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

The water-soluble carbene ligand precursors sIMesH(+)Cl(-) and sSIMesH(+)Cl(-) were synthesized in high yields by direct sulfonation of IMesH(+)Cl(-) (1,3-bis(2,4,6-trimethylphenyl) imidazolium chloride) and SIMesH(+)Cl(-) (1,3-bis(2,4,6-trimethylphenyl)imidazolinium chloride). Gold(I)-N-heterocyclic carbene complexes [AuCl(sIMes)] and [AuCl(sSIMes)] were prepared by carbene transfer from the zwitterionic [Ag(sIMes)(2)] and [Ag(sSIMes)(2)] to [AuCl(tht)] (tht = tetrahydrothiophene). In methanol-water mixtures or in neat water, the new gold(I)-NHC complexes showed high catalytic activity in Markovnikov type hydration of terminal alkynes (up to a turnover frequency 1990 h(-1); ethynyltoluene, 0.1 mol% catalyst) but were markedly less active in case of internal alkynes (TOF =3.6 h(-1) diphenylethyne, 1 mol% catalyst). These new Au(I)-NHC catalysts do not require acid co-catalysts or activation by Ag(I)-additives. (C) 2011 Elsevier B.V. All rights reserved.