Reactions with High Turnover Numbers and Frequencies

Reactions with High Turnover Numbers and Frequencies 

The status for homogeneous catalysis by gold in solution was dramatically transformed in 1998 by the results of Teles et al.11 This BASF group described the use of cationic Au1 complexes of the type [L-Au+] (where L is a phosphane, phosphite or arsine) for the addition of alcohols to alkynes in the presence of a Lewis or Brpnsted acid as a co-catalyst in methanol at 313 K. An example of such a reaction is the conversion of 3-hexyne to 3,3-dimethoxyhexane  

The turnover numbers for this type of reaction are up to 2 x 105 moles of product per mole of catalyst, with turnover frequencies of up to 5400 h-1. 

These gold catalysts are a significant improvement on the mercury catalysts used previously and the reactions are conducted under mild conditions (293-323 K) in the presence of acid co-catalysts. 2-Propynol reacts with excess methanol at 328 K in the presence of 0.01 mol% CH3Au PPh3 and sulfuric acid to give the following dioxane derivative, f -2,5-dimethyl-2,5-dimethoxy-l,4-dioxane, in 93% yield after 20h at 328 K  

Subsequently, TOFs of 3900 h-1 have been reported12 for the hydration of 3-hexyne at 343 K in aqueous methanol using Ph3PAuI0C(0)C2Fs as catalyst with BF3 -Et20 as co-catalyst to give 3-hydroxy-3-hexene and 3-hexanone  

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