is unique in its capacity to functionalize all types of C(sp(3))-H bond intramolecularly, while displaying excellent chemoselectivity in the presence of π functionality. Mechanistic studies indicate that [Mn((t)BuPc)] transfers bound nitrenes to C(sp(3))-H bonds via a pathway that lies between concerted C-H insertion, observed with reactive noble metals such as rhodium, and stepwise radical C-H abstraction/rebound, as observed with chemoselective base metals such as iron. Rather than achieving a blending of effects, [Mn((t)BuPc)] aminates even 1° aliphatic and propargylic C-H bonds, demonstrating reactivity and selectivity unusual for previously known catalysts.
218 citations
TL;DR: Mechanistic studies indicate that the amide substrate can be selectively homolyzed via PCET in the presence of the thiophenol, despite a large difference in bond dissociation free energies between these functional groups.
Abstract: Here we report a ternary catalyst system for the intramolecular hydroamidation of unactivated olefins using simple N-aryl amide derivatives. Amide activation in these reactions occurs via concerted proton-coupled electron transfer (PCET) mediated by an excited state iridium complex and weak phosphate base to furnish a reactive amidyl radical that readily adds to pendant alkenes. A series of H-atom, electron, and proton transfer events with a thiophenol cocatalyst furnish the product and regenerate the active forms of the photocatalyst and base. Mechanistic studies indicate that the amide substrate can be selectively homolyzed via PCET in the presence of the thiophenol, despite a large difference in bond dissociation free energies between these functional groups.
214 citations
TL;DR: DFT calculations suggest that the O-O bond formation takes place by an intramolecular direct coupling mechanism rather than by a nucleophilic attack of water on the high-oxidation-state Cu(IV)=O moiety.
Abstract: Electrocatalytic water oxidation using the oxidatively robust 2,7-[bis(2-pyridylmethyl)aminomethyl]-1,8-naphthyridine ligand (BPMAN)-based dinuclear copper(II) complex, [Cu2(BPMAN)(μ-OH)](3+), has been investigated. This catalyst exhibits high reactivity and stability towards water oxidation in neutral aqueous solutions. DFT calculations suggest that the O-O bond formation takes place by an intramolecular direct coupling mechanism rather than by a nucleophilic attack of water on the high-oxidation-state Cu(IV)=O moiety.
206 citations
TL;DR: The calculated results show that the intramolecular hydrogen bonds were formed in the S0 state, and upon excitation, the intra-chemical hydrogen bonds between -OH group and pyridine-type nitrogen atom would be strengthened in theS1 state, which can facilitate the proton transfer process effectively.
Abstract: The excited state intramolecular proton transfer (ESIPT) mechanisms of 1,8-dihydroxydibenzo[a,h]phenazine (DHBP) in toluene solvent have been investigated based on time-dependent density functional theory (TD-DFT). The results suggest that both a single and double proton transfer mechanisms are relevant, in constrast to the prediction of a single one proposed previously (Piechowska et al. J. Phys. Chem. A 2014, 118, 144–151). The calculated results show that the intramolecular hydrogen bonds were formed in the S0 state, and upon excitation, the intramolecular hydrogen bonds between −OH group and pyridine-type nitrogen atom would be strengthened in the S1 state, which can facilitate the proton transfer process effectively. The calculated vertical excitation energies in the S0 and S1 states reproduce the experimental UV–vis absorption and fluorescence spectra well. The constructed potential energy surfaces of the S0 and S1 states have been used to explain the proton transfer process. Four minima have been f...
TL;DR: Empirical correlations were observed among the hydrogen-bonding strength, ESIPT kinetics, and thermodynamics, demonstrating a trend that the stronger N-H···N hydrogen bond leads to a faster ESIPt, as experimentally observed, and a more exergonic reaction thermodynamics.
