- Synthesis of Oxazoles by Tandem Cycloisomerization/Allylic Alkylation of Propargyl Amides with Allylic Alcohols: Zn(OTf)2 as π Acid and σ Acid Catalyst
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A Zn(OTf)2-catalyzed tandem cycloisomerization/allylic alkylation of N-(propargyl)arylamides and allylic alcohols to produce oxazole derivatives has been successfully developed. The zinc catalyst served as π acid and also σ acid in this reaction. The target allylic oxazoles have been transformed into multisubstituted diene structures, which are potential aggregation-induced emission active optical materials.
- Wang, Bin,Chen, Ying,Zhou, Ling,Wang, Jianwu,Tung, Chen-Ho,Xu, Zhenghu
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- Experimental and theoretical investigation of the cycloisomerization of N-propargylcarboxamide catalyzed by NHC-Au-X in green solvents
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For the first time, NHC-Au-X [NHC = (1,3-bis(2,6-di-isopropylphenyl)-imidazol-2-ylidene, X? = BF4?, OTf?, OTs?, TFA?] catalysts were tested in the cycloisomerization of N-(prop-2-yn-yl)benzamide to 2-phenyl-5-vinylidene-2-oxazoline in a wide set of green solvents. We found that most of these solvents (cyclohexanone, isopropyl acetate, MIBK, ethyl lactate, furfuryl alcohol, γ-valerolactone, propylene carbonate and propionic acid) are comparable or better solvents with respect to traditional VOS. Furthermore, the catalyst activity is related to the basic strength of the anion and the performances of the catalysts decrease gradually with increasing basicity and hydrogen-bond acceptor power of X?. Kinetic experiments and DFT calculations seem to indicate that both the characteristic of the solvent and counterion should be taken into account.
- Segato, Jacopo,Baratta, Walter,Belanzoni, Paola,Belpassi, Leonardo,Del Zotto, Alessandro,Zuccaccia, Daniele
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- The core of the matter-arene substitution determines the coordination and catalytic behaviour of tris(1-phosphanyl-1′-ferrocenylene)arene gold(i) complexes
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Changing the aromatic core of C3-symmetric tris(ferrocenyl)arene-based tris-phosphanes has profound effects on their coordination behaviour towards gold(i). Depending on the arene (s-triazine, benzene, or trifluorobenzene), four different coordination modes can be distinguished and their preference has been rationalised using computational methods. The corresponding 1 : 1 ligand-to-metal complexes, studied by variable-temperature NMR spectroscopy, revealed fluctional behaviour in solution. Given the presence of up to three or six ferrocenylene spacers per complex, their electrochemistry was investigated. The redox-responsive nature of the complexes can be advantageously exploited in the catalytic ring-closing isomerisation of N-(2-propyn-1-yl)benzamide, where the benzene-based 2 : 3 ligand-to-metal complex has been shown to display multiple activity states depending on the degree of (reversible) oxidation in a preliminary trial.
- Coburger, Peter,Hey-Hawkins, Evamarie,Michak, Marvin,Ringenberg, Mark R.,Straube, Axel
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- Activation of a Metal-Halogen Bond by Halogen Bonding
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In recent years, the non-covalent interaction of halogen bonding (XB) has found increasing application in organocatalysis. However, reports of the activation of metal-ligand bonds by XB have so far been limited to a few reactions with elemental iodine or
- Erochok, Nikita,Guérin, Vincent,Heinen, Flemming,Huber, Florian,Huber, Stefan M.,Kirsch, Stefan F.,Legault, Claude Y.,Wolf, Julian
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- Gold-Catalyzed One-Pot Synthesis of Polyfluoroalkylated Oxazoles from N-Propargylamides Under Visible-Light Irradiation
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A gold-catalyzed synthesis of polyfluoroalkylated oxazoles from N-propargylamides under visible-light irradiation has been developed. These reactions display excellent compatibility of radicals and gold catalysts under visible-light irradiation. Mechanistic experiments indicate that polyfluoroalkyl iodides play a dual role in enhanced compatibility of radicals and gold catalysts through assisted protodeauration of vinyl gold and reactivated the gold catalyst. In addition, PPh3AuNTf2 not only activates N-propargylamide to generate vinyl gold intermediate, but also greatly promotes homolysis of polyfluoroalkyl iodides under blue light irradiation.
- Li, Pan,Liu, Yantao,Shi, Yating,Wei, Lanen,Xu, Xuejun,Zhang, Puyu,Zhao, Jingjing,Zhao, Ke
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- N-Cyclopropenio-imidazol-2-ylidene: An N-heterocyclic carbene bearing an N-cationic substituent
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A cationic NHC 1+ bearing an N-bound 2,3-bis(diisopropylamino)cyclopropenium group is reported. From an easily available dicationic imidazolium precursor, the coordination abilities and stereo-electronic properties of 1+ are evaluated by the formation of Pd(ii), Rh(i) and Au(i) complexes. The cationic gold(i) complex is implemented in representative intramolecular Au(i)-catalyzed cyclizations.
- Barthes, Cécile,César, Vincent,Canac, Yves,Duhayon, Carine
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- T-Shaped Gold→Stiborane Complexes as Carbophilic Catalysts: Influence of the Peripheral Substituents
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As part of our efforts toward the discovery of new late transition metal catalysts, we synthesized [(o-(Ph2P)C6H4)2(o-C6Cl4O2)SbPh)Au]+ (3+) and [(o-(iPrsu
- Sen, Srobona,Ke, Iou-Sheng,Gabba?, Fran?ois P.
