The current work describes a methodology for the reduction of carboxylic acids by using a Ni(0) source, diphosphines, and hydrosilanes as the reducing agents. Initial catalytic activity assessment of the nickel dimer [(dippe)Ni(µ-H)]2, towards the reduction of benzoic acid (BA) as model substrate, was proved unsuccessful. Mainly due to protonation of the dimer by the BA, and subsequent formation of inert species [(dippe)Ni(µ-H)]2H, identified by its characteristic 31P NMR shifts. The use of 1:1 mixtures of Ni(cod)2 and diphosphines, yields a conversion of BA up to 87%. Aside the direct reduction products, namely the alcohol, aldehyde and alkane, silylated reduction products could be detected by GC-MS analysis. Further acidic workup enables obtention of the corresponding alcohol and/or aldehyde. The use of a higher number of equivalents of phenylsilane showed a little increase in conversion, with a concomitant increase of disproportion products such as Ph2SiH2 and Ph3SiH. The presence of the bis-benzyloxy product is indicative of the need of two hydride units from the silane. This can also explain the lack of activity with the use of triethyl silane. More silanes, including TMDS are to be tested, as well as other nickel sources and diphosphines.

Nickel catalyzed hydrosilylation of carboxylic acids

2019 Fall National Meeting

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