Copper hydride complexes supported by bis(phosphino)amine ligands have been used in this study. The stoichiometric reactions between (R-PNP)nCu2nH2n (n = 2 or 3, R = iPr, Cy, tBu) complexes and N-Methyl-2-pyrrolecarboxaldehyde under varying conditions have been monitored by 1H and 31P{1H} NMR at room temperature. These results indicate that the reactivity of the hydride depends on the steric environment around the copper hydride moiety. Under H2 atmosphere, the mixtures from the aforementioned stoichiometric reactions slowly generate the alcohol product. In contrast, in-situ generation of copper hydride in the presence of the substrate (N-Methyl-2-pyrrolecarboxaldehyde) generates the alcohol quantitatively as short as in ten minutes. These results suggest that the reactive intermediate is not a multinuclear copper hydride. In the presence of KOtBu, H2 and (iPr-PNP)3Cu6H6, N-Methyl-2-pyrrolecarboxaldehyde has been shown to be converted to the alcohol at a faster rate than the reaction without the base. Preliminary results indicate that only KOtBu increases the rate of hydrogenation. What exact role that the base plays in enhancing the catalytic hydrogenation is an ongoing study.

Effects of nuclearity and added base on copper-catalyzed hydrogenation reactions

ACS Fall 2020 Virtual Meeting

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