Dehydrogenation Of Amines Research Articles

Osmium Catalysts for Acceptorless and Base-Free Dehydrogenation of Alcohols and Amines: Unusual Coordination Modes of a BPI Anion

A novel type of catalyst precursors for the dehydrogenation of hydrogen carriers based on organic liquids has been discovered. Complexes OsH6(PiPr3)2 (1) and OsH(OH)(CO)(PiPr3)2 (2) react with 1,3-bis(6′-methyl-2′-pyridylimino)isoindoline (HBMePI) to give OsH3{κ2-Npy,Nimine-(BMePI)}(PiPr3)2 (3) and OsH{κ2-Npy,Nimine-(BMePI)}(CO)(PiPr3)2 (4). The unprecedented κ2-Npy,Nimine coordination mode of BMePI is thermodynamically preferred with Os(IV) and Os(II) metal fragments and allows for preparation of BMePI-based dinuclear metal cations. Treatment of OsH2Cl2(PiPr3)2 (5) with 0.5 equiv of HBMePI in the presence of KOtBu affords the chloride salt of the bis(osmium(IV)) dinuclear cation [{OsH3(PiPr3)2}2{μ-(κ2-Npy,Nimine)2-BMePI}]+ (6). Related homoleptic bis(osmium(II)) complexes have been also synthesized. Complex 4 reacts with the bis(solvento) [OsH(CO){κ1-O-[OCMe2]2}(PiPr3)2]BF4 to give [{OsH(CO)(PiPr3)2}2{μ-(κ2-Npy,Nimine)2-BMePI}]BF4 (7), whereas the addition of 0.5 equiv of HBMePI to {OsCl(η6-C6H6)}2(μ–Cl)...

Preparation of polydimethylsiloxane with amino end group via Pd-catalyzed dehydrogenative coupling of terminal hydrosilyl unit and amine

Ring-opening polymerization of hexamethylcyclotrisiloxane (D3) with organolithium reagents (R1Li) followed by quenching of the resulting anions with chlorodimethylsilane yielded the corresponding polysiloxanes with R1 and SiMe2H groups at each end. The hydrosilyl end groups readily underwent palladium-catalyzed dehydrogenative amination reactions with secondary amines (R22NH) to produce polysiloxanes with amino end groups, R1(SiMe2O)nSiMe2NR22. The aminopolysiloxanes were applied as hydrophobic modifiers of glass surface and treatment of glass plates with THF solutions of the aminopolysiloxanes increased the water contact angles of the glass surface from 5° to 22°–65°, depending on the aminopolysiloxane structures and the reaction conditions.

Aerobic Oxidative Dehydrogenation of Amines Catalyzed by a Recoverable Ruthenium Catalyst under Mild Reaction Conditions

AbstractA highly active catalyst based on perruthenate ions supported inside the channels of periodic mesoporous organosilica with a bridged imidazolium ionic liquid framework (Ru@PMO‐IL) was developed. The material was found to be an efficient, durable, and recoverable catalyst for the oxidative dehydrogenation of various types of amines such as benzylic, aliphatic, and cyclic aliphatic amines under mild reaction conditions. The products were obtained in excellent yields with excellent selectivities.

Where does Au coordinate to N-(2-pyridiyl)benzotriazole: gold-catalyzed chemoselective dehydrogenation and borrowing hydrogen reactions

Pyridyltriazole gold(i) complexes proved to be an efficient precatalyst for the most challenging gold-catalyzed borrowing hydrogen reaction and dehydrogenation of alcohols and amines.

Tunable Cu(i)-catalyzed site-selective dehydrogenative amination of β,γ-unsaturated hydrazones for divergent synthesis of pyrazol-4-ones and 1,6-dihydropyradazines

A new tunable Cu(i)-catalyzed site-selective dehydrogenative amination of β,γ-unsaturated hydrazones has been established using readily accessible dioxygen as a green oxidant.

