- Correlating electronic and catalytic properties of frustrated Lewis pairs for imine hydrogenation
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Combined computational and experimental work to probe Lewis acidity of some boranes to be used in FLP hydrogenation. Gutmann-Beckett method of estimating Lewis acidity has limited capacity for sterically congested boranes. Calculated hydride affinity is a more appropriate tool for gauging Lewis acidity and correlate their FLP hydrogenation utility.
- Dorkó, éva,Kótai, Bianka,F?ldes, Tamás,Gy?m?re, ádám,Pápai, Imre,Soós, Tibor
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- A family of N-heterocyclic carbene-stabilized borenium ions for metal-free imine hydrogenation catalysis
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This manuscript probes the steric and electronic attributes that lead to "frustrated Lewis pair" (FLP)-type catalysis of imine hydrogenation by borenium ions. Hydride abstraction from (ItBu)HB(C6F5)2 2 prompts intramolecular C-H bond activation to give (CHN)2(tBu) (CMe2CH2)CB(C6F5)2 3, defining an upper limit of Lewis acidity for FLP hydrogenation catalysis. A series of seven N-heterocyclic carbene-borane (NHC-borane) adducts ((R′CNR)2C)(HBC8H14) (R′ = H, R = dipp 4a, Mes 5a, Me 8a; R = Me R′ = Me 9a, Cl, 10a) and ((HC)2(NMe)(NR)C)(HBC8H14) (R = tBu, 6a, Ph 7a) are prepared and converted to corresponding borenium salts. These species are evaluated as catalysts for metal-free imine hydrogenation at room temperature. Systematic tuning of the carbene donor for the hydrogenation of archetypal substrate N-benzylidene-tert-butylamine achieves the highest reported turn-over frequencies for FLP-catalyzed hydrogenation at amongst the lowest reported catalyst loadings. The most active NHC-borenium catalyst of this series, derived from 10a, is readily isolable, crystallographically characterized and shown to be effective in the hydrogenation catalysis of functional group-containing imines and N-heterocycles.
- Farrell, Jeffrey M.,Posaratnanathan, Roy T.,Stephan, Douglas W.
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- Synthesis of a diboryl-N-heterocycle and its conversion to a bidentate cationic Lewis acid
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Sequential reaction of 2-lithio-1-methylimidazole with 9-borabicyclo[3.3.1]nonane (9-BBN) dimer and 9-Cl-9-BBN yields diboryl-N-heterocycle C4H5N2(H)(BC8H14)2 (1). Reaction of 1 with I2 results in the net substitution of chelated hydride for a singly boron-bound iodide to produce C4H5N2(I)(BC8H14)2 (2). Conversely, reaction of 1 with [Ph3C][B(C6F5)4] results in the formation of the bidentate cationic Lewis acid [(C4H5N2)(BC8H14)2][B(C6F5)4] (3). Compound 3 catalyzes the hydrogenation of N-benzylidene-tert-butylamine at room-temperature.
- Farrell, Jeffrey M.,Stephan, Douglas W.
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- A rare olefin 1,1-carboboration reaction opens a synthetic pathway to an unusually structured frustrated Lewis pair
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(2,6-Dimesitylphenyl)P(vinyl)25d reacts with HB(C6F5)2 in a sequence involving a rare example of a 1,1-carboboration of an olefin to give the borylated tetrahydrophosphole derivative 6d. Compound 6d is an active frustrated Lewis pair that splits dihydrogen under mild conditions and serves as a metal-free hydrogenation catalyst. It also adds to carbon dioxide. Compound 6d serves as an intermediate in the HB(C6F5)2 catalyzed aryl(divinyl)phosphane (5d) to dihydrophosphole conversion. This journal is
- Chen, Chaohuang,Daniliuc, Constantin G.,Mück-Lichtenfeld, Christian,Kehr, Gerald,Erker, Gerhard
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- Reaction of carbon oxides with an ethylene-bridged PH/B Lewis pair
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The reaction of 2,4,6-tri(tert-butyl)phenyl vinyl phosphane with Piers’ borane [HB(C6F5)2] gave the ethylene-bridged PH/B frustrated Lewis pair (FLP) system. It is a monomer at high temperature (>323 K), but exists as an associated 12-membered macrocyclic trimer below 273 K. The PH/B FLP splits dihydrogen and serves as a metal-free hydrogenation catalyst. It adds carbon dioxide. It serves as a PH/B template for the reduction of carbon monoxide by the HB(C6F5)2borane to the formyl stage. The resulting six membered P/B/O containing heterocycle is opened upon treatment with pyridine and it reacts with benzaldehyde in a boron mediated Claisen-Tishchenko reaction.
- Sun, Qiu,Daniliuc, Constantin G.,Kehr, Gerald,Erker, Gerhard
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- A Highly Reactive Geminal P/B Frustrated Lewis Pair: Expanding the Scope to C-X (X=Cl, Br) Bond Activation
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The geminal frustrated Lewis pair tBu2PCH2B(Fxyl)2 (1; Fxyl=3,5-(CF3)2C6H3) is accessible in 65 % yield from tBu2PCH2Li and (Fxyl)2BF. According to NMR spectroscopy and X-ray crystallography, 1 is monomeric both in solution and in the solid state. The intramolecular P B distance of 2.900(5) ? and the full planarity of the borane site exclude any significant P/B interaction. Compound 1 readily activates a broad variety of substrates including H2, EtMe2SiH, CO2/CS2, Ph2CO, and H3CCN. Terminal alkynes react with heterolysis of the C-H bond. Haloboranes give cyclic adducts with strong P-BX3 and weak R3B-X bonds. Unprecedented transformations leading to zwitterionic XP/BCX3 adducts occur on treatment of 1 with CCl4 or CBr4 in Et2O. In less polar solvents (C6H6, n-pentane), XP/BCX3 adduct formation is accompanied by the generation of significant amounts of XP/BX adducts. FLP 1 catalyzes the hydrogenation of PhCH=NtBu and the hydrosilylation of Ph2CO with EtMe2SiH.
- Samigullin, Kamil,Georg, Isabelle,Bolte, Michael,Lerner, Hans-Wolfram,Wagner, Matthias
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- Iridium(III) Complexes Bearing Chelating Bis-NHC Ligands and Their Application in the Catalytic Reduction of Imines
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The IrIIIcomplexes 4 and 5 bearing bis-NHC ligands (NHC = N-heterocyclic carbene) composed of one classical NR,NR NHC and one N,NR NHC donor were prepared by the reaction of the azolium/azole compounds 2I and 3Br, respectively, with [{Cp*IrCl(μ-Cl)}2] (Cp=η5-C5Me5) in the presence of NaOAc as base. Most likely, the salts 2I and 3Br were first selectively deprotonated at the C2 position of the disubstituted (NR,NR) diazaheterocycle to generate an NHC donor, which then coordinated to the IrIIIcenter. Subsequently, NaOAc promoted C–H bond activation at the pendant imidazole moiety of the intermediate IrIIImono-NHC complexes led to the formation of the six-membered iridacycles 4 and 5, which bear a chelating, doubly C-metalated C(NHC)^C(NHC′) bis-NHC ligand. The IrIIIcomplexes 4 and 5 were tested as precatalysts for the reduction of imines with molecular hydrogen. Moderate to good activity was observed at a catalyst loading of 5 mol-% and an H2pressure of 3 bar in MeOH.
