An Adaptive Rhodium Catalyst to Control the Hydrogenation Network of Nitroarenes

Abstract

An adaptive catalytic system that provides control over the nitroarene hydrogenation network to prepare a wide range of aniline and hydroxylamine derivatives is presented. This system takes advantage of a delicate interplay between a rhodium(III) center and a Lewis acidic borane introduced in the secondary coordination sphere of the metal. The high chemoselectivity of the catalyst in the presence of various potentially vulnerable functional groups and its readiness to be deployed at a preparative scale illustrate its practicality. Mechanistic studies and density functional theory (DFT) methods were used to shed light on the mode of functioning of the catalyst and elucidate the origin of adaptivity. The competition for interaction with boron between a solvent molecule and a substrate was found crucial for adaptivity. When operating in THF, the reduction network stops at the hydroxylamine platform, whereas the reaction can be directed to the aniline platform in toluene.

PCP Pincer Carbene Nickel(II) Chloride, Hydride, and Thiolate Complexes: Hydrosilylation of Aldehyde, Ketone, and Nitroarene by the Thiolate Complex

“…However, there is no comments about the formation of azoxybenzene, azobenzene, or N -phenylhydroxylamine, which are the intermediate species in the reduction of nitroarene to aromatic amine via two mechanistic routes: direct and condensation (Figure ). ,,, As to the mechanism, the GC–MS of the reaction mixture obtained after heating complex 3 (2.5 mol %), nitrobenzene (0.5 mmol), and PhSiH 3 (1.5 mmol) in toluene at 60 °C for 14 h showed the formation of azoxybenzene as a major peak along with azobenzene, aniline, and nitrobenzene. However, when the catalytic reaction was performed using azobenzene (0.5 mmol), complex 3 (2.5 mmol%), and PhSiH 3 (1.5 mmol) in toluene at 100 °C, no aniline is formed; azobenzene remained unreacted.…”

A Cooperative Rhodium/Secondary Phosphine Oxide [Rh/P(O)nBu2] Template for Catalytic Hydrodefluorination of Perfluoroarenes

“…In contrast to 3‐ n Bu , the rhodium(I) variations 1‐OTf and 1‐H , both deprived of the SPO moiety, showed limited reactivity. Likewise, complexes 10 – 11 , recently reported for adaptive hydrogenation of nitroarenes, have not undergone the anticipated transformation [10e] . On the basis of these results, it seems that a degree of cooperation between rhodium hydride and secondary phosphine oxide is essential for achieving higher conversions.…”

Diazines and Triazines as Building Blocks in Ligands for Metal-Mediated Catalytic Transformations

“…A rhodium-based catalyst ( 64 ) for the selective hydrogenation of nitroarenes in the presence of ketones has also recently been reported . The ligand design relies on an electron-deficient triazine combined with electron rich phosphines and pentamethylcyclopentadienyl (Cp*) units, exerting a push–pull electron density mechanism.…”