Cobalt Complexes Catalyze Reduction of Nitro Compounds: Mechanistic Studies

Abstract

Mononuclear Co 2 + /3 + complexes of 13-membered amide-based macrocycles have been synthesized, characterized and utilized in the chemo-selective reduction of assorted nitro compounds including aromatic, heterocyclic and aliphatic ones. Catalytic results illustrate that Co 3 + complexes are better catalysts than the analogous Co 2 + complexes while mechanistic investigations display the generation of an [(L)Co 2 + (m-NH 2 NH 2 )Co 2 + (L)] intermediate during the catalysis.[a] Dr. Scheme 1. Chemical drawings of cobalt complexes synthesized and studied in this work. In complexes 1 and 2, O' illustrates the coordination of an O amide group from a neighbouring molecule.

Reduction of Nitro Compounds Using 3d-Non-Noble Metal Catalysts

“…Very recently, Gupta and co-workers synthesized two sets of cobalt complexes using tetradentate pyrrolecarboxamido ligands (L3) 435 and amino-amido based macrocycles (L4, Scheme 43). 436 Best results for nitro reductions were obtained when the cobalt in the catalytic pre-cursor was in oxidation state +3 and when electron-withdrawing -Cl groups were present on the aromatic scaffold of the ligands. Cobalt complexes of both L3 and L4 were able to reduce a wide range of nitroaromatics in 6 h using 2 equivalents of hydrazine at 60 °C.…”

“…From a mechanistic point of view, the authors suggested that the peripheral Co(II) are reduced to Co(I) upon addition of hydrazine, thus involving different oxidation states of the cobalt respect to the above described tetradentate ligands. 435,436 On the other hand, the central metal atom is not reduced by hydrazine thus indicating a marginal role in the redox process. This is in line with the very similar results obtained using [Co 2+ -Co 3+ -Co 2+ ] and [Co 2+ -Fe 3+ -Co 2+ ].…”

Catalytic Application of Tactically Aligned Cd(II)‐Based Luminescent 3D‐Supramolecular Networks

“…To the best of our knowledge, so far Cd–CPs have not been investigated for nitro to amine catalytic reduction and this is for the first time we report the use of D‐glucose as the H‐source for the aforementioned reaction under base‐free conditions at RT. The similar state of the art materials and others such as nanoparticles, composites and doped materials were compared with 1 for the sake of the progress of the reported procedure (Table ) . By careful reading of the table, one can easily identify the reduction of nitro to amine utilized drastic conditions such as synthesis of the catalyst, use of noble metals or expansive metals, harsh H‐source such as explosive H 2 or NaBH 4 , hydrazine hydrate, silanes, formats etc.…”

“…The similar state of the art materials and others such as nanoparticles, composites and doped materials were compared with 1 for the sake of the progress of the reported procedure (Table 6). [40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] By careful reading of the table, one can easily identify the reduction of nitro to amine utilized drastic conditions such as synthesis of the catalyst, use of noble metals or expansive metals, harsh H-source such as explosive H 2 or NaBH 4 , hydrazine hydrate, silanes, formats etc. and time of the reaction for the catalysts/amine formation.…”

“…The adsorption method being eco‐friendly, recycling of the dye molecules are preferred over photo degradation and chemical oxidation . Recently, the strategic syntheses of Cd (II)‐CPs have gained much consideration because of their non‐linear optical properties and structural diversity and architectural flexibility also due to the fact that very few reports on Cd (II) based CPs/MOFs have been reported for adsorption and separation of dye molecules …”