Copper hydride complexes have gained attention due to the unique multinuclear structure, high selectivity and mildness in reducing organic molecules. In this study, several copper hydride complexes supported by bis(phosphino)amine ligands have been isolated and characterized. The synthesis of these complexes involve hydrogenolysis of copper tert-butoxide species. In the 1H NMR spectra of the copper hydride complexes, the assignment of the hydride resonances was confirmed by comparing the 1H NMR spectra of the related copper deuteride complexes. The X-ray crystal structures of the copper hydrides show a hexanuclear species (HN(CH2CH2PiPr2)2)3Cu6H6 for the isopropyl derivative and a tetranuclear species (HN(CH2CH2PCy2)2)2Cu4H4 for the cyclohexyl analog. However, in solution the tetranuclear copper hydride slowly isomerizes to a hexanuclear copper hydride (HN(CH2CH2PCy2)2)3Cu6H6. 1H and 31P {1H} NMR spectra of the tert-butyl derivative indicate that it has a tetranuclear core. An NMR study reveals that the isopropyl system also involves tetranuclear-to-hexanuclear isomerization but at a much faster rate. Reactivity of these copper hydrides were also studied. Reduction of carbon dioxide has been carried out with the copper hydride complexes. The resulting copper formate complexes have been isolated and characterized. Catalytic hydrogenation of aldehydes and ketones have been accomplished in good yields with the isopropyl derivative. The mechanistic studies of the catalytic hydrogenation reactions suggest aldehydes or ketones initially insert to the copper hydride and then undergo hydrogenolysis to generate the alcohol instead of going through co-operative elimination.

Synthesis, reactivity and isomerization of multinuclear copper hydrides supported by bis(phosphino)amine ligands

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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