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,heterogeneous mat...

Biomass‐Derived Catalysts for Selective Hydrogenation of Nitroarenes

“…[7] Furthermore, chitosan has become an attractive precursorf or the preparation of nitrogen-doped carbonaceous materials upon hydrothermal treatment followed by calcination, [8] and chitosanw as ap recursor to nitrogen-doped graphene [9] and other nitrogen-doped carbon materials. [11] The resulting powders were characterizedb y am ultitude of analytical techniques including HR-STEM, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). [5,10] Considering these characteristics of chitosan, we recently becamei nterested in preparing cobalt-based heterogeneous materials upon pyrolysis of metal absorbed chitosan, namely, Co(OAc) 2 -chitosan chelate, [7a] at various temperatures (Scheme 1).…”

“…[10] These solid supports have potential applicationsi nv arious fields, such as electrocatalysis and energy storageamong others. [11] As ar epresentative example, the material prepared from Co(OAc) 2 -chitosan at 700 8Ci sc omposed of three different types of cobalt particles:m etallic cobalt,c obalt oxides, and cobalt particlesw ith am etallic core and an oxide shell. [11] The resulting powders were characterizedb y am ultitude of analytical techniques including HR-STEM, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD).…”

“…[11] The resulting powders were characterizedb y am ultitude of analytical techniques including HR-STEM, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). [11] Aromatic amines are key building units for many fine chemicals including pharmaceuticals, agrochemicals, dyes and bulk chemicals. All of these particles are embedded in the carbon matrix.…”

“…[5,10] Considering these characteristics of chitosan, we recently becamei nterested in preparing cobalt-based heterogeneous materials upon pyrolysis of metal absorbed chitosan, namely, Co(OAc) 2 -chitosan chelate, [7a] at various temperatures (Scheme 1). [11] The resulting powders were characterizedb y am ultitude of analytical techniques including HR-STEM, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). [11] As ar epresentative example, the material prepared from Co(OAc) 2 -chitosan at 700 8Ci sc omposed of three different types of cobalt particles:m etallic cobalt,c obalt oxides, and cobalt particlesw ith am etallic core and an oxide shell.…”

“…[11] The resulting powders were characterizedb y am ultitude of analytical techniques including HR-STEM, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). [11] As ar epresentative example, the material prepared from Co(OAc) 2 -chitosan at 700 8Ci sc omposed of three different types of cobalt particles:m etallic cobalt,c obalt oxides, and cobalt particlesw ith am etallic core and an oxide shell. All of these particles are embedded in the carbon matrix.…”