Abstract: A series of new amino (NH)-type hydrogen-bonding (H-bonding) compounds comprising 2-(2′-aminophenyl)benzothiazole and its extensive derivatives were designed and synthesized. Unlike in the hydroxyl (OH)-type H-bonding systems, one of the amino hydrogens can be replaced with electron-donating/withdrawing groups. This, together with a versatile capability for modifying the parent moiety, makes feasible the comprehensive spectroscopy and dynamics studies of amino-type excited-state intramolecular proton transfer (ESIPT), which was previously inaccessible in the hydroxyl-type ESIPT systems. Empirical correlations were observed among the hydrogen-bonding strength (the N–H bond distances and proton acidity), ESIPT kinetics, and thermodynamics, demonstrating a trend that the stronger N–H···N hydrogen bond leads to a faster ESIPT, as experimentally observed, and a more exergonic reaction thermodynamics. Accordingly, ESIPT reaction can be harnessed for the first time from a highly endergonic type (i.e., prohibitio...
TL;DR: The use of rhodium(II) catalysts enabled us to widen the scope of this transformation for the synthesis of medium-sized heterocyclic scaffolds incorporating an eight-membered ring, and set a useful basis for the development of other reaction pathways involving metal carbenoids generated from these readily available families of substituted cyclopropenes.
Abstract: ConspectusActivation of unsaturated carbon–carbon bonds by means of transition metal catalysts is an exceptionally active research field in organic synthesis In this context, due to their high ring strain, cyclopropenes constitute an interesting class of substrates that displays a versatile reactivity in the presence of transition metal catalysts Metal complexes of vinyl carbenes are involved as key intermediates in a wide variety of transition metal-catalyzed ring-opening reactions of cyclopropenes Most of the reported transformations rely on intermolecular or intramolecular addition of nucleophiles to these latter reactive species This Account focuses specifically on the reactivity of carbenoids resulting from the ring-opening of cyclopropenes in cyclopropanation and C–H insertion reactions, which are arguably two of the most representative transformations of metal complexes of carbenesCompared with the more conventional α-diazo carbonyl compounds, the use of cyclopropenes as precursors of metal ca
TL;DR: The iridium-catalyzed dehydrogenative cyclization of 2-aminobiphenyls proceeds smoothly in the presence of a copper cocatalyst under air as a terminal oxidant through intramolecular direct C-H amination to produce N-H carbazoles.
TL;DR: Intramolecular asymmetric carbopalladation of N-aryl acrylamides followed by intermolecular trapping of the resulting σ-C(sp(3))-Pd complex by azoles afforded 3,3-disubstituted oxindoles in good yields with excellent enantioselectivities.
Abstract: Intramolecular asymmetric carbopalladation of N-aryl acrylamides followed by intermolecular trapping of the resulting σ-C(sp(3))-Pd complex by azoles afforded 3,3-disubstituted oxindoles in good yields with excellent enantioselectivities. Two C-C bonds were created with concurrent formation of an all-carbon quaternary stereocenter. Oxadiazole substituted oxindoles were subsequently converted to pyrroloindolines by an unprecedented reductive cyclization protocol. The utility of this chemistry was illustrated by an enantioselective synthesis of (+)-esermethole.
TL;DR: During this study it was observed that the steric hindrance of chiral ligands had a profound influence on the reactivity and enantioselectivity of the reaction, and might hold the key to accomplishing conventionally challenging asymmetric C-H silylations.
Abstract: Reported herein is the rhodium-catalyzed enantioselective CH bond silylation of the cyclopentadiene rings in Fe and Ru metallocenes. Thus, in the presence of (S)-TMS-Segphos, the reactions took place under very mild conditions to afford metallocene-fused siloles in good to excellent yields and with ee values of up to 97 %. During this study it was observed that the steric hindrance of chiral ligands had a profound influence on the reactivity and enantioselectivity of the reaction, and might hold the key to accomplishing conventionally challenging asymmetric CH silylations.
TL;DR: Diverse and controllable pathways induced by palladium-catalyzed intramolecular Heck reaction of N-vinylacetamides for the synthesis of nitrogen-containing products in reasonable to high yields via tuning the phosphine ligands and bases are reported.
Abstract: Diverse and controllable pathways induced by palladium-catalyzed intramolecular Heck reaction of N-vinylacetamides for the synthesis of nitrogen-containing products in reasonable to high yields via tuning the phosphine ligands and bases are reported. Domino reactions including unique β-N–Pd elimination, 1,4-Pd migration, or direct acyl C–H bond functionalization were found to be involved forming different products, respectively. Given the ability of using the same starting material to generate diverse products via completely different chemoselective processes, these current methodologies offer straightforward access to valuable nitrogen-containing products under mild reaction conditions as well as inspire the discovery of novel reactions.
