Phosphate ligands in the gold(i)-catalysed activation of enynes

Abstract

Gold(I) forms neutral complexes with binol phosphates that are unreactive in the catalytic cyclisation of enynes. Reaction in protic solvents or activation by silver(I) restores the catalytic activity.

Unexpected Anion Effect in the Alkoxylation of Alkynes Catalyzed by N‐Heterocyclic Carbene (NHC) Cationic Gold Complexes

“…As the pre-equilibrium is completely shifted toward the ISIP in absence of methanol (see the Supporting Information), we can surmise that methanol may help the de-coordination of the anion, probably through the formation of a hydrogen bond. [23] The importance of the pre-equilibrium step is demonstrated by the fact that the addition of an external salt, such as NBu 4 OTs (5 %), reduces the TOF to 4.8 min À1 , probably because of the shift of the ISIP/OSIP equilibrium toward the ISIP.…”

Anion‐Induced Enantioselective Cyclization of Diynamides to Pyrrolidines Catalyzed by Cationic Gold Complexes

“…[17] We could show that such catalysts are indeed active for the intended cycloisomerization ( phosphate complexes (L = PPh 3 , R = SiPh 3 ) were reported by Echavarren and co-workers to react with 1,6-enynes to form stable gold acetylides which did not undergo cycloisomerization. [18] Potentially, also in our case of diynamides 3, gold acetylides may be formed, but reversible protonation by the p-tosylamide moiety might be responsible for restoring the observed catalytic activity.…”

Chiral Phosphate in Rhodium‐Catalyzed Asymmetric [2+2+2] Cycloaddition: Ligand, Counterion, or Both?

“…The question of the interaction between [ I ] + and [( S )‐TRIP] − remained to be answered. In addition to conductivity measurements and IR and 1D NMR spectroscopy, a powerful tool to evidence ion pairing is diffusion ordered spectroscopy (DOSY). This technique has been extensively used by the groups of Pregosin and Macchioni to study cationic organometallic species .…”

“…However, this does not mean that such bonds remain covalent or undergo solvation during catalysis. For instance, although the phosphate–gold complexes A and B were proved to be covalent in CD 2 Cl 2 (Figure ), the phosphate moiety is believed to be a “true” counterion in catalysis due to the linear geometry of the [(R 3 P)Au(substrate)] + complex C , which imposes the phosphate keeping off the coordination sphere of the metal to allow substrate activation . This reasoning based on geometrical constraints cannot be so obviously applied with metal ions of Ir, Pd, Cu, Ru, or Rh .…”