- Redox behaviour of ([fc(NPiPr2)2]Fe)2, formation of an iron-iron bond and cleavage of azobenzene
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The redox behaviour of the dimeric tetrairon complex, ([fc(NPiPr2)2]Fe)2 (where fc(NPiPr2)2 = 1,1′-(C5H4NPiPr2)2Fe) has been investigated. Upon reduction with KC8 an Fe-Fe bond is formed with the complex maintaining a high spin configuration and having the formula [K(THF)6]([fc(NPiPr2)2]Fe)2. In contrast, oxidation of the complex is ligand based; for example, addition of the 1,2-diiodoethane (I2 equivalent) results in the formation of the monomeric iron(ii) diiodide [fc(NiPr2I)2]FeI2 wherein the phosphine is oxidized. The dimeric tetrairon complex reacts photolytically with azobenzene, cleaving the NN double bond and forming the new monomeric bis(phosphoramidate) iron complex. [fc(NP(NPh)iPr2)2]Fe. Characterization of these paramagnetic complexes was accomplished by magnetic susceptibility studies and X-ray analyses.
- Pick, Fraser S.,Leznoff, Daniel B.,Fryzuk, Michael D.
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- Ring carbon functionalization of N-heterocyclic carbene ligand with ester groups. Electronic effect of ester groups on coordination properties
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Palladium complexes with an imidazol-2-ylidene ligand functionalized with ester groups at its 4,5-positions were synthesized from a readily available imidazole derivative. σ-Donation from the carbene ligand to the palladium atom is considerably weakened by functionalization with the two ester moieties.
- Hara, Kenji,Kanamori, Yoshikazu,Sawamura, Masaya
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- Picosecond kinetics of trans-cis-photoisomerisations: from jet-cooled molecules to compressed solutions
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The understanding of photoisomerisation reactions involving large amplitude motion is discussed with special emphasis on the merits of systematic studies over wide ranges of physical conditions. It appears that the friction in such cases is proportional to macroscopic solvent viscosity η, and the original Kramers theory is sufficient to describe the effect of friction in the range from intermediate to strong damping, i.e. from low viscosity fluid to compressed high viscosity liquid solution. This one-dimensional model may be connected to multidimensional unimolecular rate theory to obtain a representation of the density dependence of the rate coefficient down to the thermal collisionless regime. The apparent failure of this approach in the case of /rans-stilbene can be traced to modifications of the excited state PES by the solvent. This interpretation is consistent over the entire range of physical conditions studied, starting at the jet-cooled isolated molecule and solvent cluster and ending in compressed liquid solution at very high viscosities. It is shown that detailed information about the PES is urgently needed to provide safer ground for a profound understanding of the photoisomerisation dynamics. VCH Verlagsgesellschafl mbH, 1997.
- Schroeder, J?rg
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- Cluster and barrier effects in the temperature and pressure dependence of the photoisomerization of trans-stilbene
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The pressure and temperature dependence of the photoisomerization rate coeficient of trans-stilbene in the S1 state have been measured in the solvents C2H6, C3H8, C4H10, Xe, Co2, SF6, and CHF3.At constant temperature, the pressure dependences up to 6 kbar can be well represented by the Kramers-Smoluchowski model.The comparison of results in different solvents cleary indicates the importance of reactant-solvent cluster formation modifying the height and imaginary frequency of the barrier.The change of the temperature dependence with pressure points towards a multidimensional barrier of nonseparable character.Multidimensional barrier effects manifest themselves most clearly via the temperature dependence of the rate coefficient in the Kramers-Smoluchowski limit.
- Schroeder, J.,Schwarzer, D.,Troe, J.,Voss, F.
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- A parahydrogen study of catalytic hydrogenation by diphosphane-substituted triruthenium clusters
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The diphosphane-substituted clusters [Ru3(CO) 10(dppe)] and [Ru3(CO)8(dppe)2] [dppe = 1,2-bis(diphenylphosphanyl)e-thane] are shown to catalytically hydrogenate diphenylacetylene. This process is high
- Prestwich, Tom G.,Blazina, Damir,Duckett, Simon B.,Dyson, Paul J.
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- Visible-Light-Induced, Metal-Free Carbene Insertion into B-H Bonds between Acylsilanes and Pinacolborane
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Carbene insertion reactions with B-H bonds are a challenging but promising method for the synthesis of organoboranes. Herein, we report visible-light-induced B-H insertions of HBpin with acylsilane. This metal-free and operationally simple reaction proceeds in an atom-economical way with broad substrate scope under mild reaction conditions, affording a variety of important α-alkoxyorganoboronate esters in quantitative yields. Control experiments and density functional theory calculations suggest that the siloxycarbene generation from the T1 state of acylsilane and the carbene insertion into the B-H bond occurred in a concerted manner.
- Ye, Jian-Heng,Quach, Linda,Paulisch, Tiffany,Glorius, Frank
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- Cycloaddition of Dialkylalumanyl Anion toward Unsaturated Hydrocarbons in (1+2) and (1+4) Modes
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The reactivity of dialkylalumanyl anion (1) towards naphthalene, anthracene, diphenylacetylene, and (E)/(Z)-stilbenes was investigated. The compound 1 reacts with naphthalene and anthracene through (1+4) cyclization, giving Al-containing norbornadiene derivatives. In the reaction of 1 with diphenylacetylene and (E)/(Z)-stilbenes, (1+2) cyclization proceeded to form Al-C-C three-membered rings. Cyclization toward (E)- or (Z)-stilbenes solely gave a trans-cycloadduct. DFT calculations revealed that the cycloaddition of 1 with (Z)-stilbene proceeds via a single transition state with a carbanion character, which results in the selectivity towards the trans-cycloadduct.
- Nakano, Ryo,Sugita, Kengo,Yamashita, Makoto
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- Pyrene-benzoylthiophene bichromophores as selective triplet photosensitizers
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Combination of the pyrene and benzoylthiophene units constitutes an interesting approach to design bichromophoric photosensitizers with increased intersystem crossing quantum yield and enhanced selectivity. The potential of this strategy has been illustrated in the present work by using a model photoisomerization reaction. The Royal Society of Chemistry 2005.
- Perez-Prieto, Julia,Perez, Lourdes Pastor,Gonzalez-Bejar, Maria,Miranda, Miguel A.,Stiriba, Salah-Eddine
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- Donor-Stabilized Silacyclobutanone: A Precursor of 1-Silaketene via Retro-[2 + 2]-Cycloaddition Reaction at Room Temperature
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The synthesis of donor-stabilized silacyclobutanone 2 was successfully realized by the reaction of silacyclopropylidene 1 with benzaldehyde in the presence of a Lewis acid catalyst. Of particular interest, silacyclobutanone 2 evolves at room temperature via a retro-[2 + 2]-cycloaddition reaction, leading to an original NHC-stabilized 1-silaketene 4 and cis-stilbene.
- Troadec, Thibault,Lopez Reyes, Morelia,Rodriguez, Ricardo,Baceiredo, Antoine,Saffon-Merceron, Nathalie,Branchadell, Vicen?,Kato, Tsuyoshi
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- Insights into the heck reaction with PCP pincer palladium(II) complexes
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The Heck reaction of phenyl halides with styrene using a series of related PCP pincer palladium(II) complexes was studied in order to evaluate the effect of ligand structure and electronics on the catalytic activity and to investigate the nature of the catalyst species. We suggest these pincer complexes are precatalysts for highly active forms of metallic palladium. This conclusion is based on kinetic studies (induction periods, sigmoidal kinetics), Hg drop tests, quantitative poisoning experiments, and NMR studies.
- Eberhard, Michael R.
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- Solvent dielectric effects on isomerization dynamics: Investigation of the photoisomerization of 4,4'-dimethoxystilbene and t-stilbene in n-alkyl nitriles
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New data for the photoisomerization dynamics of t-stilbene and 4,4'-dimethoxystilbene in polar sovents are reported.These data demonstrate that in n-alkyl nitriles, nonassociated polar solvents, it is possible to extract a solvated barrier for the isomerization.This result is contrasted with recent studies in n-alkyl alcohols, associated polar solvents, where this separation is not possible and clarifies the origin of the changing barrier height in n-alkyl alcohols.Comparison of reduced isomerization rates with models of chemical reaction dynamics in solution are drawn.Good agreement of the data with a coupled oscillator model is found.
- Sivakumar, N.,Hoburg, E. A.,Waldeck, D. H.
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- A high yielding synthesis of [5-14C]-5H-dibenzo[a,d]cyclohepten-5-one (dibenzosuberenone) using [14C]-dimethylformamide
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A seven step synthesis of dibenzosuberenone is presented in which [14C]-DMF is used in lieu of 14CO2 to prepare the carboxylic acid intermediate. The advantages of this procedure over other commonly used methods is discussed. The title compound was obtained at a specific activity of 53 mCi/mmol (61% overall radiochemical yield).
- Kendall, John T.
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- Pd(II)-Schiff base complexes heterogenised on MCM-41 and delaminated zeolites as efficient and recyclable catalysts for the heck reaction
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We present a widely applicable approach for the preparation of Pd-complexes supported on silica-based mesoporous and laminar inorganic solids (silica gel, purely siliceous and acidic MCM-41, and delaminated zeolites ITQ-2 and ITQ-6) which involves the use of the Schiff bases 2-tert-butyl-4-methyl-6{(E)-[(2S)-1- (1-arylmethyl)pyrrolidinyl]imino}methylphenol (aryl = phenyl, 1-naphthyl, 2-naphthyl) as anchored ligands. As an extension of our research in recyclable catalytic systems we report results demonstrating the reactivity and recyclability of these systems for the Heck reaction (in a biphasic mode using ethylene glycol and toluene) and Suzuki coupling under phosphine-free conditions. The complexes are insensitive to oxygen or moisture, and no change of their activity was observed when exposed to an open system during the usual operation. No palladium black was observed after an extended reaction time and no residual palladium was detected from the filtrate at the end of the reaction.
