Hydrogenation Of Imines Research Articles

Yasunori Okamoto

ChemCatChemVolume 12, Issue 18 p. 4501-4501 InterviewFree Access Yasunori Okamoto First published: 18 August 2020 https://doi.org/10.1002/cctc.202001146AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat Abstract Yasunori Okamoto See the Highly Important Paper in our Young Researchers Series at https://doi.org/10.1002/cctc.202000488 Date of birth: July 22, 1986 Position: Assistant Professor at Tohoku University (Japan) E-mail: yasunori.okamoto@tohoku.ac.jp Homepage: https://researchmap.jp/y_okamoto/?lang=english/ Education: Bachelor in Engineering, Osaka University, Japan (2005–2009) Master in Engineering, Osaka University, Japan (2009–2011) PhD, Osaka University, Japan, under the supervision of Prof. Takashi Hayashi: “Structure-Function Relationship of the Engineered Diiron Active Site in the Hemerythrin-like Domain of a Bacterial Chemotaxis Protein” (2011–2014) Researcher at Okazaki Institute for Integrative Bioscience, Japan, under the supervision of Prof. Shigetoshi Aono (2014) Postdoctoral fellow at the University of Basel, Switzerland, under the supervision of Prof. Thomas R. Ward (2014–2019) Awards: Japan Society for the Promotion of Science Overseas Research Fellow (2017–2019). Research Fellow of the Japan Society for the Promotion of Science (2011–2014) Current research: My current research interests are (1) construction of artificial metalloenzymes, including the development of an abiotic cofactor and (2) multistep chemical transformation enabled by natural/artificial enzymatic reaction networks. Hobbies/Interests: Playing with my kids and playing tennis. Chemistry is fun because there is a chance to see what no one has discovered yet, and any results can contribute to expanding the frontiers of knowledge. I lose my track of time when thinking about the next experiments after getting unexpected results. My motto is: “If you are walking through a dark night with a single lantern, don't be afraid of the darkness; just rely on your lantern.” by a Japanese scholar from the Edo era. I reminded myself of this whenever I hit a stumbling block during my research project. If I were not a scientist, I would be a teacher in an elementary/junior high school and encourage children to be scientists. In three words, how would you describe your research? “Merging synthetic/enzymatic catalysts.” Artificial metalloenzymes (ArMs), which can be constructed by incorporating a synthetic metal complex into a protein matrix, are my main research interests. Thus, my research includes (1) development of synthetic catalysts, (2) protein engineering, and (3) designing catalysis systems composed of natural/artificial enzymes. Is your current research mainly curiosity driven (fundamental) or rather applied? Thus far, almost all of my research has been initiated with applied purposes in mind. However, I always became more interested in the difficulties and unexpected findings that come to light during these projects. Eventually, they end up becoming curiosity-driven projects. What are the main challenges for the future in the broad area of your research? Numerous stoichiometric chemical transformations, such as the detection of biomolecules by fluorescent probes, have been developed in the chemical biology field. In contrast, metal-complex-catalyzing chemical transformations in the cellular environment are still at the early stages of development. This will provide alternative strategies for creating products with new types of medicinal properties. My 3 top papers: 1“An NAD(P)H-Dependent Artificial Transfer Hydrogenase for Multienzymatic Cascades”: J. Am. Chem. Soc. 2016, 138, 5781–5784. We have identified an Ir complex that can utilize NADPH as a hydride source for transfer hydrogenation of imines. Upon incorporation of this Ir complex into streptavidin, the resulting ArM can be coupled with an enzymatic in situ regeneration system of NADPH. This ArM was further integrated into a multi-enzymatic cascade to afford enantiopure amines. Google Scholar 2“Cross-Regulation of an Artificial Metalloenzyme”: Angew. Chem. Int. Ed. 2017, 56, 10156–10160. Biochemical reactions in a living system are tightly cross-regulated by enzymes to maintain homeostasis. In a biomimetic spirit, we have designed a multi-enzymatic reaction network that allows programming the temporal activation of the ArM. Google Scholar 3“A Cell-penetrating Artificial Metalloenzyme Regulates a Gene Switch in a Designer Mammalian Cell”: Nat. Commun. 2018, 9, 1943. Implementing unnatural reactions catalyzed by synthetic catalysts in a cellular environment is challenging owing to the vast number of inactivating molecules. We have developed a cell-penetrating ArM and demonstrated that an intracellular artificial/natural enzymatic cascade upregulates the designed gene switch. Google Scholar Volume12, Issue18September 17, 2020Pages 4501-4501 This article also appears in:Young Researchers Series ReferencesRelatedInformation

