The reduction of nitro-compounds has been a transformation of great synthetic interest throughout the years due to the wide variety of resulting products that can be accessed. In particular, the complete reduction of the nitro moiety to the corresponding amine is of great importance owing to the fact amines are known to be versatile organic building blocks. Amines are prevalent in a range of different industries such as chemical, pharmaceutical, and material. Throughout the years a variety of different methods have been reported for the synthesis of amines including the alkylation of ammonia, reduction of nitriles, reduction of amides and reductive amination of carbonyls. The limitations associated with these methods mean that the reduction of nitro-compounds offers an alternative and convenient method for accessing functionalised amines. Due to its high abundance and low-cost, iron catalysis has been found to offer an attractive alternative to commonly used precious metal catalysts such as palladium. In addition to this iron is also reported to have the lowest environmental impact of these metals due to it being environmentally benign and non-toxic. While iron catalysis is becoming prevalent in a wide range of organic transformations the iron catalysed reduction of nitro-groups is relatively underdeveloped. With current methods often requiring longer reaction times and high catalyst loadings. A large number of transition metal salen complexes have been reported and are capable of mediating lots of organic transformations. Complexes containing these ligands are highly versatile due to the ligand’s modular nature and synthesis scalability. Jacobsen’s catalyst is a key example of this type of complex which has been reported to mediate highly enantioselective epoxidations. Inspired by this the Webster group successfully demonstrated the ability of iron supported by the ‘most simple’ salen ligand to catalyse both hydrophosphination reactions and more recently, the trimerizations of alkynes and hydroboration of carbonyls. Herein we report the use of this catalyst alongside a reducing agent for the selective one step reduction of various nitro-compounds to yield synthetically important products under mild reaction conditions.

Facile reductions of nitro-organics mediated by an Fe(salen) complex

ACS Spring 2022

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