- Gonzalez-Arellano,Corma,Iglesias,Sanchez
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- Barrier crossing and solvation dynamics in polar solvents: Photoisomerization of trans-stilbene and E,E-diphenylbutadiene in compressed alkanols
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The viscosity dependence of the photoisomerization of trans-stilbeme in compressed liquid ethanol shows deviations from a simple power law description in the viscosity range from 1 to 4 mPa s.Corresponding deviations are observed in the solvents methanol, n-propanol, and n-butanol.This behavior is attributed to a competition between solvent relaxation and barrier crossing in the S1 state of trans-stilbene.The relative time scales of barrier crossing and solvent relaxation change as the pressure increases, because the dielectric relaxation rate of the solvent decreases more rapidly with increasing viscosity than the barrier crossing rate.Consequently, the reaction takes place in an increasingly retarded solvent environment which no longer relaxes completely around the changing charge distribution of the solute along its reaction path, giving rise to "dielectric friction".In contrast to trans-stilbene, the corresponding reaction of diphenylbutadiene in n-alkanols shows a much weaker sensitivity to solute-solvent interaction and, consequently, a simple inverse viscosity dependence of the photoisomerization rate is observed in all alkanols such as described by the Kramers-Smoluchowski theory.This significant difference is probably caused by smaller sudden polarization effects along the reaction path in diphenylbutadiene.The observed dependence of the trans-stilbene barrier crossing rate on pressure is compared either to a model with density dependent effective barrier height, or to a simple continuum model of the frequency dependence of the dielectric friction in the limit of weak coupling.Neither model works well unless a very strong viscosity dependence of the dielectric relaxation time of the solvent (τDη10) is employed to obtain agreement with the observed viscosity dependence of the barrier crossing rate.
- Mohrschladt, R.,Schroeder, J.,Schwarzer, D.,Troe, J.,Voehringer, P.
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- Shape-Selective Photosensitized Isomerization of Stilbene Using a Benzophenone Incorporated Within Acid Zeolites
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A sereies of heterogeneous photosensitizers has been obtained by immobilization of 4-aminobenzophenone (ABP) within acid zeolites of medium and large pore size.The strong interaction between the amino substituent of ABP and the acid sites of the zeolite is revealed by the red-shift (ca. 50 nm) of the long wavelength absorption band in the UV/Vis spectra of the composites.ABP when included within HZSM-5 (ABP-HZSM-5) behaves as the first shape-selective photosensitizer.Thus, trans-stilbene could be photochemically isomerized to cis-stilbene in the presence of ABP-HZSM-5, while the reverse cis to trans isomerization failed.According to the relative dimensions of the zeolite hosts, ABP incorporated within HY, Hβ and HMOR showed no remarkable difference in the isomerization efficiency of both stilbene isomers.
- Baldovi, Maria V.,Corma, Avelino,Garcia, Hermenegildo,Marti, Vicente
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- Rates of Photoisomerization of trans-Stilbene in Isolated and Solvated Molecules: Experiments on the Deuterium Isotope Effect and RRKM Behavior
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In this paper we consider the dynamics of the photoisomerization of trans-stilbene and related molecules.New measurements of the deuterium isotope effect on reaction rates are presented, and details of RRKM behavior in isolated and solvated trans-stilbene are discussed.From measurements of fluorescence decay rates as a function of the excess vibrational energy in jet-cooled trans-stilbene-d12, an energy threshold to the rates is found at ca. 1200-cm-1 excess energy in the first excited singlet state.The threshold behavior is similar to that which occurs in the photoisomerization of trans-stilbene-h12.The overall magnitudes of the perdeuterio rates are smaller, however, than the perprotio ones.As with trans-stilbene-h12 themeasured rates are found to be slower than those calculated by standard RRKM theory.Nevertheless, the observed slowing of the rates upon deuteration is predicted by the theory.The results and their interpretation are discussed in light of the results of other jet studies of trans-stilbene derivatives and of studies of the photoisomerization reaction in solution.The role of intramolecular vibrational energy redistribution and the nonadiabatic influences on the reaction are also discussed.
- Felker, Peter M.,Zewail, Ahmed H.
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- Poly(2-oxazoline)s functionalized with palladium carbene complexes: Soluble, amphiphilic polymer supports for C-C coupling reactions in water
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This paper describes the synthesis and characterization of a new class of amphiphilic, watersoluble diblock copolymers based on 2-oxazoline derivatives with pendent N-heterocyclic carbene/palladium catalysts in the Hydrophobic block. The synthetic strategy involves a four-step synthesis of three functionalized monomers, each composed of a bis(imidazoline-2-ylidene)palladium(II) diiodide derivative that is covalently linked to a 2-oxazoline monomer via a flexible alkyl spacer (alkyl = butyl, hexyl, octyl). The structure of the monomers was analyzed by 1H and 13C NMR spectroscopy, MALDI-TOF, and elemental analysis. Three diblock copolymers P1-P3 with the monomers being part of the hydrophobic block were prepared by living cationic ring-opening polymerization. The structure and composition of the polymers was characterized by 1H and 13C NMR spectroscopy as well as GPC measurements and indicated rather low PDI of 1.3 and about 65% incorporation of the N-heterocyclic carbene/palladium-functionalized monomer into the polymer. Dynamic light scattering measurements of the polymers P1-P3 in water revealed aggregate formation with a hydrodynamic radius of 10-30 nm with high polydispersity as visualized by TEM micrographs. Subsequently, polymers P1-P3 were successfully utilized as a polymeric support for the Heck coupling of iodobenzene with styrene as a model reaction in water, showing high activities with turnover frequencies (TOF) up to 570 h-1 at 90°C.
- Schoenfelder, Daniel,Fischer, Karl,Schmidt, Manfred,Nuyken, Oskar,Weberskirch, Ralf
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- TRANS-STILBENE-AMINE EXCIPLEXES. STEREOELECTRONIC CONTROL OF AMINE DIMER CATION RADICAL FORMATION.
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The interaction of singlet trans-stilbene with several trialkylamines, alpha , omega -diaminoalkanes, and the bicyclic diamine Dabco in benzene solution has been investigated. The rate constants for fluorescence quenching equal or exceed the rate of diffusion and are not subject to steric hindrance. Exciplex energies and monoamine oxidation potentials show little variation with structure, suggesting that steric destabilization and inductive stabilization counterbalance each other. Intersystem crossing to yield triplet trans-stilbene is the predominant exciplex decay pathway at low amine concentrations. At higher amine concentrations, exciplex quenching by ground-state amines occurs and is subjected to a pronounced steric effect in the case of monoamines and chain-length effect in the case of diaminoalkanes.
- Hub,Schneider,Doerr,Oxman,Lewis
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- Does photoisomerization proceed in an ionic liquid?
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Photoisomerization of trans-stilbene has been investigated in an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate([bmim]PF6). It has been found that the photo-isomerization indeed proceeds in this ionic liquid with a rate much larger than that expected from its polarity and shear viscosity.
- Ozawa, Ryosuke,Hamaguchi, Hiro-O
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- Picosecond Dynamics of trans-Stilbene Photodimerization
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Picosecond absorption spectroscopy is used to examine the dynamics of the 2+2 photodimerization reaction of trans-stilbene in benzene.The quenching of the first excited singlet state of trans-stilbene by ground-state trans-stilbene occurs at the diffusion limit, 2.03 * 1010 M-1 s-1.Upon quenching, a new intermediate is formed with a λmax of 480 nm which is characteristic of the charge-transfer species.The rate of the decay of the transient species is (2.40 +/- 0.37) * 109 s-1.The assignment of the transient to the excimer or a biradicaloid species at the pericyclic minimum is discussed.
- Peters, Kevin S.,Freilich, Steven C.,Lee, Joseph
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- Direct Observation of the Rate for Cis->Trans and Trans->Cis Photoisomerization of Stilbene with Picosecond Laser Photolysis
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The rates for direct cis->trans and trans->cis photoisomerizations of stilbene in solution were measured with a newly developed monitor light source for picosecond laser photolysis in the UV region. The rate constant of the trans->cis isomerization is 1.2*1010 s-1 in hexane at 295 K. The fluorescence decay rate constant of the S1 state of trans-stilbene has the same value. Thus, the decay of the S1 state is the rate limiting step and the lifetime of an intermediate perpendicular state (1p) has to be very short. The cis->trans isomerization is very fast and the half life of the excited cis-isomer is less than a few picosecond. These observations strongly indicate that the isomerization reaction proceeds through the potential surface of the singlet excited states.
- Sumitani, Minoru,Yoshihara, Keitaro
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- Stereoselective Hydrogenation of Alkynes, Enynes, and Dienes by Interlamellar Montmorillonite-Diphenylphosphinepalladium(II) Complex
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Stereoselective hydrogenation of alkynes, enynes, and dienes catalyzed by a heterogenized homogeneous catalyst, interlamellar montmorillonite-diphenylphosphinepalladium(II) anchored complex, has been reported. '
- Sharma, G. V. M.,Choudary, B. M.,Sarma, M. Ravichandra,Rao, K. Koteswara
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- Picosecond Laser Studies on Photochemical Reactions in Restricted Environments: The Photoisomerization of trans-Stilbene Complexed to Cyclodextrins
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The effect on picosecond reaction dynamics due to complexation of a reactive molecule with cyclodextrins was examined, with the trans-cis photoisomerization of stilbene as an example.In the presence of α-cyclodextrin, a single, slow exponential decay of trans-stilbene fluorescence is observed, consistent with the formation of a single complex.In contrast, in the presence of β-cyclodextrin, the fluorescence of trans-stilbene showed a clear double-exponential decay, consistent with the formation of two complexes.In the latter case, a dynamic equilibrium between a loose and a more tightly bound conformation of the complex is proposed, resulting in different photoisomerization reaction rates of trans-stilbene.
- Duveneck, Gert L.,Sitzmann, E. V.,Eisenthal, Kenneth B.,Turro, Nicholas J.
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- Physical chemistry of the lowest excited singlet state of trans-stilbene in solution as studied by time-resolved Raman spectroscopy
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Structure and dynamics of the lowest excited singlet state of trans-stilbene (the S1 state of tSB) in solution are discussed with an emphasis placed on the elucidation of the mechanism of the trans-cis photoisomerization. Structure of S1 tSB in solution is first discussed based on the time-resolved Raman spectral data and their isotope substitution effects. Original data for an asymmetrically deuteriated tSB, tSB-d5, are presented to confirm the ethylene-like structure of the central C-C linkage of S1 tSB. Next, the time-, temperature-, and solvent-dependent band shape changes of the olefinic C=C stretch band are discussed in terms of the solvent induced dynamic polarization. It is shown that the dynamic polarization model accounts very well, not only for the observed band shape changes, but also for their relevance to the isomerization mechanism. A new microscopic view on the photoisomerization of tSB is thus presented. Picosecond energy dissipation process of S1 tSB is then discussed in relation to the microscopic solvation structure in chloroform. Finally, the mechanism of a new bimolecular reaction between S1 tSB and carbon tetrachloride is discussed on the basis of the diffusion-controlled reaction model.