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- Heteromultimetallic Complexes with Redox-Active Mesoionic Carbenes: Control of Donor Properties and Redox-Induced Catalysis
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Mesoionic carbenes (MICs) are currently hugely popular as ligands, and triazolylidenes are arguably the most prominent classes of such MICs. Mesoionic carbenes with ferrocenyl substituents are presented that can act as metalloligands for the generation of heteromultimetallic iridium(I) and gold(I) complexes. The ferrocenyl substituents allow for reversible oxidation of these heteromultimetallic complexes, and these oxidation steps have a strong influence on the donor properties of the MICs. Tolman electronic parameters (TEP) determined from analysis of the iridium–carbonyl complexes show that the neutral ferrocenyl–MIC ligands are stronger donors than the imidazolylidene based carbenes, the one-electron oxidized ferrocenyl MICs are in the range of the tricyclohexyl phosphines and the two-electron oxidized forms, which are electron-poor, lie in the range of triphenyl phosphines. Taking advantage of the generation of these electron-poor MICs, we show their gold(I) complexes are potent catalysts for the synthesis of oxazolines, with complexes of the oxidized MIC ligands, without any additional additive, outperforming their neutral counterparts by almost a factor of ten. These results thus present the first examples of MIC ligands that are reversibly electronically tunable, and show the potential of the oxidized MIC ligands in types of catalysis where electron-poor ligands are necessary. The potential of MICs for molecular electroactive materials is also shown.
- Hettmanczyk, Lara,Suntrup, Lisa,Klenk, Sinja,Hoyer, Carolin,Sarkar, Biprajit
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- Novel zwitterionic complexes arising from the coordination of an ambiphilic phosphorus-aluminum ligand to gold
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Coordination of Mes2PC(CHPh)AltBu2 to metal chlorides has been studied. Bridging P→M-Cl→Al coordinations were observed with Rh and Pd fragments, while chloride abstraction systematically occurred with gold. The resulting zwitterionic
- Devillard, Marc,Nicolas, Emmanuel,Appelt, Christian,Backs, Jana,Mallet-Ladeira, Sonia,Bouhadir, Ghenwa,Slootweg, J. Chris,Uhl, Werner,Bourissou, Didier
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- Phosphinines versus mesoionic carbenes: a comparison of structurally related ligands in Au(i)-catalysis
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Gold(i) complexes based on a 2,4,6-triarylphosphinine and a mesoionic carbene derivative have been prepared and characterized crystallographically. Although structurally related, both heterocycles differ significantly in their donor/acceptor properties. These opposed electronic characteristics have been exploited in Au(i)-catalyzed cycloisomerization reactions. For the conversion of the standard substrate dimethyl 2-(3-methylbut-2-enyl)-2-(prop-2-ynyl)malonate the results obtained for both Au-catalysts were found to be very similar and comparable to the ones reported in the literature for other carbene- or phosphorus(iii)-based Au(i)-complexes. In contrast, a clear difference between the catalytic systems was found for the cycloisomerization of the more challenging substrate N-2-propyn-1-ylbenzamide. A combination of the phosphinine-based complex and [AgSbF6] or [Cu(OTf)2] leads to a catalytic species, which is more active than the mesoionic carbene-based coordination compound. We attribute these differences to the stronger π-accepting ability of phosphinines in comparison to mesoionic carbenes. The here presented results show for the first time that phosphinines can be used efficiently as π-accepting ligands in Au(i)-catalyzed cycloisomerization reactions.
- Rigo, Massimo,Hettmanczyk, Lara,Heutz, Frank J. L.,Hohloch, Stephan,Lutz, Martin,Sarkar, Biprajit,Müller, Christian
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- Catalytic ring-closing reactions of gold compounds containing bis(phosphino)ferrocene ligands
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The efficiency of various gold compounds containing bis(phosphino)ferrocene ligands for catalyzing ring-closing reactions was examined. Six commercially available bis(phosphino)ferrocene ligands: 1,1′-bis(ditert-butylphosphino)ferrocene (dtbpf), 1,1′-bis(
- Michaels, Toni A.,Pritchard, Olivia F.,Dell, Justine S.,Bezpalko, Mark W.,Kassel, W. Scott,Nataro, Chip
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- Heterobimetallic complexes with redox-active mesoionic carbenes as metalloligands: electrochemical properties, electronic structures and catalysis
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A mesoionic carbene with a ferrocene backbone is used as a metalloligand to generate the first example of their Fe-Au heterobimetallic complexes. The details of geometric and electronic structures in different redox states and preliminary catalytic result
- Hettmanczyk, Lara,Manck, Sinja,Hoyer, Carolin,Hohloch, Stephan,Sarkar, Biprajit
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- Synthesis and Properties of Hydrazino Amino Acyclic Carbenes of Gold(I), Platinum(II), Palladium(II) and Rhodium(III)
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The nucleophilic addition of protected and substituted hydrazine derivatives to isonitrile complexes of gold(I), platinum(II), palladium(II) and rhodium(III) provides the corresponding hydrazino amino acyclic carbene complexes. These are characterized by
- T?upova, Svetlana,Rudolph, Matthias,Rominger, Frank,Hashmi, A. Stephen K.
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- Highly Electrophilic, Catalytically Active and Redox-Responsive Cobaltoceniumyl and Ferrocenyl Triazolylidene Coinage Metal Complexes
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A convenient access to a triad of triazoles with ferrocenyl and cobaltoceniumyl substituents is reported. N-Alkylation, deprotonation and metalation with CuI/AgI/AuI synthons affords the heteroleptic triazolylidene complexes. Due to the combination of neutral, electron-donating ferrocenyl substituents and cationic, strongly electron-withdrawing cobaltocenium substituents, the mesoionic carbene (MIC) ligands of these complexes are electronically interesting “push–pull”, “pull–push” and “pull–pull” metalloligands with further switchable redox states based on their fully reversible FeII/FeIII, (ferrocene/ferrocenium) and CoIII/CoII, (cobaltocenium/cobaltocene) redox couples. These are the first examples of metal complexes of (di)cationic NHC ligands based on cobaltoceniumyl substituents. DFT calculated Tolman electronic parameter (TEP) of the new MIC ligands, show these metalloligands to be extremely electron-poor NHCs with properties unmatched in other carbene chemistry. Utilization of these multimetallic electronically tunable compounds in catalytic oxazoline synthesis and in antitumor studies are presented. Remarkably, 1 mol % of the AuI complex with the dicationic MIC ligand displays full catalytic conversion, without the need for any other additives, in less than 2 hours at ambient temperatures. These results thus firmly establish these new classes of cobaltoceniumyl based (di)cationic MIC ligands as prominent players in several branches of chemistry.
