We report the synthesis of nine new N-heterocyclic carbene gold bifluoride complexes starting from the corresponding N-heterocyclic carbene gold hydroxides. A new methodology to access N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene gold(I) fluoride starting from N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene gold(I) hydroxide and readily available potassium bifluoride is also reported. These gold bifluorides were shown to be efficient catalysts in the hydrofluorination of symmetrical and unsymmetrical alkynes, thus affording fluorinated stilbene analogues and fluorovinyl thioethers in good to excellent yields with high stereo- and regioselectivity. The method is exploited further to access a fluorinated combretastatin analogue selectively in two steps starting from commercially available reagents.

NHC-derived selenoureas, which are useful for the quantification of NHC electronic properties, are deployed as ligands for Au(I). Surprisingly, while some compounds led to the expected [AuCl(SeUr)] species, selenoureas derived from more π-accepting NHCs unexpectedly furnished crystals of the corresponding [Au(SeUr) 2 ][AuCl 2 ] species, in which ligand rearrangement had occurred.

Novel (NHC)gold(I) hydroxides are reported. Their differing tolerances to air and moisture are rationalized by the varying abilities of the NHC ligands to sterically protect the reactive metal center. A number of gold hydroxides were used in the silver-free preparation of Gagosz-type catalysts. This general procedure led to analytically pure products while avoiding the use of expensive silver reagents.

A novel route for the large-scale synthesis of [Au(NHC)(OH)] complexes is reported. Using this new methodology, several [Au(NHC)(OH)] complexes were readily and efficiently accessed on multi-gram scale (up to 20 g)

SummaryThe role of silver additives is examined in the context of gold-mediated functionalisation of aromatic C–H bonds. Doubt is cast on the commonly cited route of halide abstraction from gold and evidence of substrate activation is given.