- Hamaguchi, Hiro-O,Iwata, Koichi
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- Alkyne- and Alkyl-tris(cyclopentadienyl) Complexes of Uranium(III)
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Treatment of cp3U(THF) (1) (cp = η-C5H5, THF = tetrahydrofuran) with diphenylacetylene affords the alkyne complex cp3U(Ph-CC-Ph); (1) reacts with RLi (R = Me, Bun) to give the alkyl compounds cp3URLi (3); hydrogenolysis of (3) in the presence of a terminal alkene R'(-H) leads to the formation of cp3UR'Li.
- Foyentin, Muriel,Folcher, Gerard,Ephritikhine, Michel
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- STEREOSPEZIFISCHE CARBONYLOLEFINIERUNG WAHLWEISE ZU EINEM (Z)- ODER (E)-OLEFIN MIT DEN REAGENZIEN IODO-TRIPHENYLSILYL- UND IODO-TRIPHENYLGERMYL-METHYLLITHIUM OHNE TRENNUNG DIASTEREOMERER ZWISCHENPRODUKTE (1)
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The recently found (1) stereospecific transformation of benzaldehyde by the reagents Ph3M-CH(I)Li (M= Si, Ge) to Ph3M-substituted oxiranes renders possible a method for olefination of benzaldehyde to give Z- or E-olefins, alternatively.This is demonstrated with two examples. - The synthesis of Ph3Sn-CH(I)Li is described.
- Kauffmann, Thomas,Koenig, Rolf,Kriegesmann, Reinhard,Wensing, Michael
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- Photochemical Trans Cis Isomerization of 1,2-Bis(hetroaryl)ethylenes: 1,2-Bis(pyrazinyl)ethylene
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The direct and sensitized trans (*) cis photoisomerization of 1,2-bis(pyrazinyl)ethylene is investigated in various conditions.Quantum yields of the direct trans -> cis photoisomerization increase with increasing solvent polarity because of the proximity of the lowest 1(n,?*) and 1(?,?*) states.Azulene quenches the direct and sensitized photoisomerization, giving the same Stern - Volmer constant indicating that the triplet state is the reactive state in both cases.The directly measured triplet lifetime of trans-1,2-bis(pyrazinyl)ethylene by laser spectroscopy is the same as the lifetime calculated from the azulene quenching studies.Laser spectroscopy also indicates efficient intersystem crossing following direct irradiation.From these results, it is concluded that the direct photoisomerization of 1,2-bis(pyrazinyl)ethylene proceeds through the triplet manifold in contrast to stilbene which undergoes direct trans (*) cis photoisomerization through the singlet manifold.
- Bong, Pill-Hoon,Kim, Hyeong Jin,Chae, Kyu Ho,Shim, Sang Chul,Nakashima, Nobuaki,Yoshihara, Keitaro
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- Influence of solvent viscosity on the photoisomerization of a novel trans-stilbene derivative with hindered single bond torsion
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Fluorescence life-time measurements were performed at elevated pressure and temperature to examine the viscosity dependence of the rate of photoinduced isomerization, kiso, in a stilbene derivative in which the single bond torsion is hindered by the introduction of CH2 bridges. The results obtained with n-hexane and methylcyclohexane as solvents (0.2 mPa siso=C·(η/mPa s)-a·exp(-EA/RT). The value for a drops from about 0.30 in n-hexane to about 0.15 in methylcyclohexane thus pointing to solvent specific contributions to the friction. The derived activation energies EA are about 12.8 and 12.5 kJ mol-1 in n-hexane and methylcyclohexane, respectively.
- Schneider,Brem,Jaeger,Rehaber,Lenoir,Frank
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- Photoinduced ene-reaction of 9-methylene-9,10-dihydrophenanthrene with alkenes
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Irradiation of 9-methylene-9,10-dihydrophenanthrene (1) in the presence of 1,1-diphenylethene or styrene in benzene afforded ene-reaction adduct in good yield. In the absence of arylalkenes, the dimerized product of 1, 9-[2-(9-phenanthryl)ethyl]-9,10-dihydrophenanthrene, and 9-methylphenanthrene were obtained as major products.
- Sugimoto, Akira,Hiraoka, Ryoichi,Yasueda, Masahiro Kanayama,Mukae, Hirofumi,Mizuno, Kazuhiko
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- Electrochemical Proton Reduction over Nickel Foam for Z-Stereoselective Semihydrogenation/deuteration of Functionalized Alkynes
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Selective reduction strategies based on abundant-metal catalysts are very important in the production of chemicals. In this paper, a method for the electrochemical semihydrogenation and semideuteration of alkynes to form Z-alkenes was developed, using a simple nickel foam as catalyst and H3O+ or D3O+ as sources of hydrogen or deuterium. Good yields and excellent stereoselectivities (Z/E up to 20 : 1) were obtained under very mild reaction conditions. The reaction proceeded with terminal and nonterminal alkynes, and also with alkynes containing easily reducible functional groups, such as carbonyl groups, as well as aryl chlorides, bromides, and even iodides. The nickel-foam electrocatalyst could be recycled up to 14 times without any change in its catalytic properties.
- Valiente, Alejandro,Martínez-Pardo, Pablo,Kaur, Gurpreet,Johansson, Magnus J.,Martín-Matute, Belén
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- Iodine promoted reduction of aromatic carbonyl compounds with phosphonic acid to access hydrocarbons
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A novel method for selective reduction of aromatic carbonyl compounds by phosphorus acid under metal-free conditions is achieved to produce the corresponding reduced products in good to excellent yields. By using H3PO3/I2 system, various aromatic ketones and aldehydes could be reduced to the corresponding hydrocarbons. Diketone compounds could also be reduced to the corresponding Z-alkenes. The protocol is low-cost and easily scaled up, which provides a simple and practical approach to access corresponding hydrocarbons.
- Deng, Jinfeng,Xiao, Jing,Wang, Xiaoyi,Luo, Huang,Jia, Zhicheng,Wang, Jie
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- Heterobimetallic Pd/Mn and Pd/Co complexes as efficient and stereoselective catalysts for sequential Cu-free Sonogashira coupling–alkyne semi-hydrogenation reactions
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A series of heterobimetallic PdII/MII complexes (MII = Mn, Co) were synthesised and tested as precatalysts for sequential Sonogashira coupling–alkyne semi-hydrogenation reactions to form Z-aryl alkenes. The carbometalated heterobimetallic PdII/CoII complex CoPdL3′ demonstrated an apparent cooperative effect compared to the corresponding monometallic counterparts. This compound was identified as a potent single-molecule catalyst for the one-pot Cu-free Sonogashira coupling of aryl bromides with terminal alkynes followed by chemo- and stereoselective semi-hydrogenation of the alkyne intermediate using NH3·BH3 as a hydrogen source. Furthermore, different aromatic substrates have been tested to show the generality of the reaction for the synthesis of Z-alkenes, including biologically active combretastatin A-4. In addition, the homogeneous nature of the catalytically active species was demonstrated.
- Baweja, Saral,Clauss, Reike,Gelman, Dmitri,Hey-Hawkins, Evamarie
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p. 1344 - 1356
(2022/02/03)
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- Energy-Transfer-Mediated Photocatalysis by a Bioinspired Organic Perylenephotosensitizer HiBRCP
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Energy transfer plays a special role in photocatalysis by utilizing the potential energy of the excited state through indirect excitation, in which a photosensitizer determines the thermodynamic feasibility of the reaction. Bioinspired by the energy-transfer ability of natural product cercosporin, here we developed a green and highly efficient organic photosensitizer HiBRCP (hexaisobutyryl reduced cercosporin) through structural modification of cercosporin. After structural manipulation, its triplet energy was greatly improved, and then, it could markedly promote the efficient geometrical isomerization of alkenes from the E-isomer to the Z-isomer. Moreover, it was also effective for energy-transfer-mediated organometallic catalysis, which allowed realization of the cross-coupling of aryl bromides and carboxylic acids through efficient energy transfer from HiBRCP to nickel complexes. Thus, the study on the relationship between structural manipulation and their photophysical properties provided guidance for further modification of cercosporin, which could be applied to more meaningful and challenging energy-transfer reactions.
- Zhang, Yan,Xia, Mingze,Li, Min,Ping, Qian,Yuan, Zhenbo,Liu, Xuanzhong,Yin, Huimin,Huang, Shuping,Rao, Yijian
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p. 15284 - 15297
(2021/11/01)
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- A Photorobust Mo(0) Complex Mimicking [Os(2,2′-bipyridine)3]2+and Its Application in Red-to-Blue Upconversion
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Osmium(II) polypyridines are a well-known class of complexes with luminescent metal-to-ligand charge-transfer (MLCT) excited states that are currently experiencing a revival due to their application potential in organic photoredox catalysis, triplet-triplet annihilation upconversion, and phototherapy. At the same time, there is increased interest in the development of photoactive complexes made from Earth-abundant rather than precious metals. Against this background, we present a homoleptic Mo(0) complex with a new diisocyanide ligand exhibiting different bite angles and a greater extent of π-conjugation than previously reported related chelates. This new design leads to deep red emission, which is unprecedented for homoleptic arylisocyanide complexes of group 6 metals. With a 3MLCT lifetime of 56 ns, an emission band maximum at 720 nm, and a photoluminescence quantum yield of 1.5% in deaerated toluene at room temperature, the photophysical properties are reminiscent of the prototypical [Os(2,2′-bipyridine)3]2+ complex. Under 635 nm irradiation with a cw-laser, the new Mo(0) complex sensitizes triplet-triplet annihilation upconversion of 9,10-diphenylanthracene (DPA), resulting in delayed blue fluorescence with an anti-Stokes shift of 0.93 eV. The photorobustness of the Mo(0) complex and the upconversion quantum yield are high enough to generate a flux of upconverted light that can serve as a sufficiently potent irradiation source for a blue-light-driven photoisomerization reaction. These findings are relevant in the greater contexts of designing new luminophores and photosensitizers for use in red-light-driven photocatalysis, photochemical upconversion, light-harvesting, and phototherapy.