Phyllosilicate‐derived Nickel‐cobalt Bimetallic Nanoparticles for the Catalytic Hydrogenation of Imines, Oximes and N‐heteroarenes

AbstractThe development of cost‐effective, noble metal‐free catalytic systems for the hydrogenation of unsaturated aliphatic, aromatic, and heterocyclic compounds is fundamental for future valorization of general feedstock. With this aim, we report here the preparation of highly dispersed bimetallic Ni/Co nanoparticles (NPs), by a one‐pot deposition‐precipitation of Ni and Co phases onto mesoporous SBA‐15 silica. By adjusting the chemical composition in the starting mixture, three supported catalysts with different Ni to Co weight ratios were obtained, which were further subjected to treatments under reducing conditions at high temperatures. Characterization of the resulting solids evidenced a homogenous distribution of Ni and Co elements forming the NPs, the best results being obtained for Ni/Co‐2 : 2 samples, for which 50 wt.% Ni–50 wt.% Co NPs are found located on the surface of the residual phyllosilicate. Ni/Co‐2 : 2, presenting the best performances for the hydrogenation of 2‐methyl‐quinoline, was further evaluated in the catalytic hydrogenation of selected imines, oximes and N‐heteroarenes. Due to the high dispersion of bimetallic Ni−Co NPs, excellent properties (activity and selectivity) in the conversion of the selected substrates are reported.

Metal–Ligand Cooperation Facilitates Bond Activation and Catalytic Hydrogenation with Zinc Pincer Complexes

A series of PNP zinc pincer complexes capable of bond activation via aromatization/dearomatization metal–ligand cooperation (MLC) were prepared and characterized. Reversible heterolytic N–H and H–H bond activation by MLC is shown, in which hemilability of the phosphorus linkers plays a key role. Utilizing this zinc pincer system, base-free catalytic hydrogenation of imines and ketones is demonstrated. A detailed mechanistic study supported by computation implicates the key role of MLC in facilitating effective catalysis. This approach offers a new strategy for (de)hydrogenation and other catalytic transformations mediated by zinc and other main group metals.

Cu‐Al mixed oxide derived from layered double hydroxide as an efficient catalyst for continuous‐flow reductive amination of aromatic aldehydes

AbstractBACKGROUNDSecondary amines are important intermediates in the manufacture of pharmaceuticals and other valuable chemicals. Hence, there is a continuing interest in cost‐effective and environmentally friendly methods for producing these compounds. Reductive amination of aldehydes or ketones with primary amines over heterogeneous metal catalysts is an attractive approach due to the use of inexpensive and environmentally benign molecular hydrogen as a reducing agent.RESULTSVarious secondary amines were obtained by two‐step reductive amination of benzaldehyde derivatives and furfural with primary amines. The condensation of aromatic aldehydes with amines at room temperature in low water methanol gives imines, which are then hydrogenated in a flow reactor over CuAlOx catalyst derived from layered double hydroxide. This process does not require isolation and purification of intermediate imines and can be utilized to obtain several secondary amines in good to excellent yield. The time‐dependent study showed that CuAlOx catalyst demonstrates excellent stability in imine hydrogenation.CONCLUSIONAn environmentally friendly procedure has been developed for the synthesis of secondary amines through a reductive amination of aromatic aldehydes with primary amines over Cu‐based catalyst. This procedure presents a novel way for the sustainable production of secondary amines. © 2020 Society of Chemical Industry

2-[(1E)-[(Z)-2-({[(1Z)-[(E)-2-[(2-Hydroxyphenyl)methylidene]hydrazin-1-ylidene]({[(4-methylphenyl)methyl]sulfanyl})methyl]disulfanyl}({[(4-methylphenyl)methyl]sulfanyl})methylidene)hydrazin-1-ylidene]methyl]phenol: crystal structure, Hirshfeld surface analysis and computational study

