Ammonium‐Salt‐Tagged IMesAuCl Complexes and Their Application in Gold‐Catalyzed Cycloisomerization Reactions in Water

Belger, Katrin; Krause, Norbert

doi:10.1002/ejoc.201403153

Cited by 25 publications

(17 citation statements)

References 34 publications

(30 reference statements)

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“…Generally, [AuCl] complexes are inactive in catalysis and dehalogenation is required to activate the complex, especially when using phosphines as a ligand. [51][52][53][54] Surprisingly, using the M 12 L 24 nanospheres, conversion of the substrate was seen at local concentrations of 0.27 M and higher. Moreover, it was observed that the activity of the catalyst increases with the local gold catalyst concentration.…”

Section: L 24 Cagesmentioning

confidence: 93%

Gold Catalysis in (Supra)Molecular Cages to Control Reactivity and Selectivity

2018

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Gold catalysis has experienced a tremendous development over the past decades, and is nowadays widely used in organic synthesis to perform chemical transformations of π‐bond‐containing molecules. Catalyst development has been based mostly on ligand development and counter‐ion strategies. More recently, the encapsulation of gold catalysts in (supra)molecular cages was explored as a new way to control selectivity and reactivity of gold catalysts. In this review, we describe the cages that have been employed as hosts for gold complexes, along with their impact on the catalytic performance. Covalent and supramolecular approaches to encapsulate single metal complexes will be described and the impact on the catalytic performance will be discussed. Also, recent strategies to pre‐organize multiple metal centers will be discussed.

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Section: L 24 Cagesmentioning

confidence: 93%

Gold Catalysis in (Supra)Molecular Cages to Control Reactivity and Selectivity

2018

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“…The next step was to examine the reactivity and recyclability of the new gold catalysts in transformations of unsaturated substrates in bulk water. As benchmark reactions, we selected the cycloisomerization of α‐hydroyallene 30 to 2,5‐dihydrofuran 31 , as well as, the intramolecular lactonization of pent‐4‐ynoic acid 32 to 33 (Scheme ) . Initially, we examined the cyclization of allene 30 in the presence of the 4 NHC‐gold(I) complexes obtained by nucleophilic substitution ( 6 , 9 a , 9 b , 9 c ) under standard conditions (5 mol% catalyst, water, room temperature, 24 h; Table ).…”

Section: Resultsmentioning

confidence: 99%

“…Thus, it appears that a slight leaching and/or decomposition of the catalyst by the acidic reaction medium is taking place . All other β‐CD‐tagged NHC‐gold(I) complexes also show excellent catalytic activity and recyclability in this lactonization, without formation of an alkyne hydration side product …”

Section: Resultsmentioning

confidence: 99%

Sustainable Gold Catalysis in Water Using Cyclodextrin‐tagged NHC‐Gold Complexes

2019

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The synthesis of 10 water-soluble β-cyclodextrin-tagged NHCgold(I) complexes is described. Key steps are nucleophilic substitutions, as well as, copper-(CuAAC)-and ruthenium-(RuAAC)-catalyzed azide alkyne cycloadditions. Whereas the CuAAC reliably affords 1,4-disubstituted 1,2,3-triazoles, the regioselectivity of the RuAAC depends on the structure of the coupling partners. Permethylated cyclodextrin-tagged NHC-gold(I) complexes are soluble both in water and in organic solvents. They show excellent catalytic activity and recyclability in cyclization reactions of functionalized allenes and alkynes in bulk water. The enantioselective cycloisomerization of γand δhydroxyallenes could be achieved with up to 38 % ee. Thus, it is possible to take advantage of the chirality of the cyclodextrin moiety for enantioselective gold-catalyzed transformations.

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“…9,10 Since the first synthesis of a sulfonated NHC-metal complex by Herrmann et al, the number of reports about water-soluble NHC ligands has been increasing steadily. 11 Moreover, we could successfully demonstrate their high stability and recyclability in water. 11,12 More often, an amino group of the final NHC-metal complex is quaternized with a Brønsted acid.…”

Section: Introductionmentioning

confidence: 91%

“…For this purpose, N-heterocyclic carbene (NHC) metal complexes were linked to water-soluble polymers 3,4 or silicabased surfaces 4 and carbohydrates. 11,12 More often, an amino group of the final NHC-metal complex is quaternized with a Brønsted acid. 9,10 Since the first synthesis of a sulfonated NHC-metal complex by Herrmann et al, the number of reports about water-soluble NHC ligands has been increasing steadily.…”

Section: Introductionmentioning

confidence: 99%