Water‐Soluble Gold–N‐Heterocyclic Carbene Complexes for the Catalytic Homogeneous Acid‐ and Silver‐Free Hydration of Hydrophilic Alkynes

Abstract

Water-soluble gold(III/I) N-heterocylic carbene complexes behave as efficient catalysts for the hydration of terminala lkynes in neat water. Thet ransformation proceeds in the absence of Brønsted acids or halide scavengers and is suitable for sensitive substrates.K inetic profiles and DFT studies provide ac lear pictureo fi ntermediates present during catalysis.

Permethylated NHC‐Capped α‐ and β‐Cyclodextrins (ICyDMe) Regioselective and Enantioselective Gold‐Catalysis in Pure Water

“…The b-CD-de- rived catalyst 5b appeared more activet han the a-CD-based 5a,l eading to complete conversion and quantitative NMR yield after 14 h. This result is similar to that reported for the hydration of 7 in neat water using ammonium-tagged watersoluble NHC-gold complexes at the same catalyst loading (0.5 mol %). [27] The alkyne 8 reacted slowly at 20 8Cw ith both 5a and 5b as gold catalysts, to give 12 in 8-10 %y ield after 24 hu nder similar conditions (data not shown). Increasing the temperature to 50 8Cw as necessary to obtain the bis-deuterated ketone 12 in 88-95% yields (Table 1, entries 3-4).…”

“…The results are summarized in Table 1. At 20 °C, both gold complexes (α‐ ICyD Me )AuCl 5α and ( β‐ICyD Me )AuCl 5β (0.5 mol %) were found to allow efficient hydration [43] of water‐soluble substrate 5‐hexyn‐1‐ol 7 without pre‐activation of the catalyst by a silver salt, [27, 44] to give the corresponding bis‐deuterated methyl ketone 11 in 92–99 % yields (Table 1, entries 1–2). The β‐CD‐derived catalyst 5β appeared more active than the α‐CD‐based 5α , leading to complete conversion and quantitative NMR yield after 14 h. This result is similar to that reported for the hydration of 7 in neat water using ammonium‐tagged water‐soluble NHC‐gold complexes at the same catalyst loading (0.5 mol %) [27] .…”

“…[14,17] Furthermore, the increasing importance of N-heterocyclicc arbenes (NHC) as ligandsh as induced increasing efforts to develop hydrophilic NHCs for metal-basedc atalysis in aqueousm edia, [18][19][20][21][22] and medicala pplications. [23] Ionic salt-tagged NHC ligands have been designed for gold-catalyzed alkyne hydration, [24][25][26][27] cycloisomerization reactions, [26,[28][29][30] and copper-catalyzed azidealkyne cycloadditions (CuAAC). [31,32] Although, water-soluble silver-NHCs have been described since 2004 as antibacterial agents, [33] they have mainly been used as carbene transfer agents, [24,34] and their application in homogeneous catalysis in water remains underexplored.…”

“…At 20 8C, both goldc omplexes( a-ICyD Me )AuCl 5a and (b-ICyD Me )AuCl 5b (0.5mol %) were found to allow efficient hydration [43] of water-soluble substrate 5hexyn-1-ol 7 without pre-activationo ft he catalystb yas ilver salt, [27,44] to give the corresponding bis-deuterated methyl ketone 11 in 92-99 %y ields (Table 1, rived catalyst 5b appeared more activet han the a-CD-based 5a,l eading to complete conversion and quantitative NMR yield after 14 h. This result is similar to that reported for the hydration of 7 in neat water using ammonium-tagged watersoluble NHC-gold complexes at the same catalyst loading (0.5 mol %). [27] The alkyne 8 reacted slowly at 20 8Cw ith both 5a and 5b as gold catalysts, to give 12 in 8-10 %y ield after 24 hu nder similar conditions (data not shown). Increasing the temperature to 50 8Cw as necessary to obtain the bis-deuterated ketone 12 in 88-95% yields (Table 1, entries 3-4).…”

Efficient [(NHC)Au(NTf2)]-catalyzed hydrohydrazidation of terminal and internal alkynes

“…Cationic gold complexes with weakly coordinating counterions (which are often considered to be solvent-separated ions) [1][2][3], render powerful catalysts for the transformation of organic substrates [4][5][6], specifically the reactions of alkynes with a variety of heteroatom nucleophiles (Scheme 1) [7] such as water or alcohol [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22], primary or secondary amines [23][24][25][26][27][28], or hydrazine [29][30][31]. These reactions are synthetically useful since gold catalysis is characterized by a good functional group tolerance for oxygen and nitrogen-containing molecules, which tend to be more difficult for catalytic transformations utilizing other transition metals [32][33][34][35][36].…”