A frustrated Lewis pair (FLP) consists of a sterically encumbered combination of Lewis acid and base that precludes them from forming an acid-base adduct, therefore ‘frustrating’ their electronic needs. The most significant breakthrough of this relatively young field was the discovery that FLPs can reversibly break the bond of molecular hydrogen, and transfer these hydrogen atoms to another molecule, therefore serving as a new class of reducing agents. Hydrogenation of a series of ketones and aldehydes was achieved under microwave irradiation using catalytic tris(pentafluorophenyl)borane and an ethereal solvent. Several parameters were tested, including hydrogen pressure, solvents, concentration, and catalyst loading. Cyclopentyl methyl ether and 1,4-dioxane showed the best results when reacting with various substrates and 10% catalyst. Reaction times were reduced from days to hours, or even minutes, depending on the substrate under study. These microwave-assisted reactions are significantly faster than similar reactions using conventional heating methods, while producing similar yields. The results presented herein suggest that microwave irradiation can significantly enhance the rate of FLP-catalyzed hydrogenations.

Microwave-assisted hydrogenation of aldehydes and ketones using frustrated Lewis pairs

255th National Meeting (2018)

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