The catalytic transfer hydrogenation of ketones is currently recognized as one of the most powerful and valuable synthetic methods for obtaining alcohols, because of its operational simplicity, easy availability of hydrogen sources, lower cost and safety. Furthermore, this process is frequently described in the literature with different homo and heterogeneous catalysts based on Rh, Ir, Ru and Fe. In the same manner, organometallic complexes of nickel have also been used although a lesser extent. To address more “green”, sustainable as well as highly efficient methods for preparing alcohols, we were interested in the investigation of the transfer hydrogenation of simple ketones with nickel catalysts using a primary alcohol as the hydrogen donor and solvent. The results showed that the use of complex Ni(cod)2 in combination with the bidentate phosphine dcype (1,2-bis(dicyclohexylphosphino)ethane) employing ethanol were also highly efficient for the transfer hydrogenation of acetophenone, providing alpha methylbenzyl alcohol to 99% (Table 1, entry 4). The detection of the reaction by using GC showed that the ethanol was converted to ethyl acetate and provided hydride, which reduced ketone (1a) to alcohol (3a). Under the optimal conditions, a variety of alkyl aryl ketones and other ketones were tested to examine the substrate scope with ethanol as hydrogen donor. All tested substrates gave high yields (95-99 %) (Table 2). The substituents on the phenyl ring of substrates or alkylketones such as cyclohexyl ketone (1d) have very little effect on the yield of reaction and the heteroaryl-containing ketones such as 2-furyl methyl ketone (1e) also gave high yield (entry 5).

Efficient nickel-catalyzed transfer hydrogenation of ketones using ethanol as solvent and hydrogen donor

251st National Meeting (2016)

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