A Step into an eco‐Compatible Future: Iron‐ and Cobalt‐catalyzed Borrowing Hydrogen Transformation

Quintard, Adrien; Rodríguez, Jean

doi:10.1002/cssc.201501460

Cited by 131 publications

(28 citation statements)

References 36 publications

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“…As shown in Figure 1 To gain insight into the reaction pathway, additional experiments were performed (Scheme S3 (See Supplementary Materials)). A control experiment of acceptorless dehydrogenation of benzyl alcohol revealed that the combination of tBuOK and CoOx@NC-800 is essential for efficient benzaldehyde formation (See Supplementary Materials), which is generally considered the rate-determining step in the coupling of anilines with benzyl alcohols [17,18,57]. Of note is that the dehydrogenation reaction rate is considerably slower, mainly due to the lack of a hydrogen acceptor to drive the reaction equilibrium to the desired aldehyde.…”

Section: Resultsmentioning

confidence: 99%

“…The borrowing hydrogen strategy has been widely applied in organic transformations to construct various C-X (X = C, N, S) compounds in the last decade [17][18][19]. In this context, of particular importance is the N-alkylation of amines with alcohols to synthesize structurally complex primary and/or secondary amine compounds, which represents one of the most straightforward, efficient and eco-friendly methodologies for amine synthesis.…”

Section: Introductionmentioning

confidence: 99%

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Switchable Access to Amines and Imines from Reductive Coupling of Nitroarenes with Alcohols Catalyzed by Biomass-Derived Cobalt Nanoparticles

et al. 2019

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Cobalt nanoparticles modified with N-doped hierarchical porous carbon derived from biomass are found to be a highly efficient, reusable heterogeneous catalyst for the coupling of nitroarenes with alcohols, selectively affording imines and amines via the borrowing hydrogen strategy for the first time. The product selectivity between imine and amine may be precisely tuned by simple alteration of the reaction conditions without changing the catalyst in one reaction system. In this study, a broad set of complex imines and amines was successfully synthesized in good to high yields with various functional groups tolerated for both nitroarenes and alcohols, highlighting the potentially practical utility of the protocol. This heterogeneous catalyst can be easily removed from the reaction medium by external magnet and can be reused at least four times without significant loss in activity and selectivity.Catalysts 2019, 9, 116 2 of 11 achievements, direct synthesis of imines by the coupling of nitroarenes and alcohols with high activity and selectivity via the borrowing hydrogen strategy remains challenging. To date, only a handful of examples enabled by noble metal catalysts (e.g., Pd [46,47], Ru [48], Ir [49], and Au [50,51]) have been reported; however, their catalytic activities and selectivities are rather low and accompanied by limited substrate scopes (Scheme 1b). In addition, the high cost and limited reserve on earth of noble metal catalysts significantly impedes their large-scale industrial application. Notably, no successful direct imine formation from nitroarenes and alcohols catalyzed by heterogeneous base metal catalysts has been described, to the best of our knowledge.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Switchable Access to Amines and Imines from Reductive Coupling of Nitroarenes with Alcohols Catalyzed by Biomass-Derived Cobalt Nanoparticles

et al. 2019

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“…Following associative interactions conform this mechanism; the catalyst was found applicable in both transfer and pressure hydrogenation [20,25,26], Oppenauer oxidation [27], reductive amination [28], water-gas-shift-reactions [29], electro-reductions [30], alkylations [31], photocatalysis [32], and enantioselective dual catalysis typically for allylic alcohols [33][34][35][36][37][38] with formidable results. The capabilities of Knölker-type catalysts in asymmetric catalysis for normal ketones and imines have also been explored [39], however, their performance regarding enantioselectivity are generally found mediocre, as well for the corresponding ruthenium-based complexes (see Figure 1).…”

Section: Introductionmentioning

confidence: 98%

Synthesis and Catalytic Application of Knölker-Type Iron Complexes with a Novel Asymmetric Cyclopentadienone Ligand Design

et al. 2019

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Asymmetric catalysis is an essential tool in modern chemistry, but increasing environmental concerns demand the development of new catalysts based on cheap, abundant, and less toxic iron. As a result, Knölker-type catalysts have emerged as a promising class of iron catalysts for various chemical transformations, notably the hydrogenation of carbonyls and imines, while asymmetric versions are still under exploration to achieve optimal enantio-selectivities. In this work, we report a novel asymmetric design of a Knölker-type catalyst, in which the C2-rotational symmetric cyclopentadienone ligand possesses chiral substituents on the 2- and 5-positions near the active site. Four examples of the highly modular catalyst design were synthesized via standard organic procedures, and their structures were confirmed with NMR, IR, MS, and polarimetry analysis. Density functional theory (DFT) calculations were conducted to elucidate the spatial conformation of the catalysts, and therewith to rationalize the influence of structural alterations. Transfer- and H2-mediated hydrogenations were successfully established, leading to appreciable enantiomeric excesses (ee) values up to 70%. Amongst all reported Knölker-type catalysts, our catalyst design achieves one of the highest ee values for hydrogenation of acetophenone and related compounds.

