Cobalt-Catalyzed and Lewis Acid-Assisted Nitrile Hydrogenation to Primary Amines: A Combined Effort

Abstract

The selective hydrogenation of nitriles to primary amines using a bench-stable cobalt precatalyst under 4 atm of H is reported herein. The catalyst precursor was reduced in situ using NaHBEt, and the resulting Lewis acid formed, BEt, was found to be integral to the observed catalysis. Mechanistic insights gleaned from para-hydrogen induced polarization (PHIP) transfer NMR studies revealed that the pairwise hydrogenation of nitriles proceeded through a Co(I/III) redox process.

Cobalt–Pincer Complexes in Catalysis

“…As ignificant improvement in the nitrile hydrogenation catalysed by Co-pincer complexes hasb een made by Fout andc oworkers, applying the pincerc atalyst 15. [40] This complex can perform the reactionu nder milder conditions (4 atm H 2 ,1 15 8C, 8h)c ompared to the Milstein system,b ut also in this case an activation with NaHBEt 3 is needed. This system provided the hydrogenation of an umber of aliphatic and aromatic nitrilesi n good to excellent yields to the corresponding primary amines.…”

Cobalt Pincer Complexes for Catalytic Reduction of Carboxylic Acid Esters

“…Cobalt compounds, and here especially cobalt pincer type complexes, have been developed for a number of catalytic transformations such as polymerization, bond‐forming reactions, hydrogenations, transfer hydrogenations, hydrosilylations/hydroborations or N 2 activation . Although cobalt‐based reductions of ketones,, aldehydes , nitriles, or alkenes,,, have been studied, until now, hydrogenation of carboxylic acid esters in the presence of this metal has been scarcely examined…”

Mesoporous Metal–Metalloid Amorphous Alloys: The First Synthesis of Open 3D Mesoporous Ni‐B Amorphous Alloy Spheres via a Dual Chemical Reduction Method

“…Amines are important intermediates in the synthesis of many compounds and fine chemicals. Catalytic hydrogenation of nitriles with hydrogen and catalysts is a practical, green, and atom‐economical method for the synthesis of primary amines . However, obtaining good selectivity is challenging because nitriles are readily hydrogenated to secondary and tertiary amines .…”

“…Catalytic hydrogenation of nitriles with hydrogen and catalysts is a practical, green, and atom-economical method for the synthesis of primary amines. [30,31] However, obtaining good selectivity is challenging because nitriles are readily hydrogenated to secondary and tertiary amines. [32,33] Past reports show that homogeneous catalysts are most successful in obtaining high selectivity for primary amines, [30,34] but applications of conventional homogenous catalysts are limited by the difficulty to collect/recover them after the reaction.…”