The complete mol-ecule of the title hydrazine carbodi-thio-ate derivative, C32H30N4O2S4, is generated by a crystallographic twofold axis that bis-ects the di-sulfide bond. The mol-ecule is twisted about this bond with the C-S-S-C torsion angle of 90.70 (8)° indicating an orthogonal relationship between the symmetry-related halves of the mol-ecule. The conformation about the imine bond [1.282 (2) Å] is E and there is limited delocalization of π-electron density over the CN2C residue as there is a twist about the N-N bond [C-N-N-C torsion angle = -166.57 (15)°]. An intra-molecular hydroxyl-O-H⋯N(imine) hydrogen bond closes an S(6) loop. In the crystal, methyl-ene-C-H⋯π(tol-yl) contacts assemble mol-ecules into a supra-molecular layer propagating in the ab plane: the layers stack without directional inter-actions between them. The analysis of the calculated Hirshfeld surfaces confirm the importance of H⋯H contacts, which contribute 46.7% of all contacts followed by H⋯C/C⋯H contacts [25.5%] reflecting, in part, the C-H⋯π(tol-yl) contacts. The calculation of the inter-action energies confirm the importance of the dispersion term and the influence of the stabilizing H⋯H contacts in the inter-layer region.

Synthesis of a hybrid Pd0/Pd-carbide/carbon catalyst material with high selectivity for hydrogenation reactions

We present a highly selective and active Pd carbon catalyst prepared by an easy hydrothermal synthesis method. This synthetic procedure allows the stabilization under mild conditions of interstitial carbon atoms on the surface of a Pd0 carbon catalyst. The so formed Pd carbide phase appears on the upper surface layers of the Pd carbon catalyst, as demonstrated by X-ray photoelectron depth profile analysis using variable synchrotron X-ray energies. The presence of carbon in the palladium carbide species modifies the electronic state of surface Pd atoms, resulting in more electron positive Pd species (Pdδ+). This influences the adsorption of reactants and reaction intermediates during the hydrogenation of alkynes, dienes and imines, resulting in high selectivities at practically 100% conversion.

Chiral metal-organic frameworks with tunable catalytic selectivity in asymmetric transfer hydrogenation reactions

Metal-organic frameworks (MOFs) have achieved great success in the field of heterogeneous catalysis, however, it’s still challenging to design MOF catalysts with enhanced selectivity. Here, we demonstrated a combination strategy of metal design and ligand design on the enantioselectivity—that is the enantioselectivities of chiral MOF (CMOF) catalysts could be significantly enhanced by the rational choice of metal ions with higher electronegativities and introducing sterically demanding groups into the ligands. Four isostructural Ca-, Sr- and Zn-based CMOFs were prepared from enantiopure phosphono-carboxylate ligands of 1,1′-biphenol that are functionalized with 2,4,6-trimethyl- and 2,4,6-trifluoro-phenyl groups at the 3,3’-position. The uniformly distributed metal phosphonates along the channels could act as Lewis acids and catalyze the asymmetric transfer hydrogenation of heteroaromatic imines (benzoxazines and quinolines). Particularly, the Ca-based MOF 1 with 2,4,6-trimethyl groups at the substituents exhibited enhanced catalytic performance, affording the highest enantioselectivity (up to 97%). It is also the first report of the heterogeneous catalyst with chiral non-noble metal phosphonate active sites for asymmetric transfer hydrogenation reactions with Hantzsch ester as the hydrogen source. The catalyst design strategy demonstrated here is expected to develop new types of chiral materials for asymmetric catalysis and other chiral applications.

Asymmetric Induction with a Chiral Amine Catalyzed by a Ru-PNP Pincer Complex: Insight from Theoretical Investigation.

