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

Abstract

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.