- Bilger, Jakob B.,Kerzig, Christoph,Larsen, Christopher B.,Wenger, Oliver S.
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supporting information
p. 1651 - 1663
(2021/02/01)
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- Illuminatinganti-hydrozirconation: controlled geometric isomerization of an organometallic species
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A general strategy to enable the formalanti-hydrozirconation of arylacetylenes is reported that mergescis-hydrometallation using the Schwartz Reagent (Cp2ZrHCl) with a subsequent light-mediated geometric isomerization atλ= 400 nm. Mechanistic delineation of thecontra-thermodynamic isomerization step indicates that a minor reaction product functions as an efficientin situgenerated photocatalyst. Coupling of theE-vinyl zirconium species with an alkyne unit generates a conjugated diene: this has been leveraged as a selective energy transfer catalyst to enableE→Zisomerization of an organometallic species. Through anUmpolungmetal-halogen exchange process (Cl, Br, I), synthetically useful vinyl halides can be generated (up toZ?:?E= 90?:?10). This enabling platform provides a strategy to access nucleophilic and electrophilic alkene fragments in both geometric forms from simple arylacetylenes.
- Gilmour, Ryan,Hostmann, Theresa,Nevesely, Tomá?
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p. 10643 - 10648
(2021/08/20)
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- Manganese(i) complexes with metal-to-ligand charge transfer luminescence and photoreactivity
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Precious metal complexes with the d6 valence electron configuration often exhibit luminescent metal-to-ligand charge transfer (MLCT) excited states, which form the basis for many applications in lighting, sensing, solar cells and synthetic photochemistry. Iron(ii) has received much attention as a possible Earth-abundant alternative, but to date no iron(ii) complex has been reported to show MLCT emission upon continuous-wave excitation. Manganese(i) has the same electron configuration as that of iron(ii), but until now has typically been overlooked in the search for cheap MLCT luminophores. Here we report that isocyanide chelate ligands give access to air-stable manganese(i) complexes that exhibit MLCT luminescence in solution at room temperature. These compounds were successfully used as photosensitizers for energy- and electron-transfer reactions and were shown to promote the photoisomerization of trans-stilbene. The observable electron transfer photoreactivity occurred from the emissive MLCT state, whereas the triplet energy transfer photoreactivity originated from a ligand-centred 3π–π* state. [Figure not available: see fulltext.]
- H?ussinger, Daniel,Herr, Patrick,Kerzig, Christoph,Larsen, Christopher B.,Wenger, Oliver S.
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p. 956 - 962
(2021/08/09)
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- Efficient photocatalytic chemoselective and stereoselective C-C bond formation over AuPd@N-rich carbon nitride
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Heterogeneous chemoselective or stereoselective C-C coupling reactions remain extremely challenging in traditional organic synthesis. Here, we constructed a AuPd@N-rich carbon nitride (NRCN) photocatalyst through simple ammonia solution heat treatment of carbon nitride and then AuPd NP loading. AuPd@NRCN exhibited extraordinary light color promoted catalytic performance in C-C bond formation under visible light in air. Surprisingly, both high chemoselectivity to unsymmetrical Ullmann biaryl products and satisfactory stereoselectivity to Z-type Heck reaction products could be achieved by changing the light source color. Various substrates exhibited great potential for the economical synthesis of unsymmetrical biaryl products and Z-type olefins. Efficient visible light promoted C-I bond activation accompanied with improved photocatalytic coupling reaction efficiency over AuPd@NRCN was verified firstly by in situ DRIFTS. Considering that the Ullmann cross-coupling reaction is a multi-photon reaction, the improved photocatalytic performance in the Ullmann cross-coupling reaction using a combination of light sources with different colors might be due to the activation of different substrates and/or steps requiring different energies, and the combination of the two energy sources was beneficial for improving the activation efficiency of different substrates and/or steps. The activation of iodobenzene and styrene in the Heck reaction with light was also beneficial to the formation of the stilbene product. The light color promoted chemoselectivity and stereoselectivity are expected to have profound impact on organic synthetic methodology improvement. This journal is
- Jiang, Heyan,Xu, Jie,Zhang, Sishi,Cheng, Hongmei,Zang, Cuicui,Bian, Fengxia
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p. 219 - 229
(2021/01/28)
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- Synthesis of new adamantyl-imine palladium(II) complexes and their application in Mizoroki-Heck and Suzuki-Miyaura C[sbnd]C cross-coupling reactions
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Improving carbon–carbon cross-coupling reactions is an ongoing process and finding the most versatile and stable catalyst precursors has been of great interest. Ligand design has been proven to be important since it is responsible for providing electron density and steric saturation around the metal centre, thus contributing towards the stereo-electronic properties. The adamantyl moiety has been used to generate highly bulky and electron-rich ligands for application in palladium-catalysed cross-coupling reactions. Accordingly, we have prepared some Schiff-base adamantyl ligands (L1-L3) and complexed them with [PdCl2(MeCN)2] to afford the (pre)catalysts C1-C3, which were successfully applied in Mizoroki-Heck and Suzuki-Miyaura carbon–carbon cross-coupling reactions. The cross-coupling reaction products were obtained in good yields using 0.5 mol % Pd catalyst loading. C2 and C3 showed remarkable activity in the Mizoroki-Heck coupling reactions involving substrates with substituents on the olefin and aryl halide (including 4-Cl, 4-CH3, -CO2Me and -CO2Et). We also, observed that the Suzuki-Miyaura cross-coupling system was active towards challenging activated and deactivated aryl chlorides, with to up 70% conversions recorded. The mercury poisoning tests conducted revealed that the catalysts act as homogenous molecular active species in the Mizoroki-Heck reactions and act as both homogenous and heterogeneous catalysts in the Suzuki-Miyaura cross-coupling reactions.
- Makhubela, Banothile C. E.,Matsheku, Asanda C.,Maumela, Munaka C.
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- An Amine-Assisted Ionic Monohydride Mechanism Enables Selective Alkyne cis-Semihydrogenation with Ethanol: From Elementary Steps to Catalysis
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The selective synthesis of Z-alkenes in alkyne semihydrogenation relies on the reactivity difference of the catalysts toward the starting materials and the products. Here we report Z-selective semihydrogenation of alkynes with ethanol via a coordination-induced ionic monohydride mechanism. The EtOH-coordination-driven Cl- dissociation in a pincer Ir(III) hydridochloride complex (NCP)IrHCl (1) forms a cationic monohydride, [(NCP)IrH(EtOH)]+Cl-, that reacts selectively with alkynes over the corresponding Z-alkenes, thereby overcoming competing thermodynamically dominant alkene Z-E isomerization and overreduction. The challenge for establishing a catalytic cycle, however, lies in the alcoholysis step; the reaction of the alkyne insertion product (NCP)IrCl(vinyl) with EtOH does occur, but very slowly. Surprisingly, the alcoholysis does not proceed via direct protonolysis of the Ir-C(vinyl) bond. Instead, mechanistic data are consistent with an anion-involved alcoholysis pathway involving ionization of (NCP)IrCl(vinyl) via EtOH-for-Cl substitution and reversible protonation of Cl- ion with an Ir(III)-bound EtOH, followed by β-H elimination of the ethoxy ligand and C(vinyl)-H reductive elimination. The use of an amine is key to the monohydride mechanism by promoting the alcoholysis. The 1-amine-EtOH catalytic system exhibits an unprecedented level of substrate scope, generality, and compatibility, as demonstrated by Z-selective reduction of all alkyne classes, including challenging enynes and complex polyfunctionalized molecules. Comparison with a cationic monohydride complex bearing a noncoordinating BArF- ion elucidates the beneficial role of the Cl- ion in controlling the stereoselectivity, and comparison between 1-amine-EtOH and 1-NaOtBu-EtOH underscores the fact that this base variable, albeit in catalytic amounts, leads to different mechanisms and consequently different stereoselectivity.
- Huang, Zhidao,Wang, Yulei,Leng, Xuebing,Huang, Zheng
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supporting information
p. 4824 - 4836
(2021/04/07)
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- A simple and efficientin situgenerated copper nanocatalyst for stereoselective semihydrogenation of alkynes
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Development of a simple, effective, and practical method for (Z)-selective semihydrogenation of alkynes has been considered necessary for easy-to-access applications at organic laboratory scales. Herein, (Z)-selective semihydrogenation of alkynes was achieved using a copper nanocatalyst which was generatedin situsimply by adding ammonia borane to an ethanol solution of copper sulfate. Different types of alkynes including aryl-aryl, aryl-alkyl, and aliphatic alkynes were selectively reduced to (Z)-alkenes affording up to 99% isolated yield. The semihydrogenation of terminal alkynes to alkenes and gram-scale applications were also reported. In addition to eliminating catalyst preparation, the proposed approach is simple and practical and serves as a suitable alternative method to the conventional Lindlar catalyst.
- Park, Byoung Yong,Lim, Taeho,Han, Min Su
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supporting information
p. 6891 - 6894
(2021/07/19)
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- Copper(0) nanoparticle catalyzed Z-Selective Transfer Semihydrogenation of Internal Alkynes
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The use of copper(0) nanoparticles in the transfer semihydrogenation of alkynes has been investigated as a lead-free alternative to Lindlar catalysts. A stereo-selective methodology for the hydrogenation of internal alkynes to the corresponding (Z)-alkenes in high isolated yields (86% average) has been developed. This green and sustainable transfer hydrogenation protocol relies on non-noble copper nanoparticles for reduction of both electron-rich and electron-deficient, aliphatic-substituted and aromatic- substituted internal alkynes. Polyols, such as ethylene glycol and glycerol, have been proven to act as hydrogen sources, and excellent stereo- and chemoselectivity have been observed. Enabling technologies, such as microwave and ultrasound irradiation are shown to enhance heat and mass transfer, whether used alone or in combination, resulting in a decrease in reaction time from hours to minutes. (Figure presented.).