- Vanicek, Stefan,Podewitz, Maren,Stubbe, Jessica,Schulze, Dennis,Kopacka, Holger,Wurst, Klaus,Müller, Thomas,Lippmann, Petra,Haslinger, Simone,Schottenberger, Herwig,Liedl, Klaus R.,Ott, Ingo,Sarkar, Biprajit,Bildstein, Benno
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- Metal Confinement through N-(9-Alkyl)fluorenyl-Substituted N-Heterocyclic Carbenes and Its Consequences in Gold-Catalysed Reactions Involving Enynes
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A series of gold(I) and gold(III) complexes containing bulky bis-N,N′-(9-alkylfluorenyl) heterocyclic carbene (RF-NHC) ligands have been prepared in high yields from appropriate imidazolinium, imidazolium and benzimidazolium salts. In all complexes, the carbene ligand provides high steric protection of the Au?X bond trans to the carbenic C atom. Irrespective of the metal oxidation state, the complexes showed high efficiency in a tandem 3,3-rearrangement/Nazarov reaction of an enynyl acetate. One of the AuIII complexes, [AuCl3(RF-NHC)], was further found to be suitable for the efficient cyclisation of a propargylcarboxamide. Furthermore, unlike related NHC–gold(I) complexes based on conventional bulky N-heterocyclic carbenes (notably, 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr), 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) and 1,3-(bis-tert-butyl)imidazol-2-ylidene (ItBu)), the studied [AuICl(RF-NHC)] complexes catalysed the conversion of a 1,6-enyne in the presence of indole into a single product; this arises from the embracing character of the ligand, which prevents indole addition on one of the catalytic intermediates. A structure/selectivity relationship was established for all carbenes tested that took into account percent buried volumes and topographic steric maps. The results illustrate the high potential of confining NHCs in organic synthesis.
- Teci, Matthieu,Hueber, Damien,Pale, Patrick,Toupet, Lo?c,Blanc, Aurélien,Brenner, Eric,Matt, Dominique
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- Access to a Cationic, Electron-Poor N-Heterocyclic Carbene with a Quinazolinium Core by Postsynthetic Modification of Related Neutral Derivatives
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Derivatives of cationic six-membered N-heterocyclic carbene G with a quinazolinium scaffold are easily obtained by abstraction of an alcoholate group from related neutral precursors which are easily accessible. On the basis of this route, chalcogene adducts and metal complexes of G, which is a benzo-anellated pyrimidiniumylidene, could be prepared. Evaluation of the ligand properties by IR and 77Se NMR spectroscopy indicate that cationic carbene G is a much more powerful π-acceptor (δ(77Se): 768 ppm) and a significantly weaker overall donor (TEP: 2073 cm-1) than related neutral carbene 4 (361 ppm, 2054 cm-1). DFT calculations provide a rationale for these experimental observations. AuCl complexes of both carbenes were used as catalysts for the cyclization of a propargylamide to a methyleneoxazoline. The complex containing the cationic carbene featured a much higher activity.
- Brüggemann, Peter,Wahl, Michaela,Schwengers, Sebastian,Buhl, Hannes,Ganter, Christian
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- Triple the fun: Tris(ferrocenyl)arene-based gold(i) complexes for redox-switchable catalysis
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The modular syntheses of C3-symmetric tris(ferrocenyl)arene-based tris-phosphanes and their homotrinuclear gold(i) complexes are reported. Choosing the arene core allows fine-tuning of the exact oxidation potentials and thus tailoring of the electrochemical response. The tris[chloridogold(i)] complexes were investigated in the catalytic ring-closing isomerisation of N-(2-propyn-1-yl)benzamide, showing cooperative behaviour vs. a mononuclear chloridogold(i) complex. Adding one, two, or three equivalents of 1,1'-diacetylferrocenium[tetrakis(perfluoro-tert-butoxy)aluminate] as an oxidant during the catalytic reaction (in situ) resulted in a distinct, stepwise influence on the resulting catalytic rates. Isolation of the oxidised species is possible, and using them as (pre-)catalysts (ex situ oxidation) confirmed the activity trend. Proving the intactness of the P-Au-Cl motif during oxidation, the tri-oxidised benzene-based complex has been structurally characterised. This journal is
- Coburger, Peter,Dütsch, Luis,Hey-Hawkins, Evamarie,Straube, Axel
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- Gold(ii) in redox-switchable gold(i) catalysis
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Gold(ii) species catalyse the cyclisation of N(2-propyn-1-yl)benzamide to 2-phenyl-5-vinylidene-2-oxazoline without halide abstraction while the saturated gold(i) complex is inactive. Redox-switching between gold(ii) and gold(i) turns catalytic turnover o
- Veit, Philipp,Volkert, Carla,F?rster, Christoph,Ksenofontov, Vadim,Schlicher, Steffen,Bauer, Matthias,Heinze, Katja
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- Bicyclic (amino)(borata)carbene derived from diazadiborinine and isonitrile
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The reaction of 1,4,2,5-diazadiborinine (1) with two equivalents of an aryl isonitrile afforded a bicyclic product containing an indole unit (2) or ketenimine moiety (3), suggesting the generation of a B,N-carbene intermediate formed via a [4+2] cycloaddi
- Wang, Baolin,Koshino, Kota,Kinjo, Rei
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- Sterically Demanding AgI and CuI N-Heterocyclic Carbene Complexes: Synthesis, Structures, Steric Parameters, and Catalytic Activity
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The synthesis and full characterization of new air-stable AgI and CuI complexes bearing structurally bulky expanded-ring N-heterocyclic carbene (erNHC) ligands is presented. The condensation of protonated NHC salts with Ag2/sub
- Cervantes-Reyes, Alejandro,Rominger, Frank,Hashmi, A. Stephen K.
