Application of (phosphine)gold(I) carboxylates, sulfonates and related compounds as highly efficient catalysts for the hydration of alkynes

Abstract

Abstract The catalytic activity of a series of six gold(I) complexes LAuX (L=Ph3P, X=CO2C2F5, SO3-p-tol, SO3Et, SSO2-p-tol; L=Me3P, (p-tol)3P, X=CO2C2F5), as well as the silver(I) complexes Ph3PAgOC(O)C2F5 and Ph3PAgOS(O)2-p-tol·EtOH, regarding the hydration of 3-hexyne forming 3-hexanone in the presence of BF3·Et2O as a co-catalyst has been investigated. It could be shown that all the gold compounds are catalytically active with (Ph3P)AuOC(O)C2F5 (1) being the most active. Using 1, hydration of 3-hexyne takes place at room temperature and turnover frequencies (TOFs) as high as 3900 h−1 can be reached without any notable catalyst deterioration (MeOH as solvent, 70 °C). The silver complexes on the other hand did not furnish 3-hexanone under reaction conditions. This observation is explained with silver being the stronger acceptor compared to gold which can be derived from the crystal structures of representative examples. An optimization of the co-catalyst concentration showed that with increasing concentration the reaction rate increases significantly reaching saturation at approximately 5 mol%. This indicates that the Lewis acid BF3·Et2O plays a role in several steps of the catalytic cycle. 1 was also successfully employed as a catalyst to react acetic acid with 3-hexyne forming 3-hexene-3-acetate but due to water being present in the glacial acetic acid 3-hexanone was also formed.