Low‐Pressure Hydrogenation of Nitriles to Primary Amines Catalyzed by Ruthenium Pincer Complexes. Scope and mechanism

Abstract

The catalytic hydrogenation of nitriles to primary amines constitutes an environmentally benign and atom‐economical methodology in synthetic organic chemistry. However, selective hydrogenation can be challenging, and usually elevated pressure and the use of various additives is required. Herein the hydrogenation of aromatic and aliphatic nitriles to form primary amines catalyzed by ruthenium pincer complexes is described. The reactions are conducted at low H2 pressure, low catalytic loadings and, in case of a variety of benzonitriles, under neutral conditions and without any additives. Mechanistic insight is provided.

Chemoselective hydrogenation of nitriles to primary amines catalyzed by water‐soluble transition metal catalysts

“…The result achieved also in the case of 3‐cyanopyridine (65%, Table , entry 5) is comparable to the yields reached under more severe conditions: 71% at 135 °C and 30 bar with cobalt complex, and 69% at 120 °C and 50 bar with manganese catalyst . Finally, our results for the aliphatic nitriles are comparable with those of many homogeneous catalysts, since reduction of aliphatic nitriles is more difficult than aromatic ones, and are better than those obtained from some ruthenium Pincer complexes (35 to 48%) . The comparison of our catalytic system with other homogeneous noble metal catalysts is also interesting.…”

Recent Advances in Catalysis with Transition‐Metal Pincer Compounds

“…Pincer complexes based on Ru, Mo, W, Co, Mn, and Fe can catalyze the hydrogenation of nitriles. This reaction can generate primary or secondary imines as well as primary, secondary, or tertiary amines.…”

“…In fact, the catalyst is able to transform aromatic and aliphatic nitriles and tolerates several functional groups in short times (3 h). Milstein, on the other hand, has recently explored the catalytic activity of complex 10 b and notes that it is very active for the hydrogenation of aromatic nitriles …”

Phosphines and N‐Heterocycles Joining Forces: an Emerging Structural Motif in PNP‐Pincer Chemistry

“…Although numerous metal complexes with de‐aromatized PNP pincer cores are known nowadays, Milstein's ruthenium hydrido carbonyl derivative 84 , , , , and Kempe's PNP iridium complexes of type 85‐E (E = N, CH), , , stand out due to their efficiency in various catalytic reactions (see Scheme ). All catalytic transformations displayed in Scheme involve proton transfer reactions to and from the respective ligand backbones and frequently follow the mechanism outlined in Scheme .…”