- Moran, Maria Jesus,Martina, Katia,Bieliunas, Vidmantas,Baricco, Francesca,Tagliapietra, Silvia,Berlier, Gloria,De Borggraeve, Wim M.,Cravotto, Giancarlo
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supporting information
p. 2850 - 2860
(2021/05/06)
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- Ligand-free (: Z)-selective transfer semihydrogenation of alkynes catalyzed by in situ generated oxidizable copper nanoparticles
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Herein, we present (Z)-selective transfer semihydrogenation of alkynes based on in situ generated CuNPs in the presence of hydrogen donors, such as ammonia-borane and a green protic solvent. This environmentally friendly method is characterized by operational simplicity combined with high stereo- and chemoselectivity and functional group compatibility. Auto-oxidation of CuNPs after the completion of a semihydrogenation reaction results in the formation of a water-soluble ammonia complex, so that the catalyst may be reused several times by simple phase-separation with no need for any special regeneration processes. Formed NH4B(OR)4 can be easily transformed back into ammonia-borane or into boric acid. In addition, a one-pot tandem sequence involving a Suzuki reaction followed by semihydrogenation was presented, which allows minimization of chemical waste production.
- Grela, Karol,Kusy, Rafa?
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supporting information
p. 5494 - 5502
(2021/08/16)
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- Palladium nanoparticlesin situsynthesized onCyclea barbatapectin as a heterogeneous catalyst for Heck coupling in water, the reduction of nitrophenols and alkynes
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This study develops an effective method for thein situsynthesis of palladium nanoparticles (PdNPs) usingCyclea barbatapectin as a green reducing and stabilizing reagent. The PdNP@pectin nanocomposite was well characterized by analysis techniques such as UV-vis, FTIR, EDX, XRD, SEM, HR-TEM and STEM-mapping. Crystalline PdNPs were found to be distributed in the size range of 1-25 nm with the highest frequency of 6-12 nm. PdNP@pectin exhibited excellent recyclable catalysis activity for the Heck coupling reaction in water medium. The kinetics and recyclability of nanoparticles were investigated for the catalytic reduction ofo-,m- andp-nitrophenol. The result showed a good catalysis efficiency with five successful recycles without compromising much. In particular, the nanocomposite was used as a catalyst for the conversion of alkynes intocis-alkenes with KOH/DMF as a hydrogenation source. The reaction was also utilized effectively for the synthesis of sex pheromones, includingPlutella xylostella((Z)-11-hexadecen-1-yl acetate) andCylas formicarius((Z)-3-dodecen-1-yl(E)-2-butenoate) with the total yields of 70% and 68%, respectively. Therefore, PdNPs supported onC. barbatapectin are promising catalysis materials for application in various fields.
- Le, Van-Dung,Le, T. Cam-Huong,Chau, Van-Trung,Le, T. Ngoc-Duyen,Dang, Chi-Hien,Vo, T. To-Nguyen,Nguyen, Trinh Duy,Nguyen, Thanh-Danh
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p. 4746 - 4755
(2021/03/22)
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- Water-hydrogen-supplying iridium catalytic alkyne semi-reduction selective synthesis method Process for trans-olefines
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The method comprises the following steps: DPPE, COD, a catalyst, water and alkyne are subjected to reduction reaction of alkyne in an organic solvent, and cis-olefin is generated by reaction under nitrogen protection. The ligand DPPE, the catalyst, the water and the alkyne are subjected to a reduction reaction of alkyne in an organic solvent, and a trans-olefin is generated by the reaction under nitrogen protection. The reactor for the reduction reaction is a sealed pressure-resistant reactor, the temperature of the reduction reaction is 100 - 130 °C, and the reduction reaction time is 20 - 48h. The amount of the catalyst used is 5 - 20% of the molar amount of alkyne, and the amount of water is 10 - 50 times of the molar amount of alkyne. The ligand is used in an amount 0.2 - 5 times the molar amount of catalyst. The catalyst system disclosed by the invention has extremely high chemical reaction and stereoselectivity, and cis or trans olefinic products can be synthesized at high yield. The catalytic system has strong universality on substrates, and alkynes containing various functional groups can efficiently carry out high-selectivity reduction reaction.
- -
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Paragraph 0082-0085
(2021/09/29)
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- Method for selectively synthesizing cis-trans-olefin by catalytic alkyne semi-reduction through water-hydrogen-supplying palladium
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The method comprises the following steps: TEOA, NaOAc, a catalyst, water and alkyne are subjected to a reduction reaction of alkyne in an organic solvent to react to form cis-olefin. Ligand t-Bu2 PCl, The catalyst, water and the alkyne are subjected to a reduction reaction of alkyne in an organic solvent to react to form a trans-olefin. The reactor for the reduction reaction is a sealed pressure-resistant reactor, the temperature of the reduction reaction is 120 - 150 °C, and the reduction reaction time is 20 - 40h. The amount of the catalyst used is 5 - 20% of the molar amount of alkyne, and the amount of water is 10 - 50 times of the molar amount of alkyne. The ligand is used in an amount 2-5 times the molar amount of catalyst. In the invention, the catalyst system has extremely high chemical reaction and stereoselectivity, and cis or trans olefinic products can be synthesized at high yield. The catalytic system has strong universality on substrates, and alkynes containing various functional groups can efficiently carry out high-selectivity reduction reaction.
- -
-
Paragraph 0075; 0088-0091
(2021/10/30)
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- Method for reducing alkyne into olefin by taking water as hydrogen source under catalysis of nickel
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The invention discloses a method for reducing alkyne into olefin by taking water as a hydrogen source under the catalysis of nickel, which comprises the following steps: placing alkyne in a solvent to react under the action of a nickel catalyst, a ligand, alkali, a boron reagent and a hydrogen source, and carrying out post-treatment to obtain olefin, and the hydrogen source is water. According to the invention, a cheap metal nickel catalyst is combined with a boron reagent to activate water, so that hydrogen transfer is realized, and the use of dangerous hydrogen is avoided. The method has good stereoselectivity, no excessive hydrogenation product alkane is generated, conditions are mild, the highest yield can reach 99%, and the method has good application prospects.
- -
-
Paragraph 0055-0058
(2021/06/26)
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- Ruthenium-Catalyzed E-Selective Partial Hydrogenation of Alkynes under Transfer-Hydrogenation Conditions using Paraformaldehyde as Hydrogen Source
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E-alkenes were synthesized with up to 100 % E/Z selectivity via ruthenium-catalyzed partial hydrogenation of different aliphatic and aromatic alkynes under transfer-hydrogenation conditions. Paraformaldehyde as a safe, cheap and easily available solid hydrogen carrier was used for the first time as hydrogen source in the presence of water for transfer-hydrogenation of alkynes. Optimization reactions showed the best results for the commercially available binuclear [Ru(p-cymene)Cl2]2 complex as pre-catalyst in combination with 2,2-bis(diphenylphosphino)-1,1-binaphthyl (BINAP) as ligand (1 : 1 ratio per Ru monomer to ligand). Mechanistic investigations showed that the origin of E-selectivity in this reaction is the fast Z to E isomerization of the formed alkenes. Mild reaction conditions plus the use of cheap, easily available and safe materials as well as simple setup and inexpensive catalyst turn this protocol into a feasible and promising stereo complementary procedure to the well-known Z-selective Lindlar reduction in late-stage syntheses. This procedure can also be used for the production of deuterated alkenes simply using d2-paraformaldehyde and D2O mixtures.
- Fetzer, Marcus N. A.,Tavakoli, Ghazal,Klein, Axel,Prechtl, Martin H. G.
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p. 1317 - 1325
(2021/02/11)
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- Cobalt Complexes of Bulky PNP Ligand: H2Activation and Catalytic Two-Electron Reactivity in Hydrogenation of Alkenes and Alkynes
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The reactivity of cobalt pincer complexes supported by the bulky tetramethylated PNP ligands Me4PNPR(R = iPr, tBu) has been investigated. In these ligands, the undesired H atom loss reactivity observed earlier in some classical CH2-arm PNP cobalt complexes is blocked, allowing them to be utilized for promoting two-electron catalytic transformations at the cobalt center. Accordingly, reaction of the formally CoIMe complex 3 with H2 under ambient pressure and temperature afforded the CoIII trihydride 4-H, in a reaction cascade reasoned to proceed by two-electron oxidative addition and reductive eliminations. This mechanistic proposal, alongside the observance of alkene insertion and ethane production upon sequential exposure of 3 to ethylene and H2, prompted an exploration into 3 as a catalyst for hydrogenation. Complex 4-H, formed in situ from 3 under H2, was found to be active in the catalytic hydrogenation of alkenes and alkynes. The proposed two-electron mechanism is reminiscent of the platinum group metals and demonstrates the utility of the bulky redox-innocent Me4PNPR ligand in the avoidance of one-electron reactivity, a concept that may show broad applicability in expanding the scope of earth-abundant first-row transition-metal catalysis.
- Fayzullin, Robert R.,Gallagher, James M.,Khaskin, Eugene,Khusnutdinova, Julia R.,Lapointe, Sébastien,Osborne, James,Pandey, Dilip K.
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supporting information
p. 3617 - 3626
(2021/11/16)
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- Remarkable catalytic activity of polymeric membranes containing gel-trapped palladium nanoparticles for hydrogenation reactions
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Polymeric flat-sheet membranes and hollow fibers were prepared via UV photo-initiated polymerization of acrylic acid at the surface of commercial polyether sulfones (PES) membranes. These polymeric materials permitted to immobilize efficiently palladium nanoparticles (PdNP), which exhibited a mean diameter in the range of 4?6 nm. These materials were synthesized by chemical reduction of Pd(II) precursors in the presence of the corresponding support. We successfully applied the as-prepared catalytic materials in hydrogenation reactions under continuous flow conditions. Flat sheet membranes were more active than hollow fibers due to the flow configuration and defavorable operating conditions. Actually, various functional groups (i.e. C[dbnd]C, C[tbnd]C and NO2) were reduced in flow-through configuration, under mild conditions (between 1.4 and 2.2 bar H2 at 60 °C, using 3.2 mol% of Pd loading), archiving high conversions in short reaction times (12?24 s).
