We report the use of cationic gold complexes [Au(NHC)(CH3CN)][BF4] and [{Au(NHC)}2(μ–OH)][BF4] (NHC = N-heterocyclic carbene) as highly active catalysts in the solvent-free hydroalkoxylation of internal alkynes using primary and secondary alcohols. Using this simple protocol, a broad range of (Z)-vinyl ethers were obtained in excellent yields and high stereoselectivities. The methodology allows for the use of catalyst loadings as low as 200 ppm for the addition of primary alcohols to internal alkynes (TON = 35 000, TOF = 2188 h–1).

Thei mproved synthesis of g-, d-a nd elactones using ad inuclear N-heterocyclic carbene (NHC)-gold(I) catalyst is reported. This solventfree process provides access to g-a nd d-lactones in high regio-and stereoselectivity.R eactions were performed at low catalyst loadings andw ithout the need for any additives.T he use of adigold pre-catalyst providesanew synthetic route to functionalised e-lactones,p oorly accessible using previous methodologies.

ABSTRACT:The synthesis and isolation of gold (I)

ABSTRACT:The role of counterions in chemistry mediated by gold complexes stretches much further than merely providing charge balance to cationic gold species. Interplay between their basicities and coordination strengths influences interactions with both the gold center and substrates in catalysis. Actual monogold(I) active species are generally believed to be mono-coordinated species, formed from the abstraction or the decoordination of a second ligand from precursor complexes, but only little experimental evidence exists to underpin the existence of these transient species. The formation of a bench-stable neutral IPr Cl -gold(I) tetrafluoroborate complex is herein reported. Experimental studies by X-ray diffraction analysis, NMR spectroscopy and theoretical studies by DFT calculations were conducted to determine the composition, structure, and behavior of this complex. The absence of an auxiliary ligand resulted in inner-sphere coordination of the counterion in the solid state. In solution, an equilibrium between two conformations was found with the counterion occupying inner-sphere and outer-sphere positions, respectively. Stoichiometric and catalytic reactivity studies with the tetrafluoroborate complex have been conducted. These confirmed the lability of the inner-sphere coordinating counterion that gives the IPr Cl -gold(I) fragment similar behavior to related systems.

A well-defined NHC–gold(i) complex has been shown highly effective in the formation of ethers from secondary benzylic alcohols and phenols under mild reaction conditions.