- Aznarez, Francisco,Iglesias, Manuel,Hepp, Alexander,Veit, Benjamin,Sanz Miguel, Pablo J.,Oro, Luis A.,Jin, Guo-Xin,Hahn, F. Ekkehardt
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- Autoinduced catalysis and inverse equilibrium isotope effect in the frustrated Lewis pair catalyzed hydrogenation of imines
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The frustrated Lewis pair (FLP)-catalyzed hydrogenation and deuteration of N-benzylidene-tert-butylamine (2) was kinetically investigated by using the three boranes B(C6F5)3 (1), B(2,4,6-F3-C6H2)3 (4), and B(2,6-F2-C6H3)3 (5) and the free activation energies for the H2 activation by FLP were determined. Reactions catalyzed by the weaker Lewis acids 4 and 5 displayed autoinductive catalysis arising from a higher free activation energy (2 kcal mol-1) for the H2 activation by the imine compared to the amine. Surprisingly, the imine reduction using D2 proceeded with higher rates. This phenomenon is unprecedented for FLP and resulted from a primary inverse equilibrium isotope effect. The FLP-catalyzed reaction of N-benzylidene-tert-butylamine with H2 and D2 was kinetically investigated. The free activation energy for the H2 activation by the FLP consisting of an imine and a less Lewis-acidic borane is 2 kcal mol-1 higher than for B(C6F5)3 , resulting in autoinduced catalysis. For the first time, the free activation enthalpies for the H2 activation by FLPs were experimentally determined and an inverse kinetic isotope effect was observed.
- Tussing, Sebastian,Greb, Lutz,Tamke, Sergej,Schirmer, Birgitta,Muhle-Goll, Claudia,Luy, Burkhard,Paradies, Jan
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- Influence of the lewis acidity of gallium atoms on the reactivity of a frustrated lewis pair: Experimental and theoretical studies
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The reactivity of the Ga/P-based frustrated Lewis pair (FLP) Mes2P-C[=C(H)-Ph]-GatBu2 (3) is influenced by the relatively weak Lewis acidity of its Ga atom and differs significantly from that of the analogous Al compound 1. The adduct of 3 with CO2 was only detectable at low temperature by NMR spectroscopy. Benzaldehyde was coordinated only via a Ga-O bond; the P atom was not involved. In contrast, a relatively persistent adduct was formed with soft CS2 to yield a five-membered GaCPCS heterocycle. Dehydrocoupling with H3B←NHMe2 afforded the dimeric amidoborane (H2B-NMe2)2, while an adduct with a GaCPBN heterocycle was isolated with the sterically less shielded ammonia-borane H3B←NH3. The latter product was unstable in solution and decomposed by H2 elimination and formation of oligomeric BN compounds. Small quantities of 3 catalyzed hydrogen transfer from H3B←NH3 to an imine. The Lewis acidities of the Al/P- and Ga/P-based FLPs were examined by experiments (Gutmann-Beckett method) and by calculation of the fluoride ion affinity (including the B and In analogues). The Al compound is the strongest Lewis acid; the Ga FLP is significantly weaker but is a stronger F- acceptor in comparison to the unknown analogues of B and In. These results reflect the different reactivities of these FLPs and may help to develop FLPs with finely adjusted properties.
- Possart, Josephine,Uhl, Werner
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- Selective Metal-free HB(C6F5)2Catalyzed Allene Cyclotrimerization: Formation of 1,3,5-Trimethylenecyclohexane and Its Tris-hydroboration Product
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Allene is cyclotrimerized under metal-free conditions with the borane HB(C6F5)2catalyst to selectively give 1,3,5-trimethylenecyclohexane (3 a). Three-fold hydroboration of the 1,3,5-cyclotrimer with Piers’ borane gives the all-cis 1,3,5-CH2B(C6F5)2substituted cyclohexane product 14.
- Tao, Xin,Kehr, Gerald,Daniliuc, Constantin G.,Erker, Gerhard
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- Continuous flow heterogeneous catalytic reductive aminations under aqueous micellar conditions enabled by an oscillatory plug flow reactor
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Despite the fact that continuous flow processing exhibits well-established technical advances, aqueous micellar chemistry, a field that has proven extremely useful in shifting organic synthesis to sustainable water-based media, has mostly been explored under conventional batch-based conditions. This is particularly because of the fact that the reliable handling of slurries and suspensions in flow has been considered as a significant technical challenge. Herein, we demonstrate that the strategic application of an oscillatory plug flow reactor enables heterogeneous catalytic reductive aminations in aqueous micellar media enhancing mass transport and facilitating process simplicity, stability and scalability. The micellar flow process enabled a broad range of substrates, including amino acid derivatives, to be successfully transformed under reasonably mild conditions utilizing only very low amounts of Pd/C as a readily available heterogeneous catalyst. The preparative capabilities of the process along with the recyclability of the heterogenous catalyst and the aqueous reaction media were also demonstrated. This journal is
- ?tv?s, Sándor B.,Buchholcz, Balázs,Darvas, Ferenc,Kappe, C. Oliver,Novák, Zoltán,Sipos, Gellért,Wernik, Michaela
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supporting information
p. 5625 - 5632
(2021/08/16)
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- Exploiting Continuous Processing for Challenging Diazo Transfer and Telescoped Copper-Catalyzed Asymmetric Transformations
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Generation and use of triflyl azide in flow enables efficient synthesis of a range of α-diazocarbonyl compounds, including α-diazoketones, α-diazoamides, and an α-diazosulfonyl ester, via both Regitz-type diazo transfer and deacylative/debenzoylative diazo-transfer processes with excellent yields and offers versatility in the solvent employed, in addition to addressing the hazards associated with handling of this highly reactive sulfonyl azide. Telescoping the generation of triflyl azide and diazo-transfer process with highly enantioselective copper-mediated intramolecular aromatic addition and C-H insertion processes demonstrates that the reaction stream containing the α-diazocarbonyl compound can be obtained in sufficient purity to pass directly over the immobilized copper bis(oxazoline) catalyst without detrimentally impacting the catalyst enantioselectivity.
- Crowley, Daniel C.,Brouder, Thomas A.,Kearney, Aoife M.,Lynch, Denis,Ford, Alan,Collins, Stuart G.,Maguire, Anita R.
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p. 13955 - 13982
(2021/09/02)
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- Imine reduction with me2s-bh3
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Although there exists a variety of different catalysts for hydroboration of organic substrates such as aldehydes, ketones, imines, nitriles etc., recent evidence suggests that tetra-coordinate borohydride species, formed by activation, redistribution, or decomposition of boron reagents, are the true hydride donors. We then proposed that Me2S-BH3 could also act as a hydride donor for the reduction of various imines, as similar compounds have been observed to reduce carbonyl substrates. This boron reagent was shown to be an effective and chemoselective hydroboration reagent for a wide variety of imines.
- Kamal, Mohammad M.,Liu, Zhizhou,Vidovi?, Dragoslav,Zhai, Siyuan
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- Implication of a Silyl Cobalt Dihydride Complex as a Useful Catalyst for the Hydrosilylation of Imines
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Here, we describe the formation and use of silyl cobalt (III) dihydride complexes as powerful catalysts for the hydrosilylation of a variety of imines starting from a low-valent well-defined cobalt (I) complex. The reaction is efficient at low catalyst loadings with a diverse range of imines bearing various protecting groups, as well as aliphatic ketimines and quinoline. Kinetics, DFT calculations, NMR spectroscopic studies, deuteration experiments, and X-ray diffraction analyses allowed us to propose a catalytic cycle based on silyl dihydrocobalt (III) complexes performing a hydrocobaltation.