FeCl3–Catalyzed Cascade Reactions of Cyclic Amines with 2‐Oxo‐2‐arylacetic Acids toward Furan‐2(5H)‐one Fused N,O‐Bicyclic Compounds

AbstractA novel and efficient synthesis of furan‐2(5H)‐one fused N,O‐containing bicyclic compounds via the cascade reactions of N‐aryl substituted cyclic amines with 2‐oxo‐2‐arylacetic acids is presented. Mechanistically, the formation of the title compounds is initiated by the in situ formation of a cyclic enamine intermediate via FeCl3/di‐tert‐butyl peroxide (TBP)/oxygen (O2)‐promoted C(sp3)−H dehydrogenation of saturated cyclic amine. Nucleophilic addition of the cyclic enamine intermediate onto 2‐oxo‐2‐arylacetic acid followed by cyclization and dehydration gives the bicyclic heterocycle products. This intermolecular oxidative annulation constitutes an extension of tertiary amine‐based Mannich‐type β‐functionalization leading to a series of N,O‐bycyclic compounds in good yields with ease.magnified image

Copper‐Catalyzed Aerobic Annulation of Hydrazones: Direct Access to Cinnolines

AbstractA novel method was developed for the construction of biologically active poly‐substituted cinnolines from easily accessible hydrazones in good to excellent yields. A simple copper catalyst could efficiently promote C−N bond formation through selective C−H functionalization and dehydrogenative amination. Furthermore, the inert C−Heteroatom (O/F/N) bonds are susceptible to cleavage in high selectivity in the newly developed aerobic annulation, in preference to the alternative C−H bond, which is left intact.magnified image

Ruthenium‐Catalyzed Oxidative Formal Aza‐Diels–Alder Reaction: Enantioselective Synthesis of Benzo[a]quinolizine‐2‐ones

AbstractA method for the preparation of thermodynamic (4R,11bS)‐benzo[a]quinolizine‐2‐one derivatives in good enantio‐ and diastereoselectivity by a one‐pot oxidative formal aza‐Diels–Alder reaction of 1,2,3,4‐tetrahydroisoquinolines and α,β‐unsaturated ketones is described. The reaction proceeds via tandem ruthenium‐catalyzed amine dehydrogenation using tert‐butyl hydroperoxide (TBHP) as the oxidant and a chiral thiourea‐catalyzed formal aza‐[4+2] cycloaddition, providing a step‐economical strategy for the synthesis of these valuable heterocyclic products.magnified image

Osmium Hydride Acetylacetonate Complexes and Their Application in Acceptorless Dehydrogenative Coupling of Alcohols and Amines and for the Dehydrogenation of Cyclic Amines

The preparation of new osmium hydride complexes, starting from OsH6(PiPr3)2 (1) and OsH2Cl2(PiPr3)2 (2), and their catalytic activity in acceptorless dehydrogenative coupling of alcohols and amines and in dehydrogenation of cyclic amines are reported. Complex 1 reacts with acetylacetone (Hacac) to give the classical trihydride OsH3(acac)(PiPr3)2 (3). The protonation of 3 with triflic acid (HOTf) produces the release of H2 and the formation of the unsaturated osmium(IV) dihydride [OsH2(acac)(PiPr3)2]OTf (4), which is also prepared by starting from 2 via the intermediate OsH2Cl(acac)(PiPr3)2 (5). Treatment of an acetylacetone solution of 5 with KOH affords Os(acac)2(PiPr3)2 (6). In the presence of 5 mol % of KOH, complexes 3–6 promote the coupling of benzyl alcohol and aniline to give N-benzylideneaniline and H2. Under the same conditions, complex 3 catalyzes a wide range of analogous couplings to afford a variety of imines, including aliphatic imines, with yields between 90 and 40% after 1–48 h. Complex 3 ...

Triazolylidene-Iridium Complexes with a Pendant Pyridyl Group for Cooperative Metal-Ligand Induced Catalytic Dehydrogenation of Amines.