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- The Power of Ferrocene, Mesoionic Carbenes, and Gold: Redox-Switchable Catalysis
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Catalysis with gold(I) complexes is a useful route for synthesizing a variety of important heterocycles. Often, silver(I) additives are necessary to increase the Lewis acidity at the gold(I) center and to make them catalytically active. We present here a
- Klenk, Sinja,Rupf, Susanne,Suntrup, Lisa,Van Der Meer, Margarethe,Sarkar, Biprajit
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- Gold catalysis: Isolation of vinylgold complexes derived from alkynes
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Gold plated rings: N-Propargylcarboxamides (1) when reacted with a gold complex containing the IPr N-heterocyclic carbene ligand, delivers the first isolable vinylgold intermediates obtained from alkynes. [see Scheme; IPr = 1, 3-bis(2,6diisopropylphenyl)i
- Hashmi, A. Stephen K.,Schuster, Andreas M.,Rominger, Frank
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- N-Heterocyclic Iod(az)olium Salts – Potent Halogen-Bond Donors in Organocatalysis
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This article describes the application of N-heterocyclic iod(az)olium salts (NHISs) as highly reactive organocatalysts. A variety of mono- and dicationic NHISs are described and utilized as potent XB-donors in halogen-bond catalysis. They were benchmarked in seven diverse test reactions in which the activation of carbon- and metal-chloride bonds as well as carbonyl and nitro groups was achieved. N-methylated dicationic NHISs rendered the highest reactivity in all investigated catalytic applications with reactivities even higher than all previously described monodentate XB-donors based on iodine(I) and (III) and the strong Lewis acid BF3.
- Boelke, Andreas,Kuczmera, Thomas J.,Lork, Enno,Nachtsheim, Boris J.
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p. 13128 - 13134
(2021/08/09)
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- Silver-Free Au(I) Catalysis Enabled by Bifunctional Urea- and Squaramide-Phosphine Ligands via H-Bonding
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A library of gold(I) chloride complexes with phosphine ligands incorporating pendant (thio)urea and squaramide H-bond donors was prepared with the aim of promoting chloride abstraction from Au(I) via H-bonding. In the absence of silver additives, complexes bearing squaramides and trifluoromethylated aromatic ureas displayed good catalytic activity in the cyclization of N-propargyl benzamides, as well as in a 1,6-enyne cycloisomerization, a tandem cyclization-indole addition reaction and the hydrohydrazination of phenylacetylene. Kinetic studies and DFT calculations indicate that the energetic span of the reaction is accounted by both the chloride abstraction step, facilitated by the bidentate H-bond donor via an associative mechanism, and the subsequent cyclization step.
- Echavarren, Antonio M.,Franchino, Allegra,Martí, àlex,Nejrotti, Stefano
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p. 11989 - 11996
(2021/07/06)
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- Synthesis and Catalytic Applications of Multinuclear Gold(I)-1,2,3-Triazolylidene Complexes
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A series of mono- to trinuclear gold(I) complexes (1–3) supported by oxo-functionalized 1,2,3-triazolylidenes have been prepared. All new compounds were fully characterized by means of 1H and 13C NMR spectroscopy, elemental analyses, and in the case of complexes 1 and 2 by x-ray diffraction. The catalytic performance of the new triazolylidene gold complexes was tested in several hydroelementation and cyclization processes employing a variety of alkynes as starting materials. According to the overall results, the trinuclear complex 3 displayed the highest catalytic activity in all processes, providing good to excellent yields under mild reaction conditions.
- Rendón-Nava, David,álvarez-Hernández, Alejandro,Mendoza-Espinosa, Daniel
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supporting information
p. 840 - 847
(2021/02/26)
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- Asymmetric Allylation by Chiral Organocatalyst-Promoted Formal Hetero-Ene Reactions of Alkylgold Intermediates
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An unprecedented catalytic asymmetric allylation of isatins and isatin-derived ketimines is reported enabled by a gold and chiral organocatalyst cooperative catalysis strategy. This method offers expeditious access to chiral 2,5-disubsituted alkylideneoxazolines containing vicinal stereogenic centers, mainly in optically pure form, and which are otherwise impossible to access. Mechanistic evidence reveals the presence of an alkylgold intermediate, and an X-ray crystal structure of the allylgold species illuminates its unique stability and reactivity. An asymmetric formal hetero-ene reaction of this gold intermediate, involving a dearomatization process, is enabled with assistance of a quinine-derived squaramide catalyst. This novel discovery extends the synthetic applications of gold complexes and the versatility of gold catalysis.
- Dong, Guizhi,Bao, Ming,Xie, Xiongda,Jia, Shikun,Hu, Wenhao,Xu, Xinfang
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supporting information
p. 1992 - 1999
(2020/11/30)
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- Water Can Accelerate Homogeneous Gold Catalysis
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A selection of gold-catalyzed reactions was examined in a kinetic study on the influence of water on the rate constant. Two intramolecular reactions and one intermolecular reaction, which proceed via proton transfer and/or protodeauration steps, were inve
- Hashmi, A. Stephen K.,Rudolph, Matthias,Stein, Philipp M.