- Barbazanges, Marion,Bories, Cassandre C.,Derat, Etienne,Petit, Marc
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p. 14262 - 14273
(2021/11/27)
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- Metallic Barium: A Versatile and Efficient Hydrogenation Catalyst
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Ba metal was activated by evaporation and cocondensation with heptane. This black powder is a highly active hydrogenation catalyst for the reduction of a variety of unactivated (non-conjugated) mono-, di- and tri-substituted alkenes, tetraphenylethylene, benzene, a number of polycyclic aromatic hydrocarbons, aldimines, ketimines and various pyridines. The performance of metallic Ba in hydrogenation catalysis tops that of the hitherto most active molecular group 2 metal catalysts. Depending on the substrate, two different catalytic cycles are proposed. A: a classical metal hydride cycle and B: the Ba metal cycle. The latter is proposed for substrates that are easily reduced by Ba0, that is, conjugated alkenes, alkynes, annulated rings, imines and pyridines. In addition, a mechanism in which Ba0 and BaH2 are both essential is discussed. DFT calculations on benzene hydrogenation with a simple model system (Ba/BaH2) confirm that the presence of metallic Ba has an accelerating effect.
- Stegner, Philipp,F?rber, Christian,Zenneck, Ulrich,Knüpfer, Christian,Eyselein, Jonathan,Wiesinger, Michael,Harder, Sjoerd
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supporting information
p. 4252 - 4258
(2020/12/22)
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- Cationic Aluminium Complexes as Catalysts for Imine Hydrogenation
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Strongly Lewis acidic cationic aluminium complexes, stabilized by β–diketiminate (BDI) ligands and free of Lewis bases, have been prepared as their B(C6F5)4? salts and were investigated for catalytic activity in imine hydrogenation. The backbone (R1) and N (R2) substituents on the R1,R2BDI ligand (R1,R2BDI=HC[C(R1)N(R2)]2) influence sterics and Lewis acidity. Ligand bulk increases along the row Me,DIPPBDIMe,DIPePBDI≈tBu,DIPPBDItBu,DIPePBDI; DIPP=2,6-C(H)Me2-phenyl, DIPeP=2,6-C(H)Et2-phenyl. The Gutmann-Beckett test showed acceptor numbers of: (tBu,DIPPBDI)AlMe+ 85.6, (tBu,DIPePBDI)AlMe+ 85.9, (Me,DIPPBDI)AlMe+ 89.7, (Me,DIPePBDI)AlMe+ 90.8, (Me,DIPPBDI)AlH+ 95.3. Steric and electronic factors need to be balanced for catalytic activity in imine hydrogenation. Open, highly Lewis acidic, cations strongly coordinate imine rendering it inactive as a Frustrated Lewis Pair (FLP). The bulkiest cations do not coordinate imine but its combination is also not an active catalyst. The cation (tBu,DIPPBDI)AlMe+ shows the best catalytic activity for various imines and is also an active catalyst for the Tishchenko reaction of benzaldehyde to benzylbenzoate. DFT calculations on the mechanism of imine hydrogenation catalysed by cationic Al complexes reveal two interconnected catalytic cycles operating in concert. Hydrogen is activated either by FLP reactivity of an Al???imine couple or, after formation of significant quantities of amine, by reaction with an Al???amine couple. The latter autocatalytic Al???amine cycle is energetically favoured.
- Friedrich, Alexander,Eyselein, Jonathan,Elsen, Holger,Langer, Jens,Pahl, Jürgen,Wiesinger, Michael,Harder, Sjoerd
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supporting information
p. 7756 - 7763
(2021/04/28)
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- Transition Metal-Free Direct Hydrogenation of Esters via a Frustrated Lewis Pair
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"Frustrated Lewis pairs"(FLPs) continue to exhibit unique reactivity for the reduction of organic substrates, yet to date, the catalytic hydrogenation of an ester functionality has not been demonstrated. Here, we report that iPr3SnNTf2 (1-NTf2; Tf = SO2CF3) is a more potent Lewis acid than the previously studied iPr3SnOTf; in an FLP with 2,4,6-collidine/2,6-lutidine (col/lut), this translates to faster H2 activation and the catalytic hydrogenolysis of an ester bond by a main-group compound, furnishing alcohol and ether (minor) products. The reaction outcome is sensitive to the steric and electronic properties of the substrate; CF3CO2Et and simple formates (HCO2Me and HCO2Et) are catalytically reduced, whereas related esters CF3CO2nBu and CH3CO2Et show only stoichiometric reactivity. A computational case study on the hydrogenation of CF3CO2Et and CH3CO2Et reveals that both share a common mechanistic pathway; however, key differences in the energies of a Sn-acetal intermediate and transition states emerge, favoring CF3CO2Et reduction. The alcohol products reversibly inhibit 1-NTf2/lut via formation of resting-state species 1-OR/[1·(1-OR)]+[NTf2]- however, the extra energy required to regenerate 1-NTf2/lut exacerbates the unfavorable reduction energy profile for CH3CO2Et, ultimately preventing turnover. These findings will assist the design of future main-group catalysts for ester hydrogenation, with improved performance.
- Sapsford, Joshua S.,Csókás, Dániel,Turnell-Ritson, Roland C.,Parkin, Liam A.,Crawford, Andrew D.,Pápai, Imre,Ashley, Andrew E.
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p. 9143 - 9150
(2021/07/31)
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- Heterometallic Mg?Ba Hydride Clusters in Hydrogenation Catalysis
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Reaction of a MgN“2/BaN”2 mixture (N“=N(SiMe3)2) with PhSiH3 gave three unique heterometallic Mg/Ba hydride clusters: Mg5Ba4H11N”7 ? (benzene)2 (1), Mg4Ba7H13N“9 ? (toluene)2 (2) and Mg7Ba12H26N”12 (3). Product formation is controlled by the Mg/Ba ratio and temperature. Crystal structures are described. While 3 is fully insoluble, clusters 1 and 2 retain their structures in aromatic solvents. DFT calculations and AIM analyses indicate highly ionic bonding with Mg?H and Ba?H bond paths. Also unusual H????H? bond paths are observed. Catalytic hydrogenation with MgN“2, BaN”2 and the mixture MgN“2/BaN”2 has been studied. Whereas MgN“2 is only active in imine hydrogenation, alkene and alkyne hydrogenation needs the presence of Ba. The catalytic activity of the MgN”2/BaN“2 mixture lies in general between that of its individual components and strong cooperative effects are not evident.
- Wiesinger, Michael,Knüpfer, Christian,Elsen, Holger,Mai, Jonathan,Langer, Jens,Harder, Sjoerd
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p. 4567 - 4577
(2021/09/09)
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- Cross dehydrogenative coupling strategy for allylation of benzylanilines promoted by DDQ
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A cross dehydrogenative coupling strategy for allylation of benzylanilines promoted by DDQ is reported, which uses nonmetallic quinone DDQ as an oxidant in the allylation of N-benzylanilines under mild conditions. C–C bond with high selectivity and activity was constructed in this reaction and homoallylic amines were obtained with yields of up to 99%.