Two iridium(III) complexes containing a C,N-bidentate pyridyl-triazolylidene ligand were prepared that are structurally very similar but differ in their pendant substituent. Whereas complex 1 contains a non-coordinating pyridyl unit, complex 2 has a phenyl group on the triazolylidene substituent. The presence of the basic pyridyl unit has distinct effects on the catalytic activity of the complex in the oxidative dehydrogenation of benzylic amines, inducing generally higher rates, higher selectivity towards formation of imines versus secondary amines, and notable quantities of tertiary amines when compared to the phenyl-functionalized analogue. The role of the pyridyl functionality has been elucidated from a set of stoichiometric experiments, which demonstrate hydrogen bonding between the pendant pyridyl unit and the amine protons of the substrate. Such Npyr ⋅⋅⋅H-N interactions are demonstrated by X-ray diffraction analysis, 1 H NMR, and IR spectroscopy, and suggest a pathway of substrate bond-activation that involves concerted substrate binding through the Lewis acidic iridium center and the Lewis basic pyridyl site appended to the triazolylidene ligand, in agreement with ligand-metal cooperative substrate activation.

Unified Synthesis of 1,2-Oxy-aminoarenes via a Bio-inspired Phenol-Amine Coupling

Summary 1,2-Aminophenols and their related nitrogen-containing heterocycles are ubiquitous in medicine, agriculture, and materials science. Here, we describe a bio-inspired and unified approach for their synthesis through a direct, catalytic aerobic coupling of phenols and amines. Key to the formation of the aromatic C–N bond is a facile condensation between the amine and an ortho -quinone, which triggers redox isomerization to an ortho -iminophenol before a series of downstream events. We discuss the factors that govern regioselectivity during aerobic ortho -oxygenation of the phenol and condensation of the amine, and we demonstrate synthetic utility by preparing a structurally diverse family of immunosuppressive heterocycles and the indole alkaloid cephalandole A. Our conditions involve a wide range of simple, un-activated substrates, occur at room temperature with an earth-abundant copper-catalyst and a commercially available diamine ligand, and produce water as the only stoichiometric by-product.

Nature Inspires an Aerobic Coupling of Phenol and Amine

In this issue of Chem , Lumb and colleagues report on an effective and simple catalytic system of copper and diamine ligands for the bio-inspired and unified synthesis of 1,2-aminophenols through direct aerobic phenol-amine coupling. Using this method, they prepared a structurally diverse family of 1,2-aminophenols and their derived heterocycles, including immunosuppressive benzoxazoles and the indole alkaloid cephalandole A.

Versatile routes for synthesis of diarylamines through acceptorless dehydrogenative aromatization catalysis over supported gold-palladium bimetallic nanoparticles.

Diarylamines are an important class of widely utilized chemicals, and development of diverse procedures for their synthesis is of great importance. Herein, we have successfully developed novel versatile catalytic procedures for the synthesis of diarylamines through acceptorless dehydrogenative aromatization. In the presence of a gold-palladium alloy nanoparticle catalyst (Au-Pd/TiO2), various symmetrically substituted diarylamines could be synthesized starting from cyclohexylamines. The observed catalysis of Au-Pd/TiO2 was heterogeneous in nature and Au-Pd/TiO2 could be reused several times without severe loss of catalytic performance. This transformation needs no oxidants and generates molecular hydrogen (three equivalents with respect to cyclohexylamines) and ammonia as the side products. These features highlight the environmentally benign nature of the present transformation. Furthermore, in the presence of Au-Pd/TiO2, various kinds of structurally diverse unsymmetrically substituted diarylamines could successfully be synthesized starting from various combinations of substrates such as (i) anilines and cyclohexanones, (ii) cyclohexylamines and cyclohexanones, and (iii) nitrobenzenes and cyclohexanols. The role of the catalyst and the reaction pathways were investigated in detail for the transformation of cyclohexylamines. The catalytic performance was strongly influenced by the nature of the catalyst. In the presence of a supported gold nanoparticle catalyst (Au/TiO2), the desired diarylamines were hardly produced. Although a supported palladium nanoparticle catalyst (Pd/TiO2) gave the desired diarylamines, the catalytic activity was inferior to that of Au-Pd/TiO2. Moreover, the activity of Au-Pd/TiO2 was superior to that of a physical mixture of Au/TiO2 and Pd/TiO2. The present Au-Pd/TiO2-catalyzed transformation of cyclohexylamines proceeds through complex pathways comprising amine dehydrogenation, imine disproportionation, and condensation reactions. The amine dehydrogenation and imine disproportionation reactions are effectively promoted by palladium (not by gold), and the intrinsic catalytic performance of palladium is significantly improved by alloying with gold. One possible explanation of the alloying effect is the formation of electron-poor palladium species that can effectively promote the β-H elimination step in the rate-limiting amine dehydrogenation.