- López-Viveros, Melissa,Favier, Isabelle,Gómez, Montserrat,Lahitte, Jean-Fran?ois,Remigy, Jean-Christophe
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p. 263 - 269
(2020/05/13)
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- Introducing the Dihydro-1,3-azaboroles: Convenient Entry by a Three-Component Reaction, Synthetic and Photophysical Application
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The (Fmes)BH2·SMe2 reagent (7) reacts sequentially with an acetylene and, e.g., xylylisonitrile in a convenient three-component reaction to give a series of unprecedented dihydro-1,3-azaborole derivatives 16. The tolane-derived example 16a was deprotonated and used as a ligand in organometallic chemistry. Compounds 16 served as the starting materials for the straightforward synthesis of various dihydro-1,3-azaborinine derivatives by treatment with an isonitrile. Several diaryldihydro-1,3-azaboroles showed interesting photophysical properties such as aggregation-induced emission and high fluorescence quantum yields.
- Li, Jun,Daniliuc, Constantin G.,Kartha, Kalathil K.,Fernández, Gustavo,Kehr, Gerald,Erker, Gerhard
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supporting information
p. 2059 - 2067
(2021/02/06)
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- A Colorimetric Method for Quantifying Cis and Trans Alkenes Using an Indicator Displacement Assay
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A colorimetric indicator displacement assay (IDA) amenable to high-throughput experimentation was developed to determine the percentage of cis and trans alkenes. Using 96-well plates two steps are performed: a reaction plate for dihydroxylation of the alkenes followed by an IDA screening plate consisting of an indicator and a boronic acid. The dihydroxylation generates either erythro or threo vicinal diols from cis or trans alkenes, depending upon their syn- or anti-addition mechanisms. Threo diols preferentially associate with the boronic acid due to the creation of more stable boronate esters, thus displacing the indicator to a greater extent. The generality of the protocol was demonstrated using seven sets of cis and trans alkenes. Blind mixtures of cis and trans alkenes were made, resulting in an average error of ±2 % in the percentage of cis or trans alkenes, and implementing E2 and Wittig reactions gave errors of ±3 %. Furthermore, we developed variants of the IDA for which the color may be tuned to optimize the response for the human eye.
- Valenzuela, Stephanie A.,Crory, Hannah S. N.,Yao, Chao-Yi,Howard, James R.,Saucedo, Gabriel,de Silva, A. Prasanna,Anslyn, Eric V.
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supporting information
p. 13819 - 13823
(2021/05/17)
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- Clean protocol for deoxygenation of epoxides to alkenes: Via catalytic hydrogenation using gold
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The epoxidation of olefin as a strategy to protect carbon-carbon double bonds is a well-known procedure in organic synthesis, however the reverse reaction, deprotection/deoxygenation of epoxides is much less developed, despite its potential utility for the synthesis of substituted olefins. Here, we disclose a clean protocol for the selective deprotection of epoxides, by combining commercially available organophosphorus ligands and gold nanoparticles (Au NP). Besides being successfully applied in the deoxygenation of epoxides, the discovered catalytic system also enables the selective reduction N-oxides and sulfoxides using molecular hydrogen as reductant. The Au NP catalyst combined with triethylphosphite P(OEt)3 is remarkably more reactive than solely Au NPs. The method is not only a complementary Au-catalyzed reductive reaction under mild conditions, but also an effective procedure for selective reductions of a wide range of valuable molecules that would be either synthetically inconvenient or even difficult to access by alternative synthetic protocols or by using classical transition metal catalysts. This journal is
- Fiorio, Jhonatan L.,Rossi, Liane M.
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p. 312 - 318
(2021/01/29)
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- Mild and efficient desulfurization of thiiranes with MoCl5/Zn system
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Desulfurization of a variety of thiiranes to alkenes occurs chemoselectively in high yields upon treatment with MoCl5/Zn system under mild conditions. The new methodology demonstrates high functional group tolerance toward chloro, bromo, fluoro, methoxy, ester, ether and keto groups.
- Lee, Yeong Jin,Shin, Jeong Won,Yoo, Byung Woo
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- Wittig Olefination Using Phosphonium Ion-Pair Reagents Incorporating an Endogenous Base
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Despite common perception, the use of strong bases in Wittig chemistry is utterly unnecessary: we report a series of novel ion-pair phosphonium carboxylate reagents which are essentially "storable ylides". These reagents are straightforwardly prepared in excellent yields, and their fluxional nature permits clean olefination of a broad range of aldehydes and even hemiacetals.
- Vetter, Anna C.,Gilheany, Declan G.,Nikitin, Kirill
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p. 1457 - 1462
(2021/03/08)
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- A Solid-Phase Assisted Flow Approach to In Situ Wittig-Type Olefination Coupling
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Described herein is the development of a continuous flow, solid-phase triphenylphosphine (PS-PPh3) assisted protocol to facilitate the in situ coupling of reciprocal pairs of halogen and carbonyl functionalised molecular pairs by a Wittig olefination within 15 mins. The protocol entails injecting a single solution (1 : 1 CHCl3 : EtOH) containing the halogenated and carbonyl-based substrates into a continuously flowing stream of CHCl3 : EtOH (1 : 1), passed through a fixed bed of K2CO3 and PS-PPh3. With advancement to the previous PS-PPh3 coupling procedures, the method employs a traditional polystyrene-based immobilisation matrix, the substrate scope of the protocol extended to substituted ketones, secondary alkyl chlorides, and an unprotected maleimide scaffold.
- Aldrich-Wright, Janice R.,Dankers, Christian,Gordon, Christopher P.,Polyzos, Anastasios,Tadros, Joseph
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supporting information
p. 4184 - 4194
(2021/08/24)
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- Selective Construction of C?C and C=C Bonds by Manganese Catalyzed Coupling of Alcohols with Phosphorus Ylides
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Herein, we report the manganese catalyzed coupling of alcohols with phosphorus ylides. The selectivity in the coupling of primary alcohols with phosphorus ylides to form carbon-carbon single (C?C) and carbon-carbon double (C=C) bonds can be controlled by the ligands. In the conversion of more challenging secondary alcohols with phosphorus ylides the selectivity towards the formation of C?C vs. C=C bonds can be controlled by the reaction conditions, namely the amount of base. The scope and limitations of the coupling reactions were thoroughly evaluated by the conversion of 21 alcohols and 15 ylides. Notably, compared to existing methods, which are based on precious metal complexes as catalysts, the present catalytic system is based on earth abundant manganese catalysts. The reaction can also be performed in a sequential one-pot reaction generating the phosphorus ylide in situ followed manganese catalyzed C?C and C=C bond formation. Mechanistic studies suggest that the C?C bond was generated via a borrowing hydrogen pathway and the C=C bond formation followed an acceptorless dehydrogenative coupling pathway. (Figure presented.).
- Liu, Xin,Werner, Thomas
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supporting information
p. 1096 - 1104
(2020/12/31)
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- Ready approach to poly(vinyldiphenylphosphine): A novel soluble polymer for conveniently conducting Wittig reactions
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The novel poly(vinyldiphenylphosphine) could be easily prepared by using the reactions of the cheap poly(vinyl chloride) with sodium phosphides. Poly(vinyldiphenylphosphine) is soluble in common solvents while its corresponding phosphine oxide is hardly soluble in the solvents. Taking advantage of this different solubility, poly(vinyldiphenylphosphine) could be used as a soluble phosphinopolymer for the Wittig reactions. The reactions could take place efficiently to produce the corresponding olefins while the isolation of the products were simple since the resulted poly(vinyldiphenylphosphine oxide) was not soluble in the solvent and could be easily removed by filtration.
- Ye, Jing-Jing,Han, Li-Biao
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supporting information
(2021/01/25)
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- Rhodium-Catalyzed Regioselective Hydroformylation of Alkynes to α,β-Unsaturated Aldehydes Using Formic Acid
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A rhodium-catalyzed hydroformylation of alkynes with formic acid was developed. The method provides α,β-unsaturated aldehydes in high yield and E-selectivity without the need to handle toxic CO gas.
- Fan, Chao,Hou, Jing,Chen, Yu-Jia,Ding, Kui-Ling,Zhou, Qi-Lin
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supporting information
p. 2074 - 2077
(2021/04/05)
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- Pyrimidopteridine-Catalyzed Hydroamination of Stilbenes with Primary Amines: A Dual Photoredox and Hydrogen Atom Transfer Catalyst
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The applicability of a heteroaromatic photoredox catalyst in an additive-free photo-mediated hydroamination of stilbenes is described. Initiated by the excitation of a highly potent organic pyrimidopteridine photoredox catalyst (E?[PrPPT?/PrPPT·-] = +2.10 V vs SCE in MeCN), the photo-mediated hydroamination of stilbenes was enabled using unprotected, primary aliphatic, allylic, benzylic amines for the synthesis of various α-phenyl phenethylamine derivatives. Notably, the stereogenic center of α-chiral amines was fully preserved. Both starting materials serve as competent quenching partners. Fluorescence- and competitive fluorescence-quenching experiments as well as electron paramagnetic resonance spectroscopic analysis and density functional theory calculations allowed a plausible reaction mechanism to be deduced.
- Taeufer, Tobias,Hauptmann, Richy,El-Hage, Firas,Mayer, Thea S.,Jiao, Haijun,Rabeah, Jabor,Pospech, Jola
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p. 4862 - 4869
(2021/05/04)
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- Aza-peterson olefinations: Rapid synthesis of (E)-alkenes
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An aza-Peterson olefination methodology to access 1,3-dienes and stilbene derivatives from the corresponding allyl- or benzyltrimethylsilane is described. Silanes can be deprotonated using Schlosser's base and added to N -phenyl imines or ketones to directly give the desired products in high yields.
- Britten, Thomas K.,Basson, Ashley J.,Roberts, Dean D.,McLaughlin, Mark G.
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p. 3535 - 3544
(2021/06/03)
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- Electro-mediated PhotoRedox Catalysis for Selective C(sp3)–O Cleavages of Phosphinated Alcohols to Carbanions
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We report a novel example of electro-mediated photoredox catalysis (e-PRC) in the reductive cleavage of C(sp3)?O bonds of phosphinated alcohols to alkyl carbanions. As well as deoxygenations, olefinations are reported which are E-selective and can be made Z-selective in a tandem reduction/photosensitization process where both steps are photoelectrochemically promoted. Spectroscopy, computation, and catalyst structural variations reveal that our new naphthalene monoimide-type catalyst allows for an intimate dispersive precomplexation of its radical anion form with the phosphinate substrate, facilitating a reactivity-determining C(sp3)?O cleavage. Surprisingly and in contrast to previously reported photoexcited radical anion chemistries, our conditions tolerate aryl chlorides/bromides and do not give rise to Birch-type reductions.