- Xiong, Ruimei,Hussain, Muhammad Ijaz,Liu, Qing,Xia, Wen,Xiong, Yan
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supporting information
(2019/12/11)
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- Alkaline Earth Metal Aluminates as Catalysts for Imine Hydrogenation
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Alkaline earth (Ae) metal complexes with the alanate anion AlH4-have been prepared by salt metathesis between NaAlH4and AeCl2in THF and could be isolated as Mg(AlH4)2·(THF)4, Ca(AlH4)2·(THF)4, and Sr(AlH4)2·(THF)5. The previously reported crystal structure of the Mg alanate complex shows bonding of AlH4-with one bridging hydride, H3Al-(μ-H)-Mg, while the Ca and Sr alanates show a combination of H3Al-(μ-H)-Ae and H2Al-(μ-H)2-Ae bridging. The heteroleptic β-diketiminate complexes (DIPPBDI)Mg(AlH4)·THF and (DIPPBDI)Ca(AlH4)·(THF)2have been prepared by reaction of the corresponding Ae hydride complexes with AlH3·(THF)2[DIPPBDI = DIPP-NC(Me)C(H)C(Me)N-DIPP, where DIPP = 2,6-diisopropylphenyl]. Crystal structures show H2Al-(μ-H)2-Ae bridging. The Ca complex decomposes at room temperature by reduction of the β-diketiminate anion. Density functional theory calculations (B3PW91/def2tzvpp) show that the formation of Ae(AlH4)2from AeH2and AlH3is exothermic by δH (kilocalories per mole): Be, -68.8; Mg, -66.1; Ca, -95.4; Sr, -100.9; Ba, -112.3. Calculations of NPA charges on LiAlH4and the Ae alanate complexes (Ae = Mg, Ca, or Sr) show that these are highly ionic salts in which the charge on AlH4-of approximately -0.95 is hardly dependent on the countercation. Compared to LiAlH4, the Ae alanates are very efficient catalysts for imine hydrogenation, clearly extending the substrate scope. In addition to aldimines RC(H)=NR′ (R/R′ = Ph/tBu, tBu/tBu, nPr/tBu, or Ph/Ph), ketimine PhC(Me)=NtBu could be reduced. The salt [Bu4N+][AlH4-] is catalytically not active, which shows that the s-block metal is crucial. The highest activities were found for the heterobimetallic Ca and Sr alanates.
- Elsen, Holger,Langer, Jens,Wiesinger, Michael,Harder, Sjoerd
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supporting information
p. 4238 - 4246
(2020/06/04)
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- Efficient One-Pot Reductive Aminations of Carbonyl Compounds with Aquivion-Fe as a Recyclable Catalyst and Sodium Borohydride
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A one-pot reductive amination of aldehydes and ketones with NaBH4 was developed with a view to providing efficient, economical and greener synthetic conditions. A recyclable iron-based Lewis catalyst, Aquivion-Fe, was used to promote imine formation in cyclopentyl methyl ether, followed by the addition of a small amount of methanol to the reaction mixture to enable C=N reduction by NaBH4. The protocol, applied to a wide number of amines and carbonyl compounds, resulted in ever complete conversion of these latter with excellent chemoselectivity towards the expected amination products in the most cases. Isolated yields, determined for a selection of the screened substrates, were found consistent with the previously obtained conversion and selectivity data. Cinacalcet, an important active pharmaceutical ingredient, was efficiently prepared by the title procedure.
- Airoldi, Veronica,Piccolo, Oreste,Roda, Gabriella,Appiani, Rebecca,Bavo, Francesco,Tassini, Riccardo,Paganelli, Stefano,Arnoldi, Sebastiano,Pallavicini, Marco,Bolchi, Cristiano
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supporting information
p. 162 - 168
(2019/12/11)
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- Fast continuous alcohol amination employing a hydrogen borrowing protocol
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A continuous flow method for the direct conversion of alcohols to amines via a hydrogen borrowing approach is reported. The method utilises a low loading (0.5%) of a commercial catalyst system ([Ru(p-cymene)Cl2]2 and DPEPhos), reagent grade solvent and is selective for primary alcohols. Successful methylation of amines using methanol and the direct dimethylamination of alcohols using commercial dimethylamine solution are reported. The synthesis of two pharmaceutical agents Piribedil (5) and Buspirone (25) were accomplished in good yields employing these new methods.
- Labes, Ricardo,Mateos, Carlos,Battilocchio, Claudio,Chen, Yiding,Dingwall, Paul,Cumming, Graham R.,Rincón, Juan A.,Nieves-Remacha, Maria José,Ley, Steven V.
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supporting information
p. 59 - 63
(2019/01/11)
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- Regio- and Enantioselective Intramolecular Amide Carbene Insertion into Primary C-H Bonds Using Ru(II)-Pheox Catalyst
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We have established a method for the highly regio- and enantioselective functionalization of tert-butyl groups via intramolecular amide carbene insertion into C-H bonds, yielding γ-lactams with 91% ee in up to 99% yield. This reaction uses a ruthenium(II) phenyl oxazoline (Ru(II)-Pheox) complex. The catalytic intramolecular carbene transfer reaction to the primary C-H bond proceeds rapidly and selectively compared to that with secondary C-H, benzylic secondary C-H, tert-C-H, or sp2C-H bonds in the presence of 1 mol % Ru(II)-Pheox catalyst. This is the first example of a catalytic carbenoid insertion into an unactivated tert-butyl group with enantiocontrol at the carbenoid carbon.
- Nakagawa, Yoko,Chanthamath, Soda,Liang, Yumeng,Shibatomi, Kazutaka,Iwasa, Seiji
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p. 2607 - 2618
(2019/02/26)
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- Dual Role of Doubly Reduced Arylboranes as Dihydrogen- and Hydride-Transfer Catalysts
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Doubly reduced 9,10-dihydro-9,10-diboraanthracenes (DBAs) are introduced as catalysts for hydrogenation as well as hydride-transfer reactions. The required alkali metal salts M2[DBA] are readily accessible from the respective neutral DBAs and Li metal, Na metal, or KC8. In the first step, the ambiphilic M2[DBA] activate H2 in a concerted, metal-like fashion. The rates of H2 activation strongly depend on the B-bonded substituents and the counter cations. Smaller substituents (e.g., H, Me) are superior to bulkier groups (e.g., Et, pTol), and a Mes substituent is even prohibitively large. Li+ ions, which form persistent contact ion pairs with [DBA]2-, slow the H2-addition rate to a higher extent than more weakly coordinating Na+/K+ ions. For the hydrogenation of unsaturated compounds, we identified Li2[4] (Me substituents at boron) as the best performing catalyst; its substrate scope encompasses Ph(H)CNtBu, Ph2CCH2, and anthracene. The conversion of E-Cl to E-H bonds (E = C, Si, Ge, P) was best achieved by using Na2[4]. The latter protocol provides facile access also to Me2Si(H)Cl, a most important silicone building block. Whereas the H2-transfer reaction regenerates the dianion [4]2- and is thus immediately catalytic, the H--transfer process releases the neutral 4, which has to be recharged by Na metal before it can enter the cycle again. To avoid Wurtz-type coupling of the substrate, the reduction of 4 must be performed in the absence of the element halide, which demands an alternating process management (similar to the industrial anthraquinone process).
