Selective Nitrile Reduction

Nitrile reduction usually needs stoichiometric amounts of metal hydrides or hydrosilanes, which are environmentally unfriendly. The hydrogenation of nitriles has also been developed, but it suffers from several problems, e.g., a need for precious metals as catalysts, low selectivity, and limited substrate scope. The selective hydrogenation of nitriles to form secondary imines with an environmentally benign catalyst is a challenging research goal.

David Milstein, Weizmann Institute of Science, Rehovot, Israel, and colleagues have developed a protocol for the selective hydrogenation of a wide range of (hetero)aromatic and aliphatic nitriles to secondary imines. The team used an iron–PNP pincer complex (pictured) as the catalyst. The reactions were carried out in benzene at 90 °C under 30 bar hydrogen in the presence of the catalyst and tBuOK.

The researchers found that aromatic nitriles were generally hydrogenated in higher yields (up to 97 %) and required 1 to 4 mol % catalyst, but aliphatic nitriles gave lower yields (11 to 69 %) and required 8 mol % catalyst. In contrast to other iron PNP catalysts, no amines were observed.

• Selective Hydrogenation of Nitriles to Secondary Imines Catalyzed by an Iron Pincer Complex,
  Subrata Chakraborty, David Milstein,
  ACS Catal. 2017.
  DOI: 10.1021/acscatal.7b00906

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