- Barham, Joshua P.,K?nig, Burkhard,Karl, Tobias A.,Reiter, Sebastian,Tian, Xianhai,Yakubov, Shahboz,de Vivie-Riedle, Regina
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p. 20817 - 20825
(2021/08/18)
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- Boosting free radical type photocatalysis over Pd/Fe-MOFs by coordination structure engineering
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The development of novel heterogeneous photocatalytic systems, along with a deep understanding of the relationship between the catalytic center chemical environment and the catalytic performance, is of great significance. Herein, the surface microenvironment of Pd nanoparticles was modulated with engineered Fe-MOF coordination structures (octahedron MIL-100(Fe), concave octahedron MIL-101(Fe) and irregular lumpy MIL-53(Fe)). Two heterogeneous free radical photocatalytic organic transformations have been developed over Pd nanoparticle loaded Fe-MOFs (Pd/Fe-MOFs). The photocatalytic C-H arylation of thiazole and decarboxylation cross-coupling with cinnamic acid were investigated. Thiazole C-H arylation with halobenzenes was brought about through C-halogen bond activation with the photogenerated electron-rich Pd NPs, the aryl radical generation and the follow-up radical addition. The cinnamic acid decarboxylation cross-coupling was also achieved by means of C-halogen bond activation with photogenerated electron-rich Pd NPs. The base regulated the product stereoselectivity by affecting the balance between cinnamic acid and carboxylate anions, as well as the balance between aryl radicals and the coordination complex intermediates. The improvement of the heterogeneous photocatalytic performance for thiazole C-H arylation and cinnamic acid decarboxylation cross-coupling should be ascribed to the difference in the electron transfer efficiency to Pd NPs over various engineered Fe-O cluster coordination structures. This work highlights the importance of exploiting structure engineering for heterogeneous photocatalytic systems.
- Bian, Fengxia,Cheng, Hongmei,Dong, Fan,Jiang, Heyan,Jiang, Yanke,Yang, Lin,Zang, Cuicui
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p. 5543 - 5552
(2021/08/25)
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- Photocatalyst-free visible light promoted: E → Z isomerization of alkenes
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A simple and green method of visible light driven photocatalytic E to Z isomerization of alkenes has been developed. A variety of (Z)-alkenes can be prepared in the presence of visible light, without any additional photocatalyst. This protocol features photocatalyst-free conditions, which are mild, tolerant, and operationally simple, and is easy to implement.
- Xu, Jianbin,Liu, Na,Lv, Haiping,He, Chixian,Liu, Zining,Shen, Xianfu,Cheng, Feixiang,Fan, Baomin
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supporting information
p. 2739 - 2743
(2020/06/17)
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- cis-Selective Transfer Semihydrogenation of Alkynes by Merging Visible-Light Catalysis with Cobalt Catalysis
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Herein, the first example of visible-light-driven, cobalt-catalyzed transfer semihydrogenation of alkynes to alkenes is reported. It is carried out by using Ir[dF(CF3)ppy]2(dtbbpy)]PF6 as photosensitizer, CoBr2/n-Bu3P as proton-reducing catalyst, and i-Pr2NEt/AcOH as the hydrogen source. Under the established catalytic system, the semihydrogenation proceeds with Z as the major selectivity and with inhibition of over-reduction. Under mild reaction conditions, both internal and terminal alkynes, as well as reducible functional groups such as halogen, cyano, and ester, are tolerated. Preliminary mechanistic studies revealed the dual role of the photosensitizer in initiating the reaction via a single-electron transfer process and controlling the stereoselectivity via an energy transfer process. (Figure presented.).
- Ding, Hai-Xin,Guo, Wen-Jie,He, Yong-Qin,Song, Xian-Rong,Tian, Wan-Fa,Xiao, Qiang,Ye, Jing
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- Photophysical Properties of Silyl-Substituted Stilbene Derivatives
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The effects of silyl groups on the structural, absorption, fluorescence, and photoisomerization properties of stilbenes were investigated. In comparison to that of the parent stilbene (1), fluorescence quantum yields (Φf) of Me3Si-substituted stilbenes 2–4 and 6 in solution were higher. Derivative 5, in which Me3Si groups are present at all ortho positions of the arene moieties, did not fluoresce at room temperature. The absorption and fluorescence wavelength maxima of Me3SiMe2Si-substituted stilbene 7 occurred at longer wavelengths compared to those of the Me3Si analog 2. The results of theoretical calculations showed that this difference is a consequence of an increase in the HOMO energy of 7 caused by orbital interaction between π-system and the σ(Si–Si) orbital. Stilbene 14, with two Me3Si-C≡C groups at both para positions, had a high Φf (0.95). The calculated transition dipole moment (μ) was well correlated with Φf. Derivative 21, which contains Ph2N and Me3SiC≡C groups exhibited solvatofluorochromism because it possesses a twisted intramolecular charge transfer (TICT) excited state in which the Ph2N group and the aromatic ring are orthogonal.
- Maeda, Hajime,Horikoshi, Ryo,Yamaji, Minoru,Furuyama, Taniyuki,Segi, Masahito
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p. 3410 - 3422
(2020/06/17)
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- Stereoselective Rhodium-Catalyzed Isomerization of Stereoisomeric Mixtures of Arylalkenes
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A new efficient method for the synthesis of a high ratio of E -alkenes from E / Z mixtures of alkenes with B 2pin 2in the presence of a rhodium catalyst is described. This reaction features mild reaction conditions, broad functional group tolerance, and highly great application potential.
- Yang, Hongxuan,Dong, Wenke,Wang, Wencan,Li, Tao,Zhao, Wanxiang
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p. 2833 - 2840
(2020/10/06)
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- Rare-Earth Supported Nickel Catalysts for Alkyne Semihydrogenation: Chemo- And Regioselectivity Impacted by the Lewis Acidity and Size of the Support
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Bimetallic catalysts of nickel(0) with a trivalent rare-earth ion or Ga(III), NiML3 (where L is [iPr2PCH2NPh]-, and M is Sc, Y, La, Lu, or Ga), were investigated for the selective hydrogenation of diphenylacetylene (DPA) to (E)-stilbene. Each bimetallic complex features a relatively short Ni-M bond length, ranging from 2.3395(8) ? (Ni-Ga) to 2.5732(4) ? (Ni-La). The anodic peak potentials of the NiML3 complexes vary from -0.48 V to -1.23 V, where the potentials are negatively correlated with the Lewis acidity of the M(III) ion. Three catalysts, Ni-Y, Ni-Lu, and Ni-Ga, showed nearly quantitative conversions in the semihydrogenation of DPA, with NiYL3 giving the highest selectivity for (E)-stilbene. Initial rate studies were performed on the two tandem catalytic reactions: DPA hydrogenation and (Z)-stilbene isomerization. The catalytic activity in DPA hydrogenation follows the order Ni-Ga > Ni-La > Ni-Y > Ni-Lu > Ni-Sc. The ranking of catalysts by (Z)-stilbene isomerization initial rates is Ni-Ga ? Ni-Sc > Ni-Lu > Ni-Y > Ni-La. In operando 31P and 1H NMR studies revealed that in the presence of DPA, the Ni bimetallic complexes supported by Y, Lu, and La form the Ni(η2-alkyne) intermediate, (η2-PhCCPh)Ni(iPr2PCH2NPh)2M(κ2-iPr2PCH2NPh). In contrast, the Ni-Ga resting state is the Ni(η2-H2) species, and Ni-Sc showed no detectable binding of either substrate. Hence, the mechanism of Ni-catalyzed diphenylacetylene semihydrogenation adheres to two different kinetics: an autotandem pathway (Ni-Ga, Ni-Sc) versus temporally separated tandem reactions (Ni-Y, Ni-Lu, Ni-La). Collectively, the experimental results demonstrate that modulating a base-metal center via a covalently appended Lewis acidic support is viable for promoting selective alkyne semihydrogenation.
- Ramirez, Bianca L.,Lu, Connie C.
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supporting information
p. 5396 - 5407
(2020/04/09)
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- Pd nanoparticles supported on reduced graphene oxide as an effective and reusable heterogeneous catalyst for the Mizoroki–Heck coupling reaction
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A general method for the synthesis of palladium nanoparticles loaded on reduced graphene oxide functionalized with diethylenetriamine (PdNPs/rGO-NH2) using a sonochemical procedure is described. The heterogeneous nanocomposite was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray, thermogravimetric analysis, high-angle annular dark field scanning transmission electron microscopy, X-ray photoelectron spectroscopy, UV–visible absorption, and inductively coupled plasma optical emission spectrometry. The PdNPs/rGO-NH2 was very effective for the Mizoroki–Heck coupling reaction of several aryl iodide compounds with different alkenes in the presence of triethylamine. The reaction provides the coupling products in good to excellent yields (59–100%). Additionally, the PdNPs/rGO-NH2 catalyst can be reutilized for six successive runs without any apparent diminution of its catalytic reactivity.
- Mirza-Aghayan, Maryam,Mohammadi, Marzieh,Addad, Ahmed,Boukherroub, Rabah
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- Ultrafine Pd nanoparticles loaded benzothiazole-linked covalent organic framework for efficient photocatalytic C-C cross-coupling reactions
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We proposed a strategy that a benzothiazole-linked covalent organic framework (TTT-COF) was used as a substrate to prepare metal composite photocatalyst Pd NPs?TTT-COF. Firstly, benzothiazole linked TTT-COF exhibited superior chemical stability and photoresponse. Moreover, a finer particle size (2.01 nm) and more uniform distribution of Pd NPs were observed in Pd NPs?TTT-COF owing to the binding interaction between Pd NPs and S in benzothiazole groups. Pd NPs?TTT-COF exhibited superior efficiency and reusability in photocatalytic C-C cross-coupling reactions. Mechanism study suggested that photogenerated electrons and holes on TTT-COF played important roles in these reactions. This journal is
- Cai, Yaqi,Niu, Hongyun,Xu, Lin,Yang, Yongliang,Zhang, Hui,Zhao, Weijia
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p. 29402 - 29407
(2020/10/02)
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- Efficient in situ palladium nano catalysis for Z-selective semi transfer hydrogenation of internal alkynes using safer 1, 4-butanediol
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Simple and efficient in situ generated palladium nanoparticles (PdNPs) in PEG-4OO catalyzed semi transfer hydrogenation of internal alkynes to Z-alkenes with excellent selectivity along with the formation of beneficial γ-butyrolactone as a byproduct using low quantity of safer and attractive 1, 4-butanediol as a hydrogen source was described.