- Von Grotthuss, Esther,Prey, Sven E.,Bolte, Michael,Lerner, Hans-Wolfram,Wagner, Matthias
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supporting information
(2019/04/17)
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- Dual Role of Doubly Reduced Arylboranes as Dihydrogen- and Hydride-Transfer Catalysts
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Doubly reduced 9,10-dihydro-9,10-diboraanthracenes (DBAs) are introduced as catalysts for hydrogenation as well as hydride-transfer reactions. The required alkali metal salts M2[DBA] are readily accessible from the respective neutral DBAs and Li metal, Na metal, or KC8. In the first step, the ambiphilic M2[DBA] activate H2 in a concerted, metal-like fashion. The rates of H2 activation strongly depend on the B-bonded substituents and the counter cations. Smaller substituents (e.g., H, Me) are superior to bulkier groups (e.g., Et, pTol), and a Mes substituent is even prohibitively large. Li+ ions, which form persistent contact ion pairs with [DBA]2-, slow the H2-addition rate to a higher extent than more weakly coordinating Na+/K+ ions. For the hydrogenation of unsaturated compounds, we identified Li2[4] (Me substituents at boron) as the best performing catalyst; its substrate scope encompasses Ph(H)C=NtBu, Ph2C=CH2, and anthracene. The conversion of E-Cl to E-H bonds (E = C, Si, Ge, P) was best achieved by using Na2[4]. The latter protocol provides facile access also to Me2Si(H)Cl, a most important silicone building block. Whereas the H2-transfer reaction regenerates the dianion [4]2- and is thus immediately catalytic, the H--transfer process releases the neutral 4, which has to be recharged by Na metal before it can enter the cycle again. To avoid Wurtz-type coupling of the substrate, the reduction of 4 must be performed in the absence of the element halide, which demands an alternating process management (similar to the industrial anthraquinone process).
- Von Grotthuss, Esther,Prey, Sven E.,Bolte, Michael,Lerner, Hans-Wolfram,Wagner, Matthias
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supporting information
p. 6082 - 6091
(2019/04/17)
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- Aggregation Behavior of a Six-Membered Cyclic Frustrated Phosphane/Borane Lewis Pair: Formation of a Supramolecular Cyclooctameric Macrocyclic Ring System
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A new six-membered cyclic frustrated phosphane/borane Lewis pair was liberated from its HB(C6F5)2 adduct by treatment with vinylcyclohexane. The system is an active frustrated Lewis pair that undergoes cycloaddition reactions with suitable π reagents and it splits dihydrogen. At room temperature in solution the new compound is a monomer, however, in the crystal and in solution at low temperature it aggregates to a thermodynamically favoured supramolecular macrocyclic cyclooctamer.
- Jie, Xiaoming,Daniliuc, Constantin G.,Knitsch, Robert,Hansen, Michael Ryan,Eckert, Hellmut,Ehlert, Sebastian,Grimme, Stefan,Kehr, Gerald,Erker, Gerhard
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supporting information
p. 882 - 886
(2019/01/04)
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- Promoting Frustrated Lewis Pairs for Heterogeneous Chemoselective Hydrogenation via the Tailored Pore Environment within Metal–Organic Frameworks
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Frustrated Lewis pairs (FLPs) have recently been advanced as efficient metal-free catalysts for catalytic hydrogenation, but their performance in chemoselective hydrogenation, particularly in heterogeneous systems, has not yet been achieved. Herein, we demonstrate that, via tailoring the pore environment within metal–organic frameworks (MOFs), FLPs not only can be stabilized but also can develop interesting performance in the chemoselective hydrogenation of α,β-unsaturated organic compounds, which cannot be achieved with FLPs in a homogeneous system. Using hydrogen gas under moderate pressure, the FLP anchored within a MOF that features open metal sites and hydroxy groups on the pore walls can serve as a highly efficient heterogeneous catalyst to selectively reduce the imine bond in α,β-unsaturated imine substrates to afford unsaturated amine compounds.
- Niu, Zheng,Zhang, Weijie,Lan, Pui Ching,Aguila, Briana,Ma, Shengqian
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supporting information
p. 7420 - 7424
(2019/04/27)
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- Potassium Yttrium Ate Complexes: Synergistic Effect Enabled Reversible H2 Activation and Catalytic Hydrogenation
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A potassium yttrium benzyl ate complex was generated simply by mixing an yttrium amide and potassium benzyl. The benzyl ate complex could undergo peripheral deprotonation to produce a cyclometalated complex or hydrogenation to give a hydride ate complex. The latter hydride ate complex features a (KH)2 structure protected by two yttrium amide complexes. The synergistic effect between potassium hydride and the amide ligand enables the complex to deprotonate a methyl C-H bond. The combination of intramolecular deprotonation of the hydride ate complex and hydrogenation of the cyclometalated complex constitutes a reversible H2 activation process. Using this process involving formal addition and elimination of H2, we accomplished the catalytic hydrogenation of alkenes, alkynes, and imines.
- Zhai, Dan-Dan,Du, Hui-Zhen,Zhang, Xiang-Yu,Liu, Yu-Feng,Guan, Bing-Tao
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p. 8766 - 8771
(2019/09/30)
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- Direct Reductive Amination of Carbonyl Compounds Catalyzed by a Moisture Tolerant Tin(IV) Lewis Acid
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Despite the ever-broadening applications of main-group ‘frustrated Lewis pair’ (FLP) chemistry to both new and established reactions, their typical intolerance of water, especially at elevated temperatures (>100 °C), represents a key barrier to their mainstream adoption. Herein we report that FLPs based on the Lewis acid iPr3SnOTf are moisture tolerant in the presence of moderately strong nitrogenous bases, even under high temperature regimes, allowing them to operate as simple and effective catalysts for the reductive amination of organic carbonyls, including for challenging bulky amine and carbonyl substrate partners. (Figure presented.).
- Sapsford, Joshua S.,Scott, Daniel J.,Allcock, Nathan J.,Fuchter, Matthew J.,Tighe, Christopher J.,Ashley, Andrew E.
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supporting information
p. 1066 - 1071
(2018/01/27)
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- Metal-Free Carbonylation Route to a Reactive Borataepoxide System
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Hydroboration of N-allyl-cis-2,6-dimethylpiperidine with HB(C6F5)2 gave the trimethylene-bridged frustrated N/B Lewis pair 7. It featured a trans-2,6-dimethyl substitution pattern at the piperidine unit which indicated preceding equilibration with its iminium cation/hydridoborate isomer 6 by means of an internal hydride transfer. In situ generated compound 6 is essential for the reaction with CO/HB(C6F5)2 to give the borataepoxide product 12 at the [N]-(CH2)3-[B] framework. The borataepoxide 12 reacts rapidly with CO2, cleaves the acidic C-H bond of a terminal alkyne, splits dihydrogen, and reacts with nitriles and benzaldehyde. Most products were characterized by X-ray diffraction.
- Wang, Tongdao,Kehr, Gerald,Daniliuc, Constantin G.,Erker, Gerhard
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supporting information
p. 1040 - 1049
(2018/03/30)
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- LiAlH4: From Stoichiometric Reduction to Imine Hydrogenation Catalysis
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Imine-to-amine conversion with catalytic instead of stoichiometric quantities of LiAlH4 is demonstrated (85 °C, catalyst loading≥2.5 mol %, pressure≥1 bar). The effects of temperature, pressure, solvent, and catalyst modifications, as well as the substrate scope are discussed. Experimental investigations and preliminary DFT calculations suggest that the catalytically active species is generated in situ: LiAlH4+Ph(H)C=NtBu→LiAlH2[N(tBu)CH2Ph]2. A cooperative mechanism in which Li and Al both play a prominent role is proposed.