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“…[1,2] Thea lcohol is dehydrogenated to ac arbonyl compound, followed by ar eaction with an ucleophile and subsequent reduction with the "borrowed" hydrogen. Due to dwindling crude oil reserves and growingp ublica wareness for the consequences of climate change, the search for alternative carbon resources is getting increasingly urgent.…”

mentioning

confidence: 99%

“…Products 3r and 3s were obtained in 46 and 49 %i solated yield. Considering that the incorporation of primary aliphatic alcohols was possible, we investigated the substrate scope ) 9CoCl 2 2…”

mentioning

confidence: 99%

Cobalt‐Catalyzed Alkylation of Secondary Alcohols with Primary Alcohols via Borrowing Hydrogen/Hydrogen Autotransfer

Freitag

Irrgang

Kempe

2017

Chemistry A European J

118

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Alcohols are promising sustainable startingm aterials because they can be obtained from abundant and indigestible biomass. The substitution of expensive noble metals in catalysis by earth abundant 3d metals,s uch as Mn, Fe, or Co, (nonprecious or base metals) is ar elated key concept with respect to sustainability. Here, we report on the first cobalt-catalyzed alkylationo fs econdary alcohols with primary alcohols. Easy-to-synthesize and easy-toactivate PN 5 P-pincer-ligand-stabilized Co complexes developed in our laboratory mediate the reaction moste fficiently.T he catalysis is applicable to ab road substrate scope and proceeds under relatively mild conditions. We have even demonstrated the coupling of av ariety of purely aliphatic alcohols with ab ase or nonprecious metal catalyst. Mechanistic studies indicatet hat the reactionf ollows the borrowing hydrogen or hydrogen autotransfer concept.The borrowing hydrogen/hydrogen autotransferm ethodology (BH/HA) is ap rominente xample of an alcohol re-functionalization concept. [1,2] Thea lcohol is dehydrogenated to ac arbonyl compound, followed by ar eaction with an ucleophile and subsequent reduction with the "borrowed" hydrogen. Due to dwindling crude oil reserves and growingp ublica wareness for the consequences of climate change, the search for alternative carbon resources is getting increasingly urgent. [3,4] In this regard, alcohols are promising as startingm aterials due to the possibility of obtaining them from abundantlya vailable, indigestible,a nd barely used biomass (lignocellulose). [5][6][7] The direct hetero-coupling of two alcohols follows the BH/HA concept and exclusively uses alcohols as startingm aterials. This reaction has been reported to proceed employing am ultitude of noble metal catalysts.[8] However,n oble metals are rare and their conservation is ak ey issue with regard to as ustainable future.O ne possible approach is the replacemento fp recious metals in key technologies by more abundant metals. Beside Mn, [9] and Fe, [10] especiallyC oc omplexes have been disclosed as highly active and selectivecatalysts for av ariety of reactions following the BH/HA mechanism (see Scheme 1). [11][12][13][14][15][16][17] Iron- [18] and nickel-based [19] homogenousc atalysts have been described for thea lkylation of secondary alcohols by primary alcohols.[20] Unfortunately,t he substrate scopei sl imited, especially for the nickel-catalyzed version. Ab roadly applicable catalyst system based on an onprecious metal,w hich is capable of coupling aromatic, as well as purely aliphatic alcohols remains unknown.Herein, we report on the first cobalt-catalyzed version of the hetero-alkylation of alcohols by alcohols following the BH/HA concept. The catalyst is able to couple substituted 1-phenylethanol derivatives with primary aromatic or aliphatic alcohols as well as secondary aliphatic alcohols with primary aromatic or aliphatic alcohols. Triazine-based PN 5 Pp incer ligand complexesd eveloped in our laboratory are most efficient in these reactions. ...

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A Step into an eco‐Compatible Future: Iron‐ and Cobalt‐catalyzed Borrowing Hydrogen Transformation

Cited by 131 publications

References 36 publications

Switchable Access to Amines and Imines from Reductive Coupling of Nitroarenes with Alcohols Catalyzed by Biomass-Derived Cobalt Nanoparticles

Switchable Access to Amines and Imines from Reductive Coupling of Nitroarenes with Alcohols Catalyzed by Biomass-Derived Cobalt Nanoparticles

Synthesis and Catalytic Application of Knölker-Type Iron Complexes with a Novel Asymmetric Cyclopentadienone Ligand Design

Cobalt‐Catalyzed Alkylation of Secondary Alcohols with Primary Alcohols via Borrowing Hydrogen/Hydrogen Autotransfer

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