- Rapeti, Siva Kumar,Kasina, Krishna Chaitanya,Gundepaka, Prasad,Birudaraju, Saritha,Sailaja
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supporting information
(2019/12/09)
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- Novel nickel nanoparticles stabilized by imidazolium-amidinate ligands for selective hydrogenation of alkynes
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The main challenge in the hydrogenation of alkynes into (E)- or (Z)-alkenes is to control the selective formation of the alkene, avoiding the over-reduction to the corresponding alkane. In addition, the preparation of recoverable and reusable catalysts is of high interest. In this work, we report novel nickel nanoparticles (Ni NPs) stabilized by three different imidazolium-amidinate ligands (ICy·(Ar)NCN; L1: Ar = p-tol, L2: Ar = p-anisyl and L3: Ar = p-ClC6H4). The as-prepared Ni NPs were fully characterized by (HR)-TEM, XRD, WASX, XPS and VSM. The nanocatalysts are active in the hydrogenation of various substrates. They present a remarkable selectivity in the hydrogenation of alkynes towards (Z)-alkenes, particularly in the hydrogenation of 3-hexyne into (Z)-3-hexene under mild reaction conditions (room temperature, 3% mol Ni and 1 bar H2). The catalytic behaviour of Ni NPs was influenced by the electron donor/acceptor groups (-Me, -OMe, -Cl) in the N-aryl substituents of the amidinate moiety of the ligands. Due to the magnetic character of the Ni NPs, recycling experiments were successfully performed after decantation in the presence of an external magnet, which allowed us to recover and reuse these catalysts at least 3 times preserving both activity and chemoselectivity.
- López-Vinasco, Angela M.,Martínez-Prieto, Luis M.,Asensio, Juan M.,Lecante, Pierre,Chaudret, Bruno,Cámpora, Juan,Van Leeuwen, Piet W. N. M.
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p. 342 - 350
(2020/02/04)
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- Ruthenium-Catalyzed E-Selective Alkyne Semihydrogenation with Alcohols as Hydrogen Donors
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Selective direct ruthenium-catalyzed semihydrogenation of diaryl alkynes to the corresponding E-alkenes has been achieved using alcohols as the hydrogen source. The method employs a simple ruthenium catalyst, does not require external ligands, and affords the desired products in > 99% NMR yield in most cases (up to 93% isolated yield). Best results were obtained using benzyl alcohol as the hydrogen donor, although biorenewable alcohols such as furfuryl alcohol could also be applied. In addition, tandem semihydrogenation-alkylation reactions were demonstrated, with potential applications in the synthesis of resveratrol derivatives.
- Ekebergh, Andreas,Begon, Romain,Kann, Nina
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p. 2966 - 2975
(2020/03/04)
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- Methanol as the Hydrogen Source in the Selective Transfer Hydrogenation of Alkynes Enabled by a Manganese Pincer Complex
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The first base metal-catalyzed transfer hydrogenation of alkynes with methanol is described. An air and moisture stable manganese pincer complex catalyzes the reduction of a variety of different alkynes to the corresponding (Z)-olefins in high yields. The
- Sklyaruk, Jan,Zubar, Viktoriia,Borghs, Jannik C.,Rueping, Magnus
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supporting information
p. 6067 - 6071
(2020/08/28)
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- Migratory Hydrogenation of Terminal Alkynes by Base/Cobalt Relay Catalysis
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Migratory functionalization of alkenes has emerged as a powerful strategy to achieve functionalization at a distal position to the original reactive site on a hydrocarbon chain. However, an analogous protocol for alkyne substrates is yet to be developed. Herein, a base and cobalt relay catalytic process for the selective synthesis of (Z)-2-alkenes and conjugated E alkenes by migratory hydrogenation of terminal alkynes is disclosed. Mechanistic studies support a relay catalytic process involving a sequential base-catalyzed isomerization of terminal alkynes and cobalt-catalyzed hydrogenation of either 2-alkynes or conjugated diene intermediates. Notably, this practical non-noble metal catalytic system enables efficient control of the chemo-, regio-, and stereoselectivity of this transformation.
- Liu, Bingxue,Liu, Qiang,Liu, Xufang
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supporting information
p. 6750 - 6755
(2020/03/13)
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- Piperazine-promoted gold-catalyzed hydrogenation: The influence of capping ligands
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Gold nanoparticles (NPs) combined with Lewis bases, such as piperazine, were found to perform selective hydrogenation reactions via the heterolytic cleavage of H2. Since gold nanoparticles can be prepared by many different methodologies and using different capping ligands, in this study, we investigated the influence of capping ligands adsorbed on gold surfaces on the formation of the gold-ligand interface. Citrate (Citr), poly(vinyl alcohol) (PVA), polyvinylpyrrolidone (PVP), and oleylamine (Oley)-stabilized Au NPs were not activated by piperazine for the hydrogenation of alkynes, but the catalytic activity was greatly enhanced after removing the capping ligands from the gold surface by calcination at 400 °C and the subsequent adsorption of piperazine. Therefore, the capping ligand can limit the catalytic activity if not carefully removed, demonstrating the need of a cleaner surface for a ligand-metal cooperative effect in the activation of H2 for selective semihydrogenation of various alkynes under mild reaction conditions.
- Barbosa, Eduardo C. M.,Camargo, Pedro H. C.,Fiorio, Jhonatan L.,Hashmi, A. Stephen K.,Kikuchi, Danielle K.,Rossi, Liane M.,Rudolph, Matthias
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p. 1996 - 2003
(2020/04/22)
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- Hydrogenation reaction method
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The invention relates to a hydrogenation reaction method, and belongs to the technical field of organic synthesis. The hydrogenation reaction method provided by the invention comprises the following steps: carrying out a hydrogen transfer reaction on a hydrogen acceptor compound, pinacol borane and a catalyst in a solvent in the presence of proton hydrogen, so that the hydrogen acceptor compound is subjected to a hydrogenation reaction; the catalyst is one or more than two of a palladium catalyst, an iridium catalyst and a rhodium catalyst; the hydrogen acceptor compound comprises one or morethan two functional groups of carbon-carbon double bonds, carbon-carbon triple bonds, carbon-oxygen double bonds, carbon-nitrogen double bonds, nitrogen-nitrogen double bonds, nitryl, carbon-nitrogentriple bonds and epoxy. The method is mild in reaction condition, easy to operate, high in yield, short in reaction time, wide in substrate application range, suitable for carbon-carbon double bonds,carbon-carbon triple bonds, carbon-oxygen double bonds, carbon-nitrogen double bonds, nitrogen-nitrogen double bonds, nitryl, carbon-nitrogen triple bonds and epoxy functional groups, good in selectivity and high in reaction specificity.
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Paragraph 0034; 0281-0284
(2020/05/14)
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- Generalized Chemoselective Transfer Hydrogenation/Hydrodeuteration
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A generalized, simple and efficient transfer hydrogenation of unsaturated bonds has been developed using HBPin and various proton reagents as hydrogen sources. The substrates, including alkenes, alkynes, aromatic heterocycles, aldehydes, ketones, imines, azo, nitro, epoxy and nitrile compounds, are all applied to this catalytic system. Various groups, which cannot survive under the Pd/C/H2 combination, are tolerated. The activity of the reactants was studied and the trends are as follows: styrene'diphenylmethanimine'benzaldehyde'azobenzene'nitrobenzene'quinoline'acetophenone'benzonitrile. Substrates bearing two or more different unsaturated bonds were also investigated and transfer hydrogenation occurred with excellent chemoselectivity. Nano-palladium catalyst in situ generated from Pd(OAc)2 and HBPin extremely improved the TH efficiency. Furthermore, chemoselective anti-Markovnikov hydrodeuteration of terminal aromatic olefins was achieved using D2O and HBPin via in situ HD generation and discrimination. (Figure presented.).
- Wang, Yong,Cao, Xinyi,Zhao, Leyao,Pi, Chao,Ji, Jingfei,Cui, Xiuling,Wu, Yangjie
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supporting information
p. 4119 - 4129
(2020/08/10)
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- Chemoselective semihydrogenation of alkynes catalyzed by manganese(i)-PNP pincer complexes
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A general manganese catalyzed chemoselective semihydrogenation of alkynes to olefins in the presence of molecular hydrogen is described. The best results are obtained by applying the aliphatic Mn PNP pincer complex Mn-3c which allows the transformation of various substituted internal alkynes to the respective Z-olefins under mild conditions and in high yields. Mechanistic investigations based on experiments and computations indicate the formation of the Z-isomer via an outer-sphere mechanism.
- Bachmann, Stephan,Beller, Matthias,Budweg, Svenja,Garbe, Marcel,Hornke, Helen,Jiao, Haijun,Junge, Kathrin,Papa, Veronica,Scalone, Michelangelo,Spannenberg, Anke,Wei, Zhihong
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p. 3994 - 4001
(2020/07/09)
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- Chemoselective Hydrogenation of Alkynes to (Z) -Alkenes Using an Air-Stable Base Metal Catalyst
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A highly selective hydrogenation of alkynes using an air-stable and readily available manganese catalyst has been achieved. The reaction proceeds under mild reaction conditions and tolerates various functional groups, resulting in (Z)-alkenes and allylic alcohols in high yields. Mechanistic experiments suggest that the reaction proceeds via a bifunctional activation involving metal-ligand cooperativity.
- Zubar, Viktoriia,Sklyaruk, Jan,Brzozowska, Aleksandra,Rueping, Magnus
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supporting information
p. 5423 - 5428
(2020/07/24)
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