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supporting information
p. 4264 - 4271
(2021/08/03)
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- Merging Gold/Copper Catalysis and Copper/Photoredox Catalysis: An Approach to Alkyl Oxazoles from N-Propargylamides
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Here, we report a mild and highly efficient approach to alkyl oxazoles through merging gold/copper catalysis and copper/photoredox catalysis. Various alkyl oxazoles are synthesized from N-propargylamides with alkyl halides in good to excellent yields with
- Liu, Yantao,Zhu, Keyong,Kong, Yuting,Li, Xiao,Cui, Jie,Xia, Yifan,Zhao, Jingjing,Duan, Shaofeng,Li, Pan
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p. 18247 - 18256
(2021/12/17)
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- Alkyne Trifunctionalization via Divergent Gold Catalysis: Combining π-Acid Activation, Vinyl-Gold Addition, and Redox Catalysis
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Here we report the first example of alkyne trifunctionalization through simultaneous construction of C-C, C-O, and C-N bonds via gold catalysis. With the assistance of a γ-keto directing group, sequential gold-catalyzed alkyne hydration, vinyl-gold nucleophilic addition, and gold(III) reductive elimination were achieved in one pot. Diazonium salts were identified as both electrophiles (N source) and oxidants (C source). Vinyl-gold(III) intermediates were revealed as effective nucleophiles toward diazonium, facilitating nucleophilic addition and reductive elimination with high efficiency. The rather comprehensive reaction sequence was achieved with excellent yields (up to 95%) and broad scope (>50 examples) under mild conditions (room temperature or 40 °C).
- Yuan, Teng,Tang, Qi,Shan, Chuan,Ye, Xiaohan,Wang, Jin,Zhao, Pengyi,Wojtas, Lukasz,Hadler, Nicholas,Chen, Hao,Shi, Xiaodong
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supporting information
p. 4074 - 4082
(2021/04/06)
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- Silica-Supported Phosphine–Gold Complexes as an Efficient Catalytic System for a Dearomative Spirocyclization
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The combination of metal catalyst and inorganic silica frameworks provides a greener approach to recyclable catalysis. In this study, three phosphine–gold chloride complexes have been successfully covalently grafted onto chiral silica nanohelices. The resulting 3D ensembles showed chiroptical properties that allowed the monitoring of the supported ligands. The heterogeneous gold chloride catalysts in cooperation with silver triflate exhibited high reactivity in various reactions, especially in the spirocyclization of aryl alkynoate esters, for which a catalytic loading of 0.05 mol % could be employed. The heterogeneous catalysts could be easily recovered and recycled seven or eight times without any loss of efficiency. By adding more silver triflate, 25 cycles with full conversion were achieved owing to a complex catalytic system based on silica and metallic species.
- Bibal, Brigitte,Buffière, Sonia,Cao, Zhen,Nlate, Sylvain,Oda, Reiko,Pouget, Emilie,Scalabre, Antoine
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p. 427 - 433
(2020/12/03)
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- InCl3-catalyzed 5- exo-dig cyclization/1,6-conjugate addition of N -propargylamides with p -QMs to construct oxazole derivatives
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An InCl3-catalyzed atom-economic intramolecular 5-exo-dig cyclization/1,6-conjugate addition/aromatization of N-propargylamides with p-QMs to produce oxazoles tethering diarylmethane has been successfully developed. InCl3 not only se
- Li, Ming,Li, Xue,Nan, Guang-Ming,Wen, Li-Rong,Yan, Ting-Xun,Yao, Tian-Yu
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p. 1780 - 1784
(2020/03/17)
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- Dual H-bond activation of NHC-Au(i)-Cl complexes with amide functionalized side-arms assisted by H-bond donor substrates or acid additives
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Novel approach with amide-tethered H-bond donor NHC ligands enabled Au(i)-catalysis via H-bonding. The plain NHC-Au(i)-Cl complex catalysed conversions of terminal N-propynamides to oxazolines, and enyne cycloisomerization with an acid additive, in DCM at
- Sepp?nen, Otto,Aikonen, Santeri,Muuronen, Mikko,Alamillo-Ferrer, Carla,Burés, Jordi,Helaja, Juho
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p. 14697 - 14700
(2020/12/02)
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- Regioselective Crossed Aldol Reactions under Mild Conditions via Synergistic Gold-Iron Catalysis
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A synergistic gold-iron (Au-Fe) catalytic system was developed for sequential alkyne hydration and vinyl Au addition to aldehydes or ketones. Fe(acac)3 was identified as an essential co-catalyst in preventing vinyl Au protodeauration and facilitating nucleophilic additions. Effective C–C bond formation was achieved under mild conditions (room temperature) with excellent regioselectivity and high efficiency (1% [Au], up to 95% yields). The intramolecular reaction was also achieved, giving successful macrocyclization (16–31 ring sizes) with excellent yields (up to 90%, gram scale) without extended dilution (0.2 M), which highlights the great potential of this new crossed aldol strategy in challenging target molecule synthesis. Effective construction of the C–C bond is one of the most important tasks in organic synthesis. Whereas aldol condensation is a classic C–C bond-forming transformation, it requires other chemical promoters, such as strong base and reactive acidic catalysts. As a result, the overall transformation is limited in terms of ideal atom economy and environmentally friendly operation. With the discovery of a gold-iron (Au-Fe) synergistic catalysis system, here we describe a new approach to facilitating alkyne hydration and sequential vinyl Au addition to carbonyls. This approach gives the C–C bond-forming products in excellent yields, wide substrate scope, and great functional-group compatibility under mild conditions. This protocol can also be applied to macrocyclization without extended dilution. This C–C bond-forming strategy could facilitate challenging molecule synthesis in chemical, biological, and medicinal research. We report a synergistic gold-iron (Au-Fe) catalytic system to access vinyl Au reactivity by avoiding frequently occurring protodeauration. Fe(acac)3 was identified as an essential co-catalyst, facilitating vinyl Au addition to aldehydes. A broad substrate scope was obtained under mild conditions (room temperature) with excellent regioselectivity and high efficiency (1% [Au], up to 95% yields). This protocol offers a practical solution for achieving macrocyclization (16–31 ring sizes, up to 90%, gram scale) without extended dilution, highlighting the synthetic utility in complex molecular synthesis.