TL;DR: DFT (M06-2X) calculations show that the preferred pathway involves an iodonium cation intermediate and proceeds via an energetically concerted transition state, through hydride transfer followed by the spontaneous C-N bond formation, which leads to the experimentally observed amination at a chiral center without loss of stereochemical information.
Abstract: A new strategy is reported for intramolecular sp3 C–H amination under mild reaction conditions using iodoarene as catalyst and m-CPBA as oxidant. This C–H functionalization involving iodine(III) reagents generated in situ occurs readily at sterically hindered tertiary C–H bonds. DFT (M06-2X) calculations show that the preferred pathway involves an iodonium cation intermediate and proceeds via an energetically concerted transition state, through hydride transfer followed by the spontaneous C–N bond formation. This leads to the experimentally observed amination at a chiral center without loss of stereochemical information.
TL;DR: Two AIE-active chiral BINOL-based O-BODIPY enantiomers were synthesized and showed mirror-image red-color CPL induced via intramolecular energy transfer, indicating that the chirality of electronic ground and excited states is stable and independent of aggregation.
TL;DR: This reaction is operationally trivial in both execution and product isolation (only requiring concentration followed by purification) and accommodates a broad range of substrates.
TL;DR: The first catalytic trifluoromethoxylation of unactivated alkenes has been developed, in which Pd(CH3CN)2Cl2 was used as catalyst, AgOCF3 as trifluent source, and Selectfluor-BF4 as oxidant.
Abstract: The first catalytic trifluoromethoxylation of unactivated alkenes has been developed, in which Pd(CH3CN)2Cl2 was used as catalyst, AgOCF3 as trifluoromethoxide source, and Selectfluor-BF4 as oxidant. A variety of 3-OCF3 substituted piperidines were selectively obtained in good yields. Direct evidence was provided to address the facile reductive elimination of PdIV–OCF3 complex to form sp3 C–OCF3 bond.
TL;DR: It is demonstrated that the interactions of the exciton with intermolecular vibrational modes are highly sensitive to the stacking geometry of the crystal and can, in certain cases, significantly accelerate SF.
Abstract: We report numerical simulations based on a non-Markovian density matrix propagation scheme of singlet fission (SF) in molecular crystals. Ab initio electronic structure calculations were used to parametrize the exciton and phonon Hamiltonian as well as the interactions between the exciton and the intramolecular and intermolecular vibrational modes. We demonstrate that the interactions of the exciton with intermolecular vibrational modes are highly sensitive to the stacking geometry of the crystal and can, in certain cases, significantly accelerate SF. This result may help in understanding the fast SF experimentally observed in a broad range of molecular crystals and offers a new direction for the engineering of efficient SF sensitizers.
TL;DR: This feature article is going to cover the methodology related to the construction of N-heterocycles through oxidative intramolecular N-H/X-H coupling.
TL;DR: A general approach for the formation of five-membered saturated heterocycles by intramolecular C(sp(3))-H functionalization is reported, showing the reaction to be amenable to gram scale and judicious choice of reaction conditions allowed for stereodivergence.
Abstract: A general approach for the formation of five-membered saturated heterocycles by intramolecular C(sp3)–H functionalization is reported. Using N-sulfonyltriazoles as Rh(II) azavinyl carbene equivalents, a wide variety of stereodefined cis-2,3-disubstituted tetrahydrofurans were obtained with good to excellent diastereoselectivity from readily available acyclic precursors. The reaction is shown to be amenable to gram scale, and judicious choice of reaction conditions allowed for stereodivergence, providing selective access to the trans diastereomer in good yield. The resulting products were shown to be valuable intermediates for the direct preparation of fused N-heterotricycles in one step by intramolecular C–H amination or Pictet–Spengler cyclization.
TL;DR: The chirality of vinyl aziridine-alkyne substrates can be completely transferred to the cycloadducts, representing an atom-economic and enantiospecific protocol for the construction of fused 2,5-dihydroazepines for the first time.
