Protection of the gold (I) Catalyst by AsPh3 in Reactions of Enynes

Abstract

HBHC (Hydrogen Bond supported Heterocyclic Carbene) and NAC (Nitrogen Acyclic Carbene) neutral gold complexes have been synthesized by reaction of isocyanogold derivatives ([AuCl(CNR)] with amines. Cationic complexes [Au(carbene)(AsPh3)](SbF6) have been also prepared. The catalytic activity of both types of complex (for the former AgSbF6 is used to extract the halide) in skeletal rearrangement and methoxycyclization of enynes has been studied. The cationic complexes with AsPh3 are active but slower; as an advantage they do not decompose during the catalysis. In contrast, the catalysts formed in situ from the halide neutral complexes are very fast but undergo decomposition. An interesting trade-off was found by adding sub-stoichiometric amounts of AsPh3 (e.g. 10 mol%) relative to the gold catalyst ([Au(carbene)Cl] + AgSbF6), which prevents or dramatically reduces the decomposition observed. This protecting ligand promises to prevent or minimize undesired decomposition of gold catalysts.