- Elsen, Holger,F?rber, Christian,Ballmann, Gerd,Harder, Sjoerd
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p. 7156 - 7160
(2018/05/30)
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- Alkali Metal Species in the Reversible Activation of H2
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MP(tBu)2 (M=Li, Na, K), KH and KN(SiMe3)2 are shown to activate HD reversibly. In the case of MP(tBu)2 this leads to isotopic scrambling and the formation of H2, D2, H(D)P(tBu)2 and MH(D) in C6D6. In toluene, KP(tBu)2 reacts with H2 but also leads to isotopic scrambling into the methyl groups of the solvent toluene. DFT calculations reveal that these systems effect H2 activation via cooperative interactions with the Lewis acidic alkali metal and the basic phosphorus, carbanion, or hydride centres, mimicking frustrated Lewis pair (FLP) behaviour.
- Xu, Maotong,Jupp, Andrew R.,Qu, Zheng-Wang,Stephan, Douglas W.
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supporting information
p. 11050 - 11054
(2018/07/30)
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- Conversion of aldimines to secondary amines using iron-catalysed hydrosilylation
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Iron-catalyzed hydrosilylation of imines to amines using a well-defined iron complex is reported. This method employs relatively mild conditions, by reaction of imine, (EtO)3SiH in a 1 : 2 ratio in the presence of 1 mol% precatalyst ([BIAN]Fe(η6-toluene), 3, BIAN = bis(2,6-diisopropylaniline)acenaphthene) at 70 °C. A broad scope of imines was readily converted into the corresponding secondary amines without the need for precatalyst activators.
- Saini, Anu,Smith, Cecilia R.,Wekesa, Francis S.,Helms, Amanda K.,Findlater, Michael
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supporting information
p. 9368 - 9372
(2019/01/03)
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- Selective formation of heterocyclic: Trans -cycloalkenes by alkyne addition to a biphenylene-based phosphane/borane frustrated Lewis pair
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The intramolecular 1-PMes2/8-B(C6F5)2 substituted biphenylene frustrated Lewis pair 4 shows some behavior reminiscent of intermolecular FLP systems. It undergoes trans-1,2-addition to a series of 1-alkynes to give the respective heterocyclic eight-membered E-alkenes 8. The P/B FLP 4 also reacts with triplet dioxygen to yield the [P]-O-[B](OC6F5) containing oxygenation product.
- Li, Jun,Daniliuc, Constantin G.,Kehr, Gerald,Erker, Gerhard
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supporting information
p. 6344 - 6347
(2018/06/22)
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- Direct Reductive N-Functionalization of Aliphatic Nitro Compounds
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The first general protocol for the direct reductive N-functionalization of aliphatic nitro compounds is presented. The nitro group is partially reduced to a nitrenoid, with a mild and readily available combination of B2pin2 and zinc organyls. Thereby, the formation of an unstable nitroso intermediate is avoided, which has so far severely limited reductive transformations of aliphatic nitro compounds. The reaction is concluded by an electrophilic amination of zinc organyls.
- Rauser, Marian,Ascheberg, Christoph,Niggemann, Meike
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p. 3970 - 3974
(2018/02/26)
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- Expanding the Boundaries of Water-Tolerant Frustrated Lewis Pair Hydrogenation: Enhanced Back Strain in the Lewis Acid Enables the Reductive Amination of Carbonyls
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The development of a boron/nitrogen-centered frustrated Lewis pair (FLP) with remarkably high water tolerance is presented. As systematic steric tuning of the boron-based Lewis acid (LA) component revealed, the enhanced back-strain makes water binding increasingly reversible in the presence of relatively strong base. This advance allows the limits of FLP's hydrogenation to be expanded, as demonstrated by the FLP reductive amination of carbonyls. This metal-free catalytic variant displays a notably broad chemoselectivity and generality.
- Dorkó, éva,Szabó, Márk,Kótai, Bianka,Pápai, Imre,Domján, Attila,Soós, Tibor
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supporting information
p. 9512 - 9516
(2017/08/01)
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- Expanding Water/Base Tolerant Frustrated Lewis Pair Chemistry to Alkylamines Enables Broad Scope Reductive Aminations
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Lower Lewis acidity boranes demonstrate greater tolerance to combinations of water/strong Br?nsted bases than B(C6F5)3, this enables Si?H bond activation by a frustrated Lewis pair (FLP) mechanism to proceed in the presence of H2O/alkylamines. Specifically, BPh3has improved water tolerance in the presence of alkylamines as the Br?nsted acidic adduct H2O–BPh3does not undergo irreversible deprotonation with aliphatic amines in contrast to H2O–B(C6F5)3. Therefore BPh3is a catalyst for the reductive amination of aldehydes and ketones with alkylamines using silanes as reductants. A range of amines inaccessible using B(C6F5)3as catalyst, were accessible by reductive amination catalysed by BPh3via an operationally simple methodology requiring no purification of BPh3or reagents/solvent. BPh3has a complementary reductive amination scope to B(C6F5)3with the former not an effective catalyst for the reductive amination of arylamines, while the latter is not an effective catalyst for the reductive amination of alkylamines. This disparity is due to the different pKavalues of the water–borane adducts and the greater susceptibility of BPh3species towards protodeboronation. An understanding of the deactivation processes occurring using B(C6F5)3and BPh3as reductive amination catalysts led to the identification of a third triarylborane, B(3,5-Cl2C6H3)3, that has a broader substrate scope being able to catalyse the reductive amination of both aryl and alkyl amines with carbonyls.
- Fasano, Valerio,Ingleson, Michael J.
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supporting information
p. 2217 - 2224
(2017/02/18)
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- Improved Buchner reaction selectivity in the copper-catalyzed reactions of ethyl 3-arylmethylamino-2-diazo-3-oxopropanoates
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Ethyl 3-alkyl(arylmethyl)amino-2-diazo-3-oxopropanoates (diazo amidoacetates) generate generally both cyclohepta[c]pyrrolones (Buchner products) and β-lactams (1,4-insertion products), and show obvious N-substituent-controlled chemoselectivity between the intramolecular Buchner reaction and aliphatic 1,4-C-H insertion under the catalysis of copper salts. The less steric N-alkyl substituents in the amide moiety generally favor the aliphatic 1,4-C-H insertion, while the more steric N-alkyl substituents generally favor the Buchner reaction. Compared with rhodium and ruthenium-catalyzed conditions, the current copper-catalyzed conditions improved the Buchner reaction selectivity of ethyl 3-alkyl(arylmethyl)amino-2-diazo-3-oxopropanoates.
- Liu, Jing,Tu, Jianzhuo,Yang, Zhanhui,Pak, Chol-Ung,Xu, Jiaxi
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p. 4616 - 4626
(2017/07/11)
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- REACTIONS OF STANNYL CATIONS
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The present invention relates to a method of reducing, cleaving and/or coupling at least one C=O, C-O, C=C or C=N bond of a compound, using a reagent comprising a stannyl cation.
