Facile reductions of nitro-organics and hydroaminations mediated by an Fe(salen) complex Emily Pocock 1 , Ruth Webster 1, Michael Nunn 2 1 University of Bath, UK, 2 Early Chemical Development, AstraZeneca, UK Iron catalysis offers an attractive alternative to the more commonly-used precious metals due to its high abundance and low cost, along with the additional benefits of being a non-toxic and environmentally-benign metal. [1] A large number of transition metal salen complexes have been reported and are capable of mediating lots of organic transformations. [2] Complexes containing these ligands are highly versatile due to the ligand’s modular nature and synthesis scalability. [3] Inspired by this the Webster group successfully demonstrated the ability of iron supported by the ‘most simple’ salen (salen = N,N′-bis(salicylidene)ethane-1,2-diamine) ligand to catalyse both hydrophosphination reactions and more recently, the trimerizations of alkynes and hydroboration of carbonyls. [3],[4],[5] While iron catalysis is becoming prevalent in a 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 and temperatures. [1],[6] 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. [1],[6],[7] 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. [6] Throughout the literature a variety of different methods have been reported for the synthesis of amines including but not limited to the alkylation of ammonia, reduction of nitriles, reduction of amides and reductive amination of carbonyls. [6-7] The limitations associated with these methods mean that the reduction of nitro-compounds offers an alternative and convenient method for accessing functionalised amines.In light of this, herein we report the use of the Fe-salen catalyst alongside a reducing agent for the selective one-step reduction of various nitro-compounds to yield synthetically-important products under mild reaction conditions in short reaction times. Based on our understanding of how the mechanism for pre-activation of the catalyst proceeds and comparison to current literature, we successfully extended the reactivity to one-pot hydroaminations and other highly desirable organic transformations. [7] References 1. K. Zhu, M. P. Shaver and S. P. Thomas, Chem. Sci. , 2016, 7 , 3031-3035. 2. L.Canali, D. Sherrington, Chem. Soc. Rev., 1999, 28 , 85-93. 3. J. K.Gallagher, R. L. Webster, Chem. Commun ., 2014, 50 , 12109-12111. 4. C. Provis-Evans, S. Lau, V. Krewald, R. L. Webster, ACS Catal ., 2020, 10 , 10157-10168. 5. K. Gallagher, M. Espinal-Viguri, M. Mahon, R. L. Webster, Adv. Synth. Catal., 2016, 358 , 2460-2468. 6. C. W. Cheung and X. Hu, Nat. Commun. , 2016, 7 , 12494. 7. J. Gui, C. M. Pan, Y. Jin, T. Qin, J. C. Lo, B. J. Lee, S. H. Spergel, M. E. Mertzman, W. J. Pitts, T. E. La Cruz, M. A. Schmidt, N. Darvatkar, S. R. Natarajan and P. S. Baran, Science , 2015, 348 , 886-891.
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