Pd-Catalyzed Transfer Hydrogenation of Alkenes Using Tetrahydroxydiboron as the Sole Hydrogen Donor

Abstract

Tetrahydroxydiboron-mediated catalytic transfer hydrogenations have typically involved co-additives that, like tetrahydroxydiboron itself, are H atom donors. Herein we report an alkene transfer hydrogenation method with tetrahydroxydiboron as the sole source of H atoms. The reaction uses Pd(OAc)₂ as a convenient putative colloid pre-catalyst, and cyclic monoethers are competent solvents. Highly efficient alkene deuteration is demonstrated using tetradeuteroxydiboron.

Key words

tetrahydroxydiboron - transfer hydrogenation - palladium catalysis - alkene reduction - deuterium - catalytic hydrogenation

Publication History

Received: 06 June 2024

Accepted after revision: 03 July 2024

Accepted Manuscript online:
16 July 2024

Article published online:
14 August 2024

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• 20 General Transfer Hydrogenation Procedure An oven-dried one-dram disposable borosilicate vial is charged with a magnetic stir bar, 58.3 mg of tetrahydroxydiboron (0.65 mmol, 1.3 equiv), 2.3 mg of Pd(OAc)₂ (0.01 mmol, 0.02 equiv), and substrate if solid (0.5 mmol, 1.0 equiv). The vial is capped and purged with argon or nitrogen gas, then charged with 1.7 mL of degassed anhydrous THF and heated to 60 °C for 6 h with stirring at 600 rpm. After cooling to ambient temperature, the solution is filtered through a plug of silica gel and rinsed with dichloromethane.
• 21 Characterization Data of Representative Product 2a Yield (0.5 mmol scale): 88 mg (97%), colorless solid. ¹H NMR (400 MHz, CDCl₃): δ = 7.29–7.25 (m, 4 H), 7.21–7.16 (m, 6 H), 2.92 (s, 4 H). ¹³C NMR (100 MHz, CDCl₃): δ = 142.1, 128.6, 128.4, 126.0, 38.0.
• 22 A version of this manuscript was deposited on ChemRxiv prior to review: Yaghoubi M, Reyes IC, Stokes BJ. ChemRxiv 2024; preprint DOI: 10.26434/chemrxiv-2024-k2qdm.