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Page/Page column 22
(2018/01/17)
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- Efficient and Selective Hydrosilylation of Secondary and Tertiary Amides Catalyzed by an Iridium(III) Metallacycle: Development and Mechanistic Investigation
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Readily accessible cationic IrIII metallacycles catalyze efficiently the chemoselective hydrosilylation of tertiary and secondary amides to amines. The catalyst described herein operates at low loadings using inexpensive 1,1,3,3-tetramethyldisiloxane and allows fast reactions with high yields, selectivities, and turnover numbers. A transient iminium intermediate has been observed for the first time by using mass spectrometry, and the activation of the catalyst and the silane reagent have been studied by using DFT calculations. These fundamental insights support the present and future improvements of IrIII metallacycles through proper ligand modifications and enable further broad applications of catalysts based on metallacycles.
- Corre, Yann,Trivelli, Xavier,Capet, Frédéric,Djukic, Jean-Pierre,Agbossou-Niedercorn, Francine,Michon, Christophe
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p. 2009 - 2017
(2017/06/13)
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- Model beta - adrenergic receptor agonist universal hapten synthesis and application of (by machine translation)
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The present invention has offered a kind of beta - adrenergic receptor agonist universal hapten synthetic method and its application. The universal hapten with beta - adrenergic receptor agonists of common structure, can be used for preparing has the responsibility of broad spectrum beta - adrenergic receptor agonist antibody. The invention also relates to the general hapten in the synthesis intermediate for, and the general hapten preparation wide spectrum response of the marker antibody, including colloidal gold label, enzyme marker and fluorescent dye label. (by machine translation)
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Paragraph 0018
(2017/12/05)
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- Enhanced Catalytic Activity of Iridium(III) Complexes by Facile Modification of C,N-Bidentate Chelating Pyridylideneamide Ligands
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A set of aryl-substituted pyridylideneamide (PYA) ligands with variable donor properties owing to a pronounced zwitterionic and a neutral diene-type resonance structure were used as electronically flexible ligands at a pentamethylcyclopentadienyl (Cp) iridium center. The straightforward synthesis of this type of ligand allows for an easy incorporation of donor substituents such as methoxy groups in different positions of the phenyl ring of the C,N-bidentate chelating PYA. These modifications considerably enhance the catalytic activity of the coordinated iridium center toward the catalytic aerobic transfer hydrogenation of carbonyls and imines as well as the hydrosilylation of phenylacetylene. Moreover, these PYA iridium complexes catalyze the base-free transfer hydrogenation of aldehydes, and to a lesser extent also of ketones. Under standard transfer hydrogenation conditions including base, aldehydes are rapidly oxidized to carboxylic acids rather than reduced to the corresponding alcohol, as is observed under base-free conditions.
- Navarro, Miquel,Smith, Christene A.,Albrecht, Martin
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p. 11688 - 11701
(2017/10/10)
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- Switch in Catalyst State: Single Bifunctional Bi-state Catalyst for Two Different Reactions
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Disclosed here is a molecular switch which responds to acid-base stimuli and serves as a bi-state catalyst for two different reactions. The two states of the switch serve as a highly active and poorly active catalyst for two catalytic reactions (namely a hydrogenation and a dehydrogenative coupling) but in a complementary manner. The system was used in an assisted tandem catalysis set-up involving dehydrogenative coupling of an amine and then hydrogenation of the resulting imine product by switching between the respective states of the catalyst.
- Semwal, Shrivats,Choudhury, Joyanta
-
supporting information
p. 5556 - 5560
(2017/05/05)
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- Phosphine-Borane Frustrated Lewis Pairs Derived from a 1,1′-Disubstituted Ferrocene Scaffold: Synthesis and Hydrogenation Catalysis
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(Dimesitylphosphino)ferrocene (FcPMes2) (1) reacted with HB(C6F5)2 (2 equiv) by disproportionation to give adduct FcPMes2·H2B(C6F5) (4) plus B(C6F5)3, whereas 1-(dimesitylphosphino)-1′-vinylferrocene (2) was cleanly hydroborated with HB(C6F5)2 to afford [Fe(??5-C5H4PMes2)(??5-C5H4CH2CH2B(C6F5)2)] (7). Compound 7 adopted an open non-interacting P/B frustrated Lewis pair (FLP) structure in the crystal state as well as in a solution. This frustrated Lewis pair heterolytically cleaved dihydrogen under mild conditions to give the respective zwitterionic [P]H+/[B]H- phosphonium/hydroborate product, [Fe(??5-C5H4PHMes2){??5-C5H4CH2CH2BH(C6F5)2}] (8), which served as a catalyst for the hydrogenation of the electron-rich ?€-systems (imine, enamine) as well as the electron-deficient carbon-carbon double and triple bonds in some enones and an ynone under more forcing conditions (50 bar H2 pressure, 50 °C).
- Jian, Zhongbao,Krupski, Sergei,?koch, Karel,Kehr, Gerald,Daniliuc, Constantin G.,Císa?ová, Ivana,?těpni?ka, Petr,Erker, Gerhard
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p. 2940 - 2946
(2017/08/21)
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- A hydroboration route to geminal P/B frustrated Lewis pairs with a bulky secondary phosphane component and their reaction with carbon dioxide
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The secondary aryl-P(H) phosphanyl substituted tert-butylacetylenes 7a,b (aryl: Mes or Mes?) undergo hydroboration with [HB(C6F5)2] to give the geminal vinylidene-bridged P/B Lewis pairs 8a,b. The treatment of 8a,b with benzonitrile, N-sulfinylaniline, and phenyl isothiocyanate, respectively, gives the addition products 12a,b, 13a,b, and 14 with proton transfer from the phosphorus to the more basic nitrogen site. The reaction of the FLPs 8a,b with carbon dioxide yields a doubly boron bonded addition product. The reaction of 8b with a conjugated ynone formally proceeded by trans-1,2-hydrophosphination of the alkyne at the geminal FLP framework to give the seven-membered heterocycle 21.
- Jian, Zhongbao,Kehr, Gerald,Daniliuc, Constantin G.,Wibbeling, Birgit,Erker, Gerhard
-
supporting information
p. 11715 - 11721
(2017/09/18)
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- METHOD FOR HYDROGENATING UNSATURATED COMPOUND
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PROBLEM TO BE SOLVED: To provide a method for hydrogenating an unsaturated compound that uses crude gaseous hydrogen having carbon monoxide and carbon dioxide coexist with each other, as a hydrogen source. SOLUTION: A method for hydrogenating an unsaturated compound uses crude gaseous hydrogen as a hydrogen source and is performed in the presence of a frustrated Lewis pair. SELECTED DRAWING: None COPYRIGHT: (C)2018,JPOandINPIT
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-
Paragraph 0048
(2018/03/24)
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- REGULATORS FOR CONTROLLING LINEAR AND PSEUDO-RING EXPANSION POLYMERIZATION OF VINYL MONOMERS
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The invention concerns new regulator compounds for a novel polymerization process for vinyl monomers, which yields polymers with improved control over composition and nearly full to full conservation of architectural integrity up to high conversion. The regulator compounds are defined by according to anyone of the Formulas (1A), (1B), (1C), (1D), (1E), (1F), (1G), (1H) and (1I), wherein R1 stands for an optionally substituted secondary or tertiary alkyl or secondary or tertiary aralkyl; Z1 stands for -CN or a carboxylic acid ester of formula C(O)OR21; Z2 may be chosen from the group of -CN, carboxylic acid, salts of carboxylic acids, carboxylic acid ester, carboxylic acid amides, (hetero)aryl, alkenyl and halogen; R2, R3, R4 and R5 are each independently chosen from the group of H, alkyl, aralkyl, (hetero)aryl, -CN and carboxylic acid ester of formula C(O)OR22; R7 stands for a primary alkyl or primary aralkyl, -CN or hydrogen; Y stands for a bridging group and n is 2, 3, 4, 5 or 6; in case R1 stands for tertiary alkyl or tertiary aralkyl, R6 stands for a primary alkyl or primary aralkyl, -CN or a carboxylic acid ester of formula C(O)OR26; in case R1 stands for a secondary alkyl or secondary aralkyl, R6 stands for a primary or secondary alkyl or primary or secondary aralkyl, -CN, a carboxylic acid ester of formula C(O)OR26 or a phosphonic acid ester of formula P(O)(OR27)2, a (hetero)aryl or an alkenyl; R21, R22, R26 and R27 each independently stand for alkyl or aralkyi having from 1-30 carbon atoms, optionally containing heteroatoms.
