A Biomass‐Derived Non‐Noble Cobalt Catalyst for Selective Hydrodehalogenation of Alkyl and (Hetero)Aryl Halides

Abstract

Hydrodehalogenation is astraightforwardapproach for detoxifications of harmful anthropogenic organohalidebased pollutants,aswell as removal of halide protecting groups used in multistep syntheses.An ovel sustainable catalytic material was prepared from biowaste (chitosan) in combination with an earth-abundant cobalt salt. The heterogeneous catalyst was fully characterized by transmission electron microscope,X -rayd iffraction, and X-ray photoelectron spectroscopym easurements,a nd successfully applied to hydrodehalogenation of alkyla nd (hetero)aryl halides with broad scope (> 40 examples) and excellent chemoselectivity using molecular hydrogen as ar eductant. The general usefulness of this method is demonstrated by successful detoxification of non-degradable pesticides and fire retardants.M oreover,t he potential of the catalyst as adeprotection tool is demonstrated in am ultistep synthesis of (AE)-peronatin B( alkaloid).Hydrodehalogenation constitutes an important organic transformation where ahalogen atom is formally substituted with ahydrogen atom. It has become an enabling technology for degradation of anthropogenic and environmentally deleterious chemicals into their less noxious congeners.T he former are often produced in industrial processes and can include polyhalogenated organic pollutants (such as,p olychlorodioxins and polychlorophenols), toxic and persistent pesticides,and fire retardants.[1, 2] Furthermore,hydrodehalogenation reactions are often used in organic synthesis for deprotection chemistry,s ince halides can selectively block one of two reaction sites with similar reactivity without strongly influencing the electronics of the system. [2,3] Additionally,s tereoselective hydrodehalogenation of prochiral gem-dihalo-organic compounds affords chiral halo-organic compounds. [4] Hydrodehalogenation reactions have been performed with various methods,s uch as metal-halogen exchange, [2, 5] metal-mediated reduction, [2,6] photochemical reduction, [7] and reductive radical dehalogenation.[8] Some of these reactions are marred by the use of toxic and explosive reagents, production of stoichiometric metal waste,poor selectivity,and low functional-group tolerance.Nevertheless,there has been an intense research interest in developing more efficient and reliable transition-metal-catalyzed hydrodehalogenation processes (mostly involving,Pd, [9] Rh, [10] Ru, [11] Ni, [4,12] and Fe [13] ) using Grignard reagents, [12c,13] alcohol and base, [9a, 10c, 11a,c] hydrides, [4,9b,c, 12b,d,14] formic acid [9h] or its salt, [9e] hydrazine, [9d] and molecular hydrogen. [9c,f,g,10a,b, 11b,12a] Obviously,f rom an ecological perspective,t he later reagent is considered to be the most efficient, clean, and atom-economical reductant. [15] Fort he last decade,t he implementation of cheap,e arth abundant, non-noble metals for (de)hydrogenation reactions has attracted significant interest in homogeneous and heterogeneous catalysis.[16] As acomplement to molecularly defined organometallic complexes,heter...

Hydrodehalogenation of Aryl Halides through Direct Electrolysis

“…Numerous methods have been developed for this reductive process that replaces halogen atoms with hydrogen atoms . Representative reductants employed in this process include metals or low‐valent metal compounds, hydrides,– hydrogen, electron‐rich organic molecules, and alcoholate . These methods, with their own merits and limitations with respect to key measures, such as chemoselectivities and operational costs, are complimentary to each other.…”

Cobalt Entrapped in N,S‐Codoped Porous Carbon: Catalysts for Transfer Hydrogenation with Formic Acid

“…Researchers have been attempting to replace precious metal catalysts with transition metal catalysts. Recently, transition‐metal‐based N‐doped carbon catalysts (M–N–C, M=Co, Fe, Ni) have received worldwide attention, because they exhibit similar properties to those of noble metal catalysts and can promote number of organic reactions . Subsequently, several efficient M–N–C catalysts have been developed for active and selective hydrogenation of functionalized of nitroarenes with FA .…”

Biomass‐Derived N‐doped Carbon Materials with Silica‐Supported Ultrasmall ZnO Nanoparticles: Robust Catalysts for the Green Synthesis of Benzimidazoles

“…The C 1s XPS peaks of ZnO/SiO 2 ‐NC‐600 (Figure c) shows that the lower energy peak near 284.52 eV is assigned to graphitic carbon species or C−N bonds, the peak centered at about 285.13 eV is attributed to C=C bonds, and the higher binding energy 288.43 eV originates from C−C or C−H bonds in undecomposed chitosan . The deconvolution of N 1s energy‐level signals (Figure d) suggests that ZnO/SiO 2 ‐NC‐600 contains several nitrogen species, including intact NH 2 groups (397.74 eV); pyridinic, pyrrolic, and graphitic nitrogen atoms (398.73, 399.72, and 400.70 eV, respectively), and pyridinic N ‐oxide functions (402.01 eV) . In addition, an N 1s signal also appears at 398.13 eV, which falls in the range of the binding energies of N−Zn bonds, thus further verifying that interactions between ZnO nanoparticles and the N‐doped carbon support exist…”

“…When using supported ultrasmall catalysts, the major challenges are the prevention of leaching and aggregation of the nanoparticles from the supports during reactions. To solve these problems simultaneously, N‐doped carbon materials are frequently employed as supports due to the interactions of the nitrogen atoms with such ultrasmall nanoparticles, thus maintaining the stability of the nanoparticles and even enhancing their catalytic activities . For catalytic applications, the development of highly efficient, supported ultrasmall nanoparticles on N‐doped carbon materials continues to have much potential.…”