A Reusable Co Catalyst for the Selective Hydrogenation of Functionalized Nitroarenes and the Direct Synthesis of Imines and Benzimidazoles from Nitroarenes and Aldehydes

Abstract

The use of abundantly available transition metals in reactions that have been preferentially mediated by rare noble metals, for example, hydrogenations, is a desirable aim in catalysis and an attractive strategy for element conservation. The observation of novel selectivity patterns with such inexpensive metal catalysts is especially appealing. Herein, we report a novel, robust, and reusable cobalt catalyst that permits the selective hydrogenation of nitroarenes in the presence of highly hydrogenation-sensitive functional groups, as well as the direct synthesis of imines from nitroarenes and aldehydes or ketones in the presence of such substituents. Furthermore, we introduce the first base-metal-mediated direct synthesis of benzimidazoles from nitroarenes and aldehydes. Functional groups that are easy to hydrogenate are again well tolerated.

The Direct Synthesis of Imines, Benzimidazoles and Quinoxalines from Nitroarenes and Carbonyl Compounds by Selective Nitroarene Hydrogenation Employing a Reusable Iron Catalyst

“…Furthermore, we introduce the direct synthesis of quinoxalines from nitroarenes and diketones.Imines are important compounds and have been used extensively as ligands and for the synthesis of materials, fragrances, fungicides, pharmaceuticals and agricultural chemicals . Thus, the development of novel imine synthesis protocols is of high interest . Benzimidazoles and quinoxalines are similarly important as well as the development of protocols for their synthesis.…”

“…[3] Recently,B eller and coworkers could show that heterogeneous catalystsb ased on abundantly availablet ransition metals,s uch as iron [4] and cobalt, [5] can also mediate the highly selective hydrogenation of nitroarenes.B ased on these initial findings,avariety of groups developed Co catalysts for the selective and efficient hydrogenation of nitroarenes. [6][7][8] Efficient and selective iron catalysts are essentially unknownb eside the initial key contributions. [4] Herein, we report on an ovel reusable andr obust siliconcarbonitrite (SiCN)-based Fe catalyst.…”

“…[11] Thus, the development of novel imine synthesis protocols is of high interest. [7,12,13] Benzimidazoles [7,14] and quinoxalines [15] are similarly important as well as the developmento fp rotocols for their synthesis. We have recently introduced av ariety of SiCN-metal nanocomposite catalysts [16] and have, very recently,i ntroduced highly active,s elective and reusablec obalt catalysts.…”

“…We have recently introduced av ariety of SiCN-metal nanocomposite catalysts [16] and have, very recently,i ntroduced highly active,s elective and reusablec obalt catalysts. [7,8] Our iron nanocomposite catalysth as been synthesized in a two-step procedure. An Fe aminopyridinato complex (Figure 1, top left) and the commercially available polysilazane HTT1800 were dissolved in tetrahydrofuran( THF) and dicumylperoxide (DCP) was added to initiate crosslinking.…”

One‐pot Reductive Amination of carbonyl Compounds with Nitro Compounds by Transfer Hydrogenation over Co–Nx as catalyst

“…[23,24] In our recent work, nitrogen-doped carbon based cobalt catalyst were observedt ob eh ighly active for the reductiono fn itro compounds into primary amines. [23,24] In our recent work, nitrogen-doped carbon based cobalt catalyst were observedt ob eh ighly active for the reductiono fn itro compounds into primary amines.…”