- Chen, Hao,Jean, Jonathan,Shan, Chuan,Shi, Xiaodong,Teng, Shun,Wang, Jin,Wojtas, Lukasz,Ye, Xiaohan,Yi, Yaping,Yuan, Teng,Zhao, Pengyi
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supporting information
p. 1420 - 1431
(2020/06/19)
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- Assessing the influence of phosphine substituents on the catalytic properties of self-stabilised digold(i) complexes with supporting ferrocene phosphinonitrile ligands
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Gold(i) phosphine complexes are often used in catalysis, but the role of their auxiliary ligands still remains poorly understood. Thus, building on our previous research, we prepared a series of Au(i) complexes [Au2(μ-R2PfcCN)2][SbF6]2 (fc = ferrocene-1,1
- Barta, Ondrej,Cisarova, Ivana,Schulz, Jiri,Stepnicka, Petr
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p. 11258 - 11262
(2019/07/31)
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- Fluorocyclization of N-Propargylamides to Oxazoles by Electrochemically Generated ArIF2
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A sustainable synthesis of 5-fluoromethyl-2-oxazoles by use of electrochemistry has been demonstrated. Hypervalent ArIF2 is generated by direct electrochemical oxidation of iodoarene ArI in Et3N·5HF and mediates the fluorocyclization
- Berger, Michael,Herszman, John D.,Waldvogel, Siegfried R.
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- Photoreduction of Thioether Gold(III) Complexes: Mechanistic Insight and Homogeneous Catalysis
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Complexes formed between AuCl3 and thioether ligands underwent a photoinduced reductive elimination under homogeneous conditions in dichloromethane and toluene solutions to afford the corresponding AuI complexes. All the gold(III) complexes were rapidly reduced to the gold(I) chloride complexes under 365 nm irradiation or ambient light while being thermally stable below 55 °C. The mechanism of photoreduction through Cl2 elimination is discussed based on a kinetic study and the chemical trapping of chlorine species: Cl2, radical Cl., and possibly Cl+. The catalytic activities of the gold(III) chloride complexes and the corresponding gold(I) complexes obtained by in situ reduction were evaluated in the cyclization of N-propargylic amides to oxazoles. The merits of such photoreducible complexes in homogeneous gold catalysis are illustrated by a cascade reaction catalyzed by thioether gold complexes that affords a 4H-quinolizin-4-one in high yields.
- Cao, Zhen,Bassani, Dario M.,Bibal, Brigitte
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supporting information
p. 18779 - 18787
(2018/11/23)
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- Sequential Au/Cu Catalysis: A Two Catalyst One-Pot Protocol for the Enantioselective Synthesis of Oxazole α-Hydroxy Esters via Intramolecular Cyclization/Intermolecular Alder-Ene Reaction
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A convenient protocol for the enantioselective synthesis of oxazole α-hydroxy ester derivatives 4 from readily available propargylamides 1 and alkylglyoxylates 3 was developed. The first step of the one-pot procedure is the selective intramolecular in situ formation of an alkylideneoxazoline 2, which then in an intermolecular reaction is enantioselectively transformed to the oxazole α-hydroxy ester derivatives 4 in quantitative yield and good to excellent enantioselectivity via an asymmetric copper(II)-catalyzed Alder-ene reaction. (Figure presented.).
- Nalivela, Kumara Swamy,Rudolph, Matthias,Baeissa, Elham S.,Alhogbi, Basma G.,Mkhalid, Ibraheem A. I.,Hashmi, A. Stephen K.
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p. 2183 - 2190
(2018/04/30)
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- An Industrial Perspective on Counter Anions in Gold Catalysis: Underestimated with Respect to “Ligand Effects”
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The conversion of a variety of well-known test reactions, representing the key reactivity patterns of gold catalysis, were analyzed by GC and 1H NMR. The study is focused on establishing of a strategical approach for the consideration of ligand
- Schie?l, Jasmin,Schulmeister, Jürgen,Doppiu, Angelino,W?rner, Eileen,Rudolph, Matthias,Karch, Ralf,Hashmi, A. Stephen K.
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p. 2493 - 2502
(2018/04/25)
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- An Industrial Perspective on Counter Anions in Gold Catalysis: On Alternative Counter Anions
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A comparison of versatile counter anions was investigated by means of a variety of well-known test reactions representing the key reactivity patterns of homogeneous gold catalysis, the catalytic activity was monitored by GC and 1H NMR. As previ
- Schie?l, Jasmin,Schulmeister, Jürgen,Doppiu, Angelino,W?rner, Eileen,Rudolph, Matthias,Karch, Ralf,Hashmi, A. Stephen K.
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p. 3949 - 3959
(2018/09/06)
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- Synthesis and characterization of a gold(i) bis(triazolylidene) complex featuring a large [(TpMe2)2K] anion
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In the quest of heteroleptic gold(i) complexes containing triazolylidenes (MIC) and TpMe2 ligands, we discovered that reaction of the MIC-Au-I complex 2 with potassium hydrotris-(3,5-dimethyl-1-pyrazolil) borate (KTpMe2) produces an
- Mendoza-Espinosa, Daniel,Priante-Flores, Armando,Rheingold, Arnold L.,Salazar-Pereda, Verónica
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supporting information
p. 15533 - 15537
(2018/10/04)
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- Synthesis of unnatural α-amino esters using ethyl nitroacetate and condensation or cycloaddition reactions
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We report here on the use of ethyl nitroacetate as a glycine template to produce α-amino esters. This started with a study of its condensation with various arylacetals to give ethyl 3-aryl-2-nitroacrylates followed by a reduction (NaBH4 and then zinc/HCl) into α-amino esters. The scope of this method was explored as well as an alternative with arylacylals instead. We also focused on various [2 + 3] cycloadditions, one leading to a spiroacetal, which led to the undesired ethyl 5-(benzamidomethyl)isoxazole-3-carboxylate. The addition of ethyl nitroacetate on a 5-methylene-4,5-dihydrooxazole using cerium(IV) ammonium nitrate was also explored and the synthesis of other oxazole-bearing α-amino esters was achieved using gold(I) chemistry.