In this paper, the mechanism of asymmetric amination of a racemic alcohol with Ellman's sulfinamide and the origin of diastereoselectivity catalyzed by a Ru-PNP pincer complex were studied using density functional theory (DFT). The mechanism involves dehydrogenation of the racemic alcohol, C-N coupling, and hydrogen transfer from the catalyst to the in situ formed imine. The calculated results indicate that both the alcohol dehydrogenation and imine hydrogenation are stepwise. The hydride transfer from a Ru hydride complex to the imine is shown to be the chirality-determining step in the whole catalytic cycle. It was found that the diastereoselectivity mainly stems from the hydrogen bonding interactions between the oxygen atom of the sulfinyl moiety and the hydrogen atom of the NH group of the ligand.

4-[(1E)-({[(Benzyl-sulfan-yl)methane-thio-yl]amino}-imino)-meth-yl]benzene-1,3-diol chloro-form hemisolvate: crystal structure, Hirshfeld surface analysis and computational study.

The title hydrazine carbodi-thio-ate chloro-form hemisolvate, 2C15H14N2O2S2·CHCl3, comprises two independent hydrazine carbodi-thio-ate mol-ecules, A and B, and a chloro-form mol-ecule; the latter is statistically disordered about its mol-ecular threefold axis. The common features of the organic mol-ecules include an almost planar, central CN2S2 chromophore [r.m.s. deviation = 0.0203 Å (A) and 0.0080 Å (B)], an E configuration about the imine bond and an intra-molecular hydroxyl-O-H⋯N(imine) hydrogen bond. The major conformational difference between the mol-ecules is seen in the relative dispositions of the phenyl rings as indicated by the values of the dihedral angles between the central plane and phenyl ring of 71.21 (6)° (A) and 54.73 (7)° (B). Finally, a difference is seen in the disposition of the outer hydroxyl-H atoms, having opposite relative orientations. In the calculated gas-phase structure, the entire mol-ecule is planar with the exception of the perpendicular phenyl ring. In the mol-ecular packing, the A and B mol-ecules assemble into a two-mol-ecule aggregate via N-H⋯S hydrogen bonds and eight-membered {⋯HNCS}2 synthons. The dimeric assemblies are connected into supra-molecular chains via hydroxyl-O-H⋯O(hydrox-yl) hydrogen bonds and these are linked into a double-chain through hy-droxy-O-H⋯π(phen-yl) inter-actions. The double-chains are connected into a three-dimensional architecture through phenyl-C-H⋯O(hydrox-yl) and phenyl-C-H⋯π(phen-yl) inter-actions. The overall assembly defines columns along the a-axis direction in which reside the chloro-form mol-ecules, which are stabilized by chloro-form-methine-C-H⋯S(thione) and phenyl-C-H⋯Cl contacts. The analysis of the calculated Hirshfeld surfaces, non-covalent inter-action plots and inter-action energies confirm the importance of the above-mentioned inter-actions, but also of cooperative, non-standard inter-actions such as π(benzene)⋯π(hydrogen-bond-mediated-ring) contacts.

Crystal structures of two dis-symmetric di-Schiff base compounds: 2-({(E)-2-[(E)-2,6-di-chloro-benzyl-idene]hydrazin-1-yl-idene}meth-yl)-6-meth-oxy-phenol and 4-bromo-2-({(E)-2-[(E)-2,6-di-chloro-benzyl-idene]hydrazin-1-yl-idene}meth-yl)phenol.

Each of the title dis-symmetric di-Schiff base compounds, C15H12Cl2N2O2 (I) and C14H9BrCl2N2O (II), features a central azo-N-N bond connecting two imine groups, each with an E-configuration. One imine bond in each mol-ecule connects to a 2,6-di-chloro-benzene substituent while the other links a 2-hydroxyl-3-meth-oxy-substituted benzene ring in (I) or a 2-hydroxyl-4-bromo benzene ring in (II). Each mol-ecule features an intra-molecular hydroxyl-O-H⋯N(imine) hydrogen bond. The C-N-N-C torsion angles of -151.0 (3)° for (I) and 177.8 (6)° (II) indicates a significant twist in the former. The common feature of the mol-ecular packing is the formation of supra-molecular chains. In (I), the linear chains are aligned along the a-axis direction and the mol-ecules are linked by meth-oxy-C-H⋯O(meth-oxy) and chloro-benzene-C-Cl⋯π(chlorobenzene) inter-actions. The chain in (II) is also aligned along the a axis but, has a zigzag topology and is sustained by Br⋯O [3.132 (4) Å] secondary bonding inter-actions. In each crystal, the chains pack without directional inter-actions between them. The non-covalent inter-actions are delineated in the study of the calculated Hirshfeld surfaces. Dispersion forces make the most significant contributions to the identified inter-molecular inter-actions in each of (I) and (II).