Dehydrogenation of cyclic amines by a coordinatively unsaturated Cp*Ir(iii) phosphoramidate complex.

The reaction of a Cp*Ir(iii) phosphoramidate complex with secondary amines gives amine, imine-bound Cp*Ir(iii) hydride complexes resulting from amine dehydrogenation. These well-characterized species could serve as models of relevant intermediates that have been proposed in catalytic amine dehydrogenation using related N,O-chelated Cp*Ir(iii) pyridonate complexes.

Tryptophan lyase (NosL): mechanistic insights into amine dehydrogenation and carboxyl fragment migration by QM/MM calculations

QM/MM calculations suggest two feasible pathways for the breaking of the C–C bond of the substrate. The breaking of the Cα–Cβ bond leads to the final product, whereas the cleavage of the Cα–C bond will terminate in the EPR-trapped radical intermediate.

Development of a metal-free amine oxidation method utilizing DEAD chemistry

Development of a metal-free methodology for the efficient and general dehydrogenation of amines, accomplished by employing azodicarboxylate as oxidizing agents.

Dehydrogenative Amination of Phenols with Phenothiazines

Dehydrogenative Amination of Phenols with Phenothiazines

Catalytic Hydrogen Production by Ruthenium Complexes from the Conversion of Primary Amines to Nitriles: Potential Application as a Liquid Organic Hydrogen Carrier.

The potential application of the primary amine/nitrile pair as a liquid organic hydrogen carrier (LOHC) has been evaluated. Ruthenium complexes of formula [(p-cym)Ru(NHC)Cl2 ] (NHC=N-heterocyclic carbene) catalyze the acceptorless dehydrogenation of primary amines to nitriles with the formation of molecular hydrogen. Notably, the reaction proceeds without any external additive, under air, and under mild reaction conditions. The catalytic properties of a ruthenium complex supported on the surface of graphene have been explored for reutilization purposes. The ruthenium-supported catalyst is active for at least 10 runs without any apparent loss of activity. The results obtained in terms of catalytic activity, stability, and recyclability are encouraging for the potential application of the amine/nitrile pair as a LOHC. The main challenge in the dehydrogenation of benzylamines is the selectivity control, such as avoiding the formation of imine byproducts due to transamination reactions. Herein, selectivity has been achieved by using long-chain primary amines such as dodecylamine. Mechanistic studies have been performed to rationalize the key factors involved in the activity and selectivity of the catalysts in the dehydrogenation of amines. The experimental results suggest that the catalyst resting state contains a coordinated amine.

Direct and Efficient Dehydrogenation of Tetrahydroquinolines and Primary Amines Using Corona Discharge Generated on Ambient Hydrophobic Paper Substrate

The exposure of an aqueous-based liquid drop containing amines and graphite particles to plasma generated by a corona discharge results in heterogeneous aerobic dehydrogenation reactions. This green oxidation reaction occurring in ambient air afforded the corresponding quinolines and nitriles from tetrahydroquinolines and primary amines, respectively, at >96% yields in less than 2min of reaction time. The accelerated dehydrogenation reactions occurred on the surface of a low energy hydrophobic paper, which served both as container for holding the reacting liquid drop and as a medium for achieving paper spray ionization of reaction products for subsequent characterization by ambient mass spectrometry. Control experiments indicate superoxide anions (O2•-) are the main reactive species; the presence of graphite particles introduced heterogeneous surface effects, and enabled the efficient sampling of the plasma into the grounded analyte droplet solution. Graphical Abstract ᅟ.

Mild, Periodate-Mediated, Dehydrogenative C-N Bond Formation with Phenothiazines and Phenols.

The dehydrogenative amination of phenols with phenothiazines was achieved in transition-metal-free conditions, utilizing cheap sodium periodate as oxidant, at low temperature. A significantly larger scope of phenol substrates was tolerated compared to previous methods.