- Gagnot, Glwadys,Hervin, Vincent,Coutant, Eloi P.,Desmons, Sarah,Baatallah, Racha,Monnot, Victor,Janin, Yves L.
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supporting information
p. 2846 - 2852
(2018/11/27)
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- Merging gold catalysis, organocatalytic oxidation, and Lewis acid catalysis for chemodivergent synthesis of functionalized oxazoles from: N -propargylamides
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Novel catalytic systems consisting of cationic gold complexes, N-hydroxyphthalimide (NHPI), and transition-metal-based Lewis acids have been developed for the one-pot synthesis of functionalized oxazoles from N-propargylamides with excellent functional group tolerance. These transformations demonstrated the excellent compatibility of homogeneous gold catalysis with organocatalytic oxidative carbon-nitrogen bond formations using tert-butyl nitrite as the terminal oxidant. Moreover, oxazolecarbonitriles or carboxamides can be easily synthesized in a one-pot protocol according to the different synthetic requirements.
- Mai, Shaoyu,Rao, Changqing,Chen, Ming,Su, Jihu,Du, Jiangfeng,Song, Qiuling
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p. 10366 - 10369
(2017/09/25)
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- Predicting Counterion Effects Using a Gold Affinity Index and a Hydrogen Bonding Basicity Index
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We have developed a gold affinity index and hydrogen bonding basicity index for counterions and have used these indexes to forecast their reactivity in cationic gold catalysis.
- Lu, Zhichao,Han, Junbin,Okoromoba, Otome E.,Shimizu, Naoto,Amii, Hideki,Tormena, Cláudio F.,Hammond, Gerald B.,Xu, Bo
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supporting information
p. 5848 - 5851
(2017/11/10)
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- An ambiphilic phosphine/H-bond donor ligand and its application to the gold mediated cyclization of propargylamides
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We describe the synthesis of an ambiphilic phosphine/H-bond donor ligand featuring a trifluoroacetamide functionality, its coordination to gold(i) chloride, and its application as a self-activating catalyst for the cyclization of propargylamides.
- Sen, Srobona,Gabba?, Fran?ois P.
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supporting information
p. 13356 - 13358
(2017/12/26)
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- Readily switchable one-pot 5-exo-dig cyclization using a palladium catalyst
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A convenient, ligand-free, Pd(OAc)2-catalyzed one-pot reaction has been developed for the synthesis of oxazolines and oxazoles from easily available acid chlorides and propargylamine. The reaction pathways could be easily modulated to selectively obtain oxazolines or oxazoles by merely changing the additives. This method proceeds via in situ sequential nucleophilic addition/elimination reactions followed by an intramolecular 5-exo-dig cycloisomerization reaction. An interesting observation in this case is the effect of an additive: a basic additive such as triethylamine resulted in the formation of 5-methylene oxazolines, while an acidic additive such as acetic acid resulted in the formation of 5-methyloxazoles. With the current protocol we are able to obtain good to moderate yields of the desired product without the need for the isolation of intermediates.
- Mali, Jaishree K.,Takale, Balaram S.,Telvekar, Vikas N.
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p. 2231 - 2235
(2017/01/22)
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- Synthesis, Structure and Catalytic Activity of NHC–AgICarboxylate Complexes
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A general synthetic route was used to prepare 15 new N-heterocyclic carbene (NHC)–AgIcomplexes bearing anionic carboxylate ligands [Ag(NHC)(O2CR)], including a homologous series of complexes of sterically flexible ITent ligands, which permit a systematic spectroscopic and theoretical study of the structural and electronic features of these compounds. The complexes displayed a significant ligand-accelerated effect in the intramolecular cyclisation of propargylic amides to oxazolidines. The substrate scope is highly complementary to that previously achieved by NHC–Au and pyridyl–AgIcomplexes.
- Wong, Valerie H. L.,Vummaleti, Sai V. C.,Cavallo, Luigi,White, Andrew J. P.,Nolan, Steven P.,Hii, King Kuok Mimi
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supporting information
p. 13320 - 13327
(2016/09/09)
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- Triaryl-Like MONO-, BIS-, and TRISKITPHOS Phosphines: Synthesis, Solution NMR Studies, and a Comparison in Gold-Catalyzed Carbon-Heteroatom Bond Forming 5-exo-dig and 6-endo-dig Cyclizations
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A homologous series of triaryl-like KITPHOS-type monophosphines containing one, two, or three bulky 12-phenyl-9,10-dihydro-9,10-ethenoanthracene (KITPHOS) units have been developed, and the influence of increasing steric bulk on their efficacy as ligands in gold(I)-catalyzed carbon-heteroatom bond-forming cyclizations has been investigated. Detailed solution NMR studies on Ph-TRISKITPHOS, its oxide, and the corresponding gold(I) chloride adduct identified a conformational exchange process involving a concerted librational motion of the individual anthracene-derived organic substituents about their P-C bonds. The cessation of this motion at reduced temperatures lowers the molecular symmetry such that the two C6H4 rings in each of the KITPHOS units become inequivalent; a lower energy process involving restricted rotation of the biaryl-like phenyl ring has also been identified. Electrophilic gold(I) complexes of these triaryl-like KITPHOS monophosphines catalyze the 5-exo-dig cycloisomerization of propargyl amides to afford the corresponding methylene oxazolines, which were used in a subsequent tandem carbonyl-ene reaction to afford functionalized 2-substituted oxazolines. A comparative survey revealed that catalyst efficiency for cycloisomerization decreases in the order MONOKITPHOS = BISKITPHOS > PPh3 > TRISKITPHOS. The optimum system also catalyzes the selective 6-endo-dig cyclization of 2-alkynylbenzyl alcohols, 2-alkynylbenzoic acid, and 2-phenylethynyl benzamides; gratifyingly, in several cases the yields obtained are markedly higher and/or reaction times significantly shorter than those previously reported for related gold catalysts. Moreover, these are the first examples of gold(I)-catalyzed 6-endo-dig cycloisomerizations involving 2-phenylethynyl benzamides and, reassuringly, the optimum gold(I)/MONOKITPHOS systems either rivaled or outperformed existing silver or palladium-based catalysts. The steric parameters of this homologous series of phosphines have been quantified and compared with selected triarylphosphines using a combination of Solid-G calculations, to determine the percentage of the metal coordination sphere shielded by the phosphine (the G parameter), and Salerno molecular buried volume calculations (SambVca) to determine the percent buried volume (%Vbur); the corresponding Tolman cone angles have also been determined from correlations.