Alkaline Earth Metal Aluminates as Catalysts for Imine Hydrogenation

Alkaline earth (Ae) metal complexes with the alanate anion AlH4– have been prepared by salt metathesis between NaAlH4 and AeCl2 in THF and could be isolated as Mg(AlH4)2·(THF)4, Ca(AlH4)2·(THF)4, a...

Reduction hydrogenation of imines by in situ generated rhodium NHC complexes

In this paper we examined the catalytic activity of in situ prepared bidentate azolium salt/[RhCl(COD)]2 catalyst system in the transfer hydrogenation of imines with i-propanol to the corresponding amine. The first in situ transfer hydrogenation of imines to amines is described using [RhCl(COD)]2 with bidentate azolium ligands. New bidentate azolium salts (1a-c, 2a-c) as NHC precursors have been synthesized and characterized. The in situ prepared three-component bidentate azolium salts (LHX)/[RhCl(COD)]2 and t-BuOK catalyzes quantitatively the transfer hydrogenation of imines under mild reaction conditions in i-propanol. The results show that bidentate benzimidazolium salts were observed to be more active in reducing imines. Moreover, the method is simple and effective against various imines.

Amino hydroxyapatite/chitosan hybrids reticulated with glutaraldehyde at different pH values and their use for diclofenac removal

Diclofenac sodium (DS) is an emergent pollutant, and among the methods investigated for its removal, adsorption is the most widely utilized technique. Hydroxyapatite and chitosan are biomaterials often used for adsorption. However, both biomaterials are limited due to their low chemical stability in an acidic medium; furthermore, pure hydroxyapatite interacts poorly with diclofenac. In this work, hydroxyapatite was organofunctionalized with 3-aminopropyltrimethoxysilane and further used to obtain amino hydroxyapatite /chitosan hybrids by crosslinking with glutaraldehyde at pH 3, 4, 5, and 6. X-ray diffraction patterns indicated the preservation of the hydroxyapatite phase under all pH conditions. Based on the control reaction of the amino hydroxyapatite with glutaraldehyde and its further reduction in sodium borohydride, the formation of CN moieties was highlighted as the main interaction mechanism between the aldehyde and amino groups. Therefore, crosslinking with glutaraldehyde was evaluated by infrared, Raman spectroscopy, and 13C NMR techniques; the results suggested contributions of imine formation and hydrogen bonding. The hybrid obtained at pH 3 exhibited an enhanced adsorption capacity of 125 mg g−1 at 15 min. The synergy between amino hydroxyapatite and chitosan crosslinked by glutaraldehyde was demonstrated.

Replacement of Pd nanoparticles: Hydrogenation promoted by frustrated Lewis acid-base pairs in carbon quantum dots

Due to the scarcity of the noble metals and their high price, the use of carbon-based materials to replace the noble metal catalysts has attracted extensive current research interest. Herein, we reported that carbon quantum dots (CQDs) can be used to replace Pd nanoparticles in hydrogenation reactions due to the presence of the frustrated Lewis acid-base pairs (FLPs), as demonstrated experimentally and supported theoretically. By coupling the hydrogenation of imines over CQDs with ZnIn2S4-based photocatalytic dehydrogenation of alcohols, N-alkylation of amines with alcohols have been successfully realized over CQDs/ZnIn2S4, with performance comparable to that observed over Pd/ZnIn2S4 nanocomposite, demonstrating the possibility of using CQDs to substitute Pd nanoparticles in hydrogenation of imines. This work shows enormous potential of employing the CQDs in chemical reactions to reduce the current dependence on noble metal-based catalysts.

