N,C-bound phosphenium cations as main group hydrogenation catalysts
LE3 .A278 2015
Bachelor of Science
The hydrogenation of silyl enol ethers and imines using N,C-bound phosphenium cations as catalysts were investigated both computationally using the Gaussian 03W suite of programs and through syntheses using both the [Mes(NiPr2)P+][AlCl4-] and [Mes(NiPr2)P+][OTf-] phosphenium salts. Based on the results from the computational investigation, it was found that the hydrogenation silyl enol ethers were much more favourable than imine substrates. A mechanism for the hydrogenation of imines and silyl enol ethers was proposed and is consistent with what is proposed for hydrogenation reactions involving frustrated Lewis pairs. For the synthetic investigation a mixture of the phosphenium salt to be tested and the substrate N-benzylidene-tert-butyl imine were combined in a solution of methylene chloride and sparged with hydrogen gas. The hydrogenated products were characterised using boiling point, by 1H NMR spectroscopy, and by IR spectroscopy. Based on these acquired pieces of data, it was determined that the hydrogenation reactions performed in the synthetic investigation were for the most part unsuccessful, although a partial hydrogenation may have occurred based on a signal appearing in the IR spectrum at 3440 cm-1.
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