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A Zintl Cluster for Transition Metal-Free Catalysis: C=O Bond Reductions

Bono van IJzendoorn, Saad F. Albawardi, Inigo J. Vitorica-Yrezabal, George F. S. Whitehead, John E. McGrady* and Meera Mehta*

*University of Oxford, Mansfield Road, Oxford, OX1 3QR; University of Manchester, Oxford Road, Manchester, M13 9PL, U.K., Email:,

B. van IJzendoorn, S. F. Albawardi, I. J. Votorica-Yrezabal, G. F. S. Whitehead, J. E. McGrady, M. Mehta, J. Am. Chem. Soc., 2022, 144, 21213-21223.

DOI: 10.1021/jacs.2c08559

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A boron-functionalized heptaphosphide Zintl cluster catalyzes a transition metal-free hydroboration of aldehydes and ketones. Moreover, the greenhouse gas carbon dioxide was efficiently and selectively reduced to methoxyborane.

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Synthesis of [Na(18-c-6)]2[BBN-P7]

To a Schlenk flask charged with a stir bar and [Na(18-c-6)]2[HP7] (1.005 g, 1.27 mmol, 1.0 eq.), HBBN dimer (464 mg, 1.90 mmol, 1.5 eq.), THF (40 mL) was added. Gas evolution was observed. The reaction mixture was allowed to stir until no gas evolution was observed, usually around 1h, and a dark orange solution was observed. The mixture was filtered yielding a clear dark orange solution. The solvent was removed under reduced pressure and the residue was washed with toluene (5 x 20mL). The residue was dissolved in THF (5 mL) and filtered yielding a clear dark orange solution. The solution was filtered and removal of volatiles under reduced pressure yielded glassy orange solids. Crystals suitable for X-ray diffraction analysis were obtained through slow diffusion of hexane into a concentrated THF solution. Isolated Yield: 0.817 g, 70% yield.

Catalytic Hydroboration of Ketones/Aldehydes

Ketone/ aldehyde (0.22 mmol, 1.0 eq.) and toluene (25 ÁL, 0.24 mmol) was added to a solution of [Na(18-c-6)]2[BBN-P7] (2 mg, 2.2 Ámol, 0.01 eq.), pinacolborane (28 mg, 32 ÁL, 0.22 mmol, 1.0 eq.) and oDFB (0.5 mL) in a J Young NMR tube. The reaction was allowed to react for 0.5 ľ 72 h. The reaction was monitored by 1H NMR, 11B NMR and 11B{1H} NMR. NMR conv. was determined by integration of the crude 1H NMR spectrum using the toluene as an internal standard (1H δ = 2.31 ppm). The solvent was removed under reduced pressure and the residue was extracted with pentane or toluene. Removal of volatiles or crystallization allowed for the isolation of the hydroboration products.

Key Words

reduction of carbonyl compounds, pinacolborane

ID: J48-Y2022