Abstract: By taking advantage of vinyl aziridines as a heteroatom-containing five-atom component in rhodium-catalyzed intramolecular formal hetero-[5 + 2] cycloaddition reactions with alkynes, a highly efficient method for the synthesis of fused azepine derivatives at 30 °C was developed. The reaction has broad substrate scope and tolerates a wide range of functional groups. The chirality of vinyl aziridine-alkyne substrates can be completely transferred to the cycloadducts, representing an atom-economic and enantiospecific protocol for the construction of fused 2,5-dihydroazepines for the first time.
TL;DR: The palladium-catalyzed enantioselective intramolecular C-H arylation of N-(2-haloaryl)-P,P-diphenylphosphinic amides furnishes P-stereogenic phosphine oxide derivatives in 61-99% yield with 88-97% ee.
TL;DR: The design, synthesis, and both experimental and theoretical studies of several novel 9-(acylimino)- and 9-(sulfonylimino)pyronin derivatives containing either an oxygen or a silicon atom at position 10 are reported, and they represent excellent candidates for biochemical and biological applications as fluorescent tags and indicators for multichannel imaging.
Abstract: The design, synthesis, and both experimental and theoretical studies of several novel 9-(acylimino)- and 9-(sulfonylimino)pyronin derivatives containing either an oxygen or a silicon atom at position 10 are reported. These compounds, especially the Si analogues, exhibit remarkably large Stokes shifts (around 200 nm) while still possessing a high fluorophore brightness, absorption bands in the near-UV and visible part of the spectrum, and high thermal and photochemical stabilities in protic solvents. The reason for the observed large Stokes shifts is an intramolecular charge-transfer excitation of an electron from the HOMO to the LUMO of the chromophore, accompanied by elongation of the C9–N bond and considerable solvent reorganization due to hydrogen bonding to the solvent. Due to the photophysical properties of the studied compounds and their facile and high-yielding synthesis, as well as a simple protocol for their bioorthogonal ligation to a model saccharide using a Huisgen alkyne–azide cycloaddition, ...
TL;DR: Evaluating the frontier orbital interactions between the donor and acceptor effectively predicts whether chromophores planarize or twist in the excited state.
Abstract: A D–A (donor–acceptor)-type chromophore may twist or flatten in its excited state to form a TICT (twisted intramolecular charge transfer) state or a PICT (planar intramolecular charge transfer) state, respectively. What is the driving force behind this twisting or planarization? Which geometry will occur for a certain D–A chromophore? To answer these questions, both fragment orbital interaction and excited state energy decomposition analyses were performed on several classical TICT/PICT molecules. Three driving forces were identified, namely, energy gap, hole–electron interactions, and excited state relaxation. The contributions of these driving forces in various types of molecules were analyzed to determine how the molecular structure affects them. The energy gap difference between the twisted and planar geometries was found to play a decisive role in most situations. Thus, evaluating the frontier orbital interactions between the donor and acceptor effectively predicts whether chromophores planarize or twist in the excited state.
TL;DR: The first synthesis of planar-chiral benzosiloloferrocenes was achieved by the intramolecular reaction of 2-(dimethylhydrosilyl)arylferrocenes by the enantioselective cross dehydrogenative coupling of an sp(2) C-H bond of ferrocene with a Si-H Bond.
TL;DR: It is demonstrated that the ESIPT could successfully proceed in QP-II and that the PT emission would be quenched by the ISC process.
Abstract: The dynamics of the excited-state intramolecular proton-transfer (ESIPT) reaction of quinoline–pyrazole (QP) isomers, designated as QP-I and QP-II, has been investigated by means of time-dependent density functional theory (TDDFT). A lower barrier has been found in the potential energy curve for the lowest singlet excited state (S1) along the proton-transfer coordinate of QP-II compared with that of QP-I; however, this is at variance with a recent experimental report [J. Phys. Chem. A 2010, 114, 7886–7891], in which the authors proposed that the ESIPT reaction would only proceed in QP-I due to the absence of a PT emission for QP-II. Therefore, several deactivating pathways have been investigated to determine whether fluorescence quenching occurs in the PT form of QP-II (PT-II). The S1 state of PT-II has nπ* character, which is a well-known dark state. Moreover, the energy gap between the S1 and T2 states is only 0.29 eV, implying that an intersystem crossing (ISC) process would occur rapidly following the...