- Doherty, Simon,Knight, Julian G.,Perry, Daniel O.,Ward, Nicholas A. B.,Bittner, Dror M.,McFarlane, William,Wills, Corinne,Probert, Michael R.
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supporting information
p. 1265 - 1278
(2016/06/01)
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- Safe and Fast Flow Synthesis of Functionalized Oxazoles with Molecular Oxygen in a Microstructured Reactor
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The synthesis of hydroperoxymethyl oxazoles by oxidation of alkylideneoxazoles with molecular oxygen was implemented in a microstructured reactor for increased safety and larger-scale applications. Elaborate studies on the influence of pressure and temper
- Bay, Sarah,Baumeister, Tobias,Hashmi, A. Stephen K.,R?der, Thorsten
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p. 1297 - 1304
(2016/07/23)
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- Stable yet reactive cationic gold catalysts with carbon based counterions
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L-Au-[TsC(CN)2] are new cationic gold catalysts with a carbon based counterion, which are widely applicable for gold catalyzed reactions. For reactions which need highly reactive gold catalysts, a Lewis acid co-catalyst can be added to increase
- Zeng, Xiaojun,Liu, Shiwen,Xu, Bo
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p. 77830 - 77833
(2018/06/22)
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- Cyclization of 2-Alkynyldimethylaniline on Gold(I) Cationic and Neutral Complexes
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The cyclization reaction of 2-(1-hexynyl)dimethylaniline (S) on gold(I) has been studied by NMR spectroscopy, in order to characterize the ion pair structure of the product, [LAuSc]BF4. The latter is a good model for the catalytic in
- Biasiolo, Luca,Belpassi, Leonardo,Gaggioli, Carlo Alberto,MacChioni, Alceo,Tarantelli, Francesco,Ciancaleoni, Gianluca,Zuccaccia, Daniele
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p. 595 - 604
(2016/03/04)
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- Mono- and digold(I) complexes with mesoionic carbenes: Structural characterization and use in catalytic silver-free oxazoline formation
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Triazolylidenes are a prominent class of mesoionic carbenes that have found use as supporting ligands in homogeneous catalysis in recent years. We present here the syntheses of three new mononuclear gold(I) chlorido and two new dinuclear gold(I) chlorido complexes. The ligands in the aforementioned complexes are derived from either the corresponding monotriazolium or the bitriazolium salts. All complexes have been characterized by 1H and 13C{1H} NMR spectroscopy, mass spectrometry, and single-crystal X-ray diffraction studies. Structural characterization delivers a delocalized bonding situation within the triazolylidene ligands and a linear coordination at the gold(I) centers. The gold(I) centers in all cases are bound to one triazolylidene-C donor and a chlorido ligand. Additionally, for the digold(I) complexes large Au-Au distances were observed, ruling out the existence of aurophilic interactions in these digold complexes in the solid state. All of the gold(I) complexes were tested as (pre)catalysts for the cyclization reaction of propargylic amides to form oxazolines. We show here that the steric bulk of the substituents on the triazolylidene ligands plays a decisive role in the catalytic efficiency of the gold(I) complexes. Copper(II) triflate is shown as a viable alternative to silver(I) salts as an additive for the oxazoline formation. Mechanistic studies show the detection of a gold(I) triazolylidene vinyl complex as an intermediate in the catalytic synthesis of oxazoline with these complexes. These results thus establish copper(II) triflate as an alternative to silver(I) salts as an additive in gold(I) triazolylidene catalysis. Furthermore, it also shows that steric tuning of triazolylidene ligands can indeed be utilized for increasing the catalytic efficiency of the corresponding complexes.
- Hettmanczyk, Lara,Schulze, Dennis,Suntrup, Lisa,Sarkar, Biprajit
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p. 3828 - 3836
(2016/12/07)
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- Acidic Co-Catalysts in Cationic Gold Catalysis
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A systematic study on the effects of Lewis or Br?nsted acid co-catalysts in gold-catalyzed reactions was undertaken using representative reactions (O-, N-, and C-nucleophilic additions to alkynes). Through these reactions, it was demonstrated that an acidic co-catalyst can increase the catalyst turnover significantly, enabling practical reaction rates at competitive catalyst loadings (1 mol %). Further investigation is currently underway to improve the understanding of the subtle principles underlying these experimental observations.
- Barrio, Pablo,Kumar, Manish,Lu, Zhichao,Han, Junbin,Xu, Bo,Hammond, Gerald B.
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p. 16410 - 16414
(2016/11/09)
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- FeBr3-Catalyzed Tandem Reaction of N -Propargylamides with Disulfides or Diselenides for the Synthesis of Oxazole Derivatives
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A methodology of FeBr3-catalyzed tandem reaction of N-propargylamides with disulfides or diselenides for the formation of oxazole derivatives has been developed. The strategy includes several steps in one pot. Series of N-propargylamides and disulfides were suitable as substrates in this transformation for synthesizing the corresponding oxazole derivatives in moderate to good yields.
- Gao, Xu-Hong,Qian, Peng-Cheng,Zhang, Xing-Guo,Deng, Chen-Liang
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p. 1110 - 1115
(2016/05/19)
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