Simple manganese carbonyl catalyzed hydrogenation of quinolines and imines

Manganese-catalyzed hydrogenation of unsaturated molecules has made tremendous progresses recently benefiting from non-innocent pincer or bidentate ligands for manganese. Herein, we describe the hydrogenation of quinolines and imines catalyzed by simple manganese carbonyls, Mn2(CO)10 or MnBr(CO)5, thus eliminating the prerequisite pincer-type or bidentate ligands.

Machine learning for asymmetric catalysis

Organic Chemistry Catalysts can introduce asymmetry in the outcome of chemical reactions, favoring one mirror-image product over another. Many of the most effective catalysts for this application were optimized through trial and error, but more recently, parameterization and systematic analysis have played an increasing role. Singh et al. now showcase the predictive power of machine learning applied to the ligands used for asymmetric hydrogenation. A random forest algorithm trained on several different families of chiral binaphthyl phosphorus compounds predicted selectivity in hydrogenation of alkenes and imines with a root-mean-square error of just over 8%. Proc. Natl. Acad. Sci. U.S.A. 117 , 1339 (2020).

Cross-Linked Cyclodextrins Bimetallic Nanocatalysts: Applications in Microwave-Assisted Reductive Aminations.

The optimization of sustainable protocols for reductive amination has been a lingering challenge in green synthesis. In this context, a comparative study of different metal-loaded cross-linked cyclodextrins (CDs) were examined for the microwave (MW)-assisted reductive amination of aldehydes and ketones using either H2 or formic acid as a hydrogen source. The Pd/Cu heterogeneous nanocatalyst based on Pd (II) and Cu (I) salts embedded in a β-CD network was the most efficient in terms of yield and selectivity attained. In addition, the polymeric cross-linking avoided metal leaching, thus enhancing the process sustainability; good yields were realized using benzylamine under H2. These interesting findings were then applied to the MW-assisted one-pot synthesis of secondary amines via a tandem reductive amination of benzaldehyde with nitroaromatics under H2 pressure. The formation of a CuxPdy alloy under reaction conditions was discerned, and a synergic effect due to the cooperation between Cu and Pd has been hypothesized. During the reaction, the system worked as a bifunctional nanocatalyst wherein the Pd sites facilitate the reduction of nitro compounds, while the Cu species promote the subsequent imine hydrogenation affording structurally diverse secondary amines with high yields.

Transfer Hydrogenation of Ketones and Imines with Methanol under Base-Free Conditions Catalyzed by an Anionic Metal-Ligand Bifunctional Iridium Catalyst.

An anionic iridium complex [Cp*Ir(2,2'-bpyO)(OH)][Na] was found to be a general and highly efficient catalyst for transfer hydrogenation of ketones and imines with methanol under base-free conditions. Readily reducible or labile substituents, such as nitro, cyano, and ester groups, were tolerated under present reaction conditions. Notably, this study exhibits the unique potential of anionic metal-ligand bifunctional iridium catalysts for transfer hydrogenation with methanol as a hydrogen source.

A unified machine-learning protocol for asymmetric catalysis as a proof of concept demonstration using asymmetric hydrogenation

Design of asymmetric catalysts generally involves time- and resource-intensive heuristic endeavors. In view of the steady increase in interest toward efficient catalytic asymmetric reactions and the rapid growth in the field of machine learning (ML) in recent years, we envisaged dovetailing these two important domains. We selected a set of quantum chemically derived molecular descriptors from five different asymmetric binaphthyl-derived catalyst families with the propensity to impact the enantioselectivity of asymmetric hydrogenation of alkenes and imines. The predictive power of the random forest (RF) built using the molecular parameters of a set of 368 substrate-catalyst combinations is found to be impressive, with a root-mean-square error (rmse) in the predicted enantiomeric excess (%ee) of about 8.4 ± 1.8 compared to the experimentally known values. The accuracy of RF is found to be superior to other ML methods such as convolutional neural network, decision tree, and eXtreme gradient boosting as well as stepwise linear regression. The proposed method is expected to provide a leap forward in the design of catalysts for asymmetric transformations.

Alcohol amination over titania-supported ruthenium nanoparticles

Smaller ruthenium nanoparticles over titania exhibit higher selectivity to primary amines because of suppressing imine hydrogenation.