Water-soluble gold(I)–NHC complexes of sulfonated IMes and SIMes and their catalytic activity in hydration of alkynes

Synthesis and Application of Water‐Soluble NHC Transition‐Metal Complexes

“…Czégéni et al. however showed that oleum can also be applied in this reaction 51. A different route to arylsulfonate‐functionalized NHCs was presented by Almássy et al., who treated the previously described 4‐sulfonato‐phenylimidazol with 2‐bromoethylsulfonate or propansultone ( L31 / L32 ) 43c.…”

“…Most NHC complexes with arylsulfonate functionalization are synthesized by reaction with Ag 2 O in water and subsequent transmetalation. In comparison to the complex mixtures obtained in the transmetalation of C31 and C32 to Au I ,43c Joó and co‐workers were able to isolate solely mono‐NHC substituted Au I compounds in the cases of C26 b and C28 b by utilizing two equivalents of [Au(tht)Cl] (tht=tetrahydrothiophene) and switching to MeOH/acetone as reaction medium (Scheme ) 51. Roy et al.…”

AgOTf catalyzed hydration of terminal alkynes

“…Use of toxic and environmentally hazardous Hg(II)‐salts for this purpose is a dramatic barrier for the application in laboratory and industry. Other expensive and heavy metals like Ru, Rh, Pt and Au are also used for hydration of alkyne but prohibit their frequent use for laboratory and industrial purpose. Use of concentrated solution of strong acids (H 2 SO 4 , H 3 PW 12 O 40 and CF 3 SO 3 H) is not always fruitful for large scale preparations …”

Room‐Temperature Hydration of Alkynes Catalyzed by Different Carbene Gold Complexes and their Precursors

“…Generally, these NHC‐AuX catalysts are quite effective because of the special electron‐donating and ‐withdrawing ability of the NHC . Although NHC‐AuX catalysts modified by different functional groups on the nitrogen heterocycle and coordinated with different anions (NHC‐AuX, X=Cl,, SbF 6 ,, BF 4 , OTf, or Br 3 ) have been used for the hydration of alkynes, most of these reactions work at high temperatures (e.g., 120 °C for NHC‐AuSbF 6 , 110 °C for NHC‐AuCl, 70 °C for NHC‐AuOTf and MeOH/H 2 O, under reflux for NHC‐AuBr 3 ). If NHC‐Au‐phenolate was used as a catalyst, the hydration reaction could be performed at room temperature.…”