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Published December 19, 2018 | Supplemental Material
Journal Article Open

Highly Active Platinum Catalysts for Nitrile and Cyanohydrin Hydration: Catalyst Design and Ligand Screening via High-Throughput Techniques


Nitrile hydration provides access to amides that are indispensable to researchers in chemical and pharmaceutical industries. Prohibiting the use of this venerable reaction, however, are (1) the dearth of biphasic catalysts that can effectively hydrate nitriles at ambient temperatures with high turnover numbers and (2) the unsolved challenge of hydrating cyanohydrins. Herein, we report the design of new "donor–acceptor"-type platinum catalysts by precisely arranging electron-rich and electron-deficient ligands trans to one other, thereby enhancing both the nucleophilicity of the hydroxyl group and the electrophilicity of the nitrile group. Leveraging a high-throughput, automated workflow and evaluating a library of bidentate ligands, we have discovered that commercially available, inexpensive DPPF [1,1′-ferrocenendiyl-bis(diphenylphosphine)] provides superior reactivity. The corresponding "donor–acceptor"-type catalyst 2a is readily prepared from (DPPF)PtCl_2, PMe_2OH, and AgOTf. The enhanced activity of 2a permits the hydration of a wide range of nitriles and cyanohydrins to proceed at 40 °C with excellent turnover numbers. Rational reevaluation of the ligand structure has led to the discovery of modified catalyst 2c, harboring the more electron-rich 1,1′-bis[bis(5-methyl-2-furanyl)phosphino] ferrocene ligand, which demonstrates the highest activity toward hydration of nitriles and cyanohydrins at room temperature. Finally, the correlation between the electron-donating ability of the phosphine ligands with catalyst efficiencies of 2a, 2c, 2d, and 2e in the hydration of nitrile 7 are examined, and the results support the "donor–acceptor" hypothesis.

Additional Information

© 2018 American Chemical Society. Received: October 30, 2018; Published: November 27, 2018. We wish to thank Shenzhen Nobel Prize Scientists Laboratory Project (Grant C17783101), the Gordon and Betty Moore Foundation, the King Faud University of Petroleum and Minerals and Caltech for financial support. Ms. Julie Hofstra is acknowledged for assistance in solving the X-ray structure of 2a–c. We thank Dr. Michael Takase and Mr. Larry Henling for acquiring the X-ray diffraction data for catalysts 2a–c. Dr. Tonia Ahmed, Dr. Arthur Han, and Professor Dr. Søren Kramer are acknowledged for revising the manuscript. The authors declare no competing financial interest. Author Contributions: X.X. and C.X. contributed equally.

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August 19, 2023
October 19, 2023