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Page/Page column 31; 32
(2017/07/01)
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- Diazaphospholene Precatalysts for Imine and Conjugate Reductions
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The first examples of 1,3,2-diazaphospholene-catalyzed imine reduction and conjugate reduction reactions are reported. This approach employs readily synthesized alkoxydiazaphospholene precatalysts that can be handled in open air. Reduction of substrates containing Lewis basic functionality, isolated unsaturation, and protic functional groups was accomplished. The synthetic utility of this approach is demonstrated by the synthesis of the important antiparkinson medicine rasagiline and the natural product zingerone.
- Adams, Matt R.,Tien, Chieh-Hung,Huchenski, Blake S. N.,Ferguson, Michael J.,Speed, Alexander W. H.
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supporting information
p. 6268 - 6271
(2017/05/19)
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- Mild Metal-Free Hydrosilylation of Secondary Amides to Amines
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The combination of amide activation by Tf2O with B(C6F5)3-catalyzed hydrosilylation with TMDS constitutes a method for the one-pot reduction of secondary amides to amines under mild conditions. The method displays a broad applicability for the reduction of many types of substrates, and shows good compatibility and excellent chemoselectivity for many sensitive functional groups. Reductions of a multifunctionalized α,β-unsaturated amide obtained from another synthetic methodology, and a C-H functionalization product produced the corresponding amines in good to excellent yield. Chemoselective reduction of enantiomeric pure (ee >99%) tetrahydro-5-oxo-2-furaneamides yielded 5-(aminomethyl)dihydrofuran-2(3H)-ones in a racemization-free manner. The latter were converted in one pot to N-protected 5-hydroxypiperidin-2-ones, which are building blocks for the synthesis of many natural products. Further elaboration of an intermediate led to a concise four-step synthesis of -epi-pseudoconhydrine.
- Huang, Pei-Qiang,Lang, Qi-Wei,Wang, Yan-Rong
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p. 4235 - 4243
(2016/06/09)
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- Molecular Coordination-Switch in a New Role: Controlling Highly Selective Catalytic Hydrogenation with Switchability Function
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A molecular coordination-switch controlled by acid-base input has been developed and utilized in switchable catalysis. The molecular switch consists of a hybrid pyridylidene-benzimidazole ligand bound to an IrIIICp? moiety wherein the benzimidazole functionality has been utilized for acid/base controlled reversible coordination, switching between an IrIII-benzimidazole species (form I; neutral imino-type N-coordination) and an IrIII-benzimidazolate species (form II; anionic amido-type N-Ir bonding). Owing to the distinctly different nature of the metal-ligand bonding, it has been demonstrated that while the form I is almost inactive (TOF 1 h-1) in catalytic hydrogenation of imine under ambient pressure and temperature, the form II is greater than an order of magnitude more efficient (TOF 15.8 h-1) in the same catalysis. Moreover, the catalysis could be switched OFF and ON efficiently for several cycles with the addition of acid and base, respectively. Spectroscopic studies and kinetics have been performed to understand the switching activity.
- Semwal, Shrivats,Choudhury, Joyanta
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p. 2424 - 2428
(2016/04/26)
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- Zirconium-Catalyzed Imine Hydrogenation via a Frustrated Lewis Pair Mechanism
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Zirconium-based frustrated Lewis pairs (FLPs) are active imine hydrogenation catalysts under mild conditions. Complexes of the type [CpR2ZrOMes][B(C6F5)4] utilize the imine substrate itself as the Lewis base component of the FLP. Catalyst performance is a function of ligand structure; in general more bulky, more electron rich cyclopentadienyl derivatives give the best results. However, Cp? derivatives are not catalytically active, being stable after initial heterolytic cleavage of H2; this allows experimental verification of the competence of the zirconocene-imine pair in FLP-type heterolytic H2 cleavage. Enamines and protected nitriles are also hydrogenated if an additional internal phosphine base is used.
- Flynn, Stephanie R.,Metters, Owen J.,Manners, Ian,Wass, Duncan F.
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p. 847 - 850
(2016/04/19)
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- Structure-Reactivity Relationship in the Frustrated Lewis Pair (FLP)-Catalyzed Hydrogenation of Imines
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The autoinduced, frustrated Lewis pair (FLP)-catalyzed hydrogenation of 16-benzene-ring substituted N-benzylidene-tert-butylamines with B(2,6-F2C6H3)3 and molecular hydrogen was investigated by kinetic analysis. The pKa values for imines and for the corresponding amines were determined by quantum-mechanical methods and provided a direct proportional relationship. The correlation of the two rate constants k1 (simple catalytic cycle) and k2 (autoinduced catalytic cycle) with pKa difference between imine and amine pairs (ΔpKa) or Hammett's σ parameter served as useful parameters to establish a structure-reactivity relationship for the FLP-catalyzed hydrogenation of imines.
- Tussing, Sebastian,Kaupmees, Karl,Paradies, Jan
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supporting information
p. 7422 - 7426
(2016/05/24)
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- Intramolecular Lewis pairs with two acid sites-reactivity differences between P- and N-based systems
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The doubly acid-functionalised aniline PhN[(CH2)3B(C6F5)2]2 shows rapidly exchanging boron acid groups at the central base function and is an active frustrated Lewis pair due to cooperative hydride binding by both Lewis acids. Here we report investigations on the effect of different substituents at the central nitrogen atom and on the effect of exchanging nitrogen by phosphorus. Treatment of diallyl-tert-butylaniline with one equivalent of HB(C6F5)2 led to formation of a seven-membered iminium hydridoborate ring; after mono-hydroboration the intermediately formed frustrated Lewis pair reacts with the second allylamine function under ring closure. Phosphorus based Lewis pairs with two acid sites were prepared by hydroboration of diallylphenylphosphane and diallyl-tert-butylphosphane. Unlike the aniline PhN[(CH2)3B(C6F5)2]2 the doubly hydroborated species (tBu/Ph)P[(CH2)3B(C6F5)2]2 show no dynamic exchange of the boron Lewis acid functions in solution and are not catalytically active in terms of H/D-scrambling as well as hydrogenation reactions. Quantum-chemical investigations revealed the B-P bond dissociation Gibbs free energy to be much larger than those of the nitrogen analogue. The absence of an active open form in solution prevents an activity in heterolytic hydrogen splitting.
- K?rte, Leif A.,Blomeyer, Sebastian,Heidemeyer, Shari,Nissen, Jan Hendrick,Mix, Andreas,Neumann, Beate,Stammler, Hans-Georg,Mitzel, Norbert W.
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supporting information
p. 17319 - 17328
(2016/11/13)
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