- Vanadium-and chromium-catalyzed dehydrogenative synthesis of imines from alcohols and amines
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Vanadium(IV) tetraphenylporphyrin dichloride and chromium(III) tetraphenylporphyrin chloride have been developed as catalysts for the acceptorless dehydrogenation of alcohols. The catalysts have been applied to the direct synthesis of imines in overall good yields from a variety of alcohols and amines. The transformations are proposed to proceed by metal?ligand bifunctional pathways with an outer-sphere transfer of two hydrogen atoms from the alcohol to the metal porphyrin complexes. The results show that vanadium and chromium catalysts can also be employed for the dehydrogenation of alcohols with the release of hydrogen gas, and they may represent valuable alternatives to other catalysts based on Earth-abundant metals.
- Madsen, Robert,Miao, Yulong,Samuelsen, Simone V.
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supporting information
p. 1328 - 1335
(2021/05/29)
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- Synthesis, characterization and C-H amination reactivity of nickel iminyl complexes
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Metalation of the deprotonated dipyrrin (AdFL)Li with NiCl2(py)2 afforded the divalent Ni product (AdFL)NiCl(py)2 (1) (AdFL: 1,9-di(1-adamantyl)-5-perfluorophenyldipyrrin; py: pyridine). To generate a reactive synthon on which to explore oxidative group transfer, we used potassium graphite to reduce 1, affording the monovalent Ni synthon (AdFL)Ni(py) (2) and concomitant production of a stoichiometric equivalent of KCl and pyridine. Slow addition of mesityl- or 1-adamantylazide in benzene to 2 afforded the oxidized Ni complexes (AdFL)Ni(NMes) (3) and (AdFL)Ni(NAd) (4), respectively. Both 3 and 4 were characterized by multinuclear NMR, EPR, magnetometry, single-crystal X-ray crystallography, theoretical calculations, and X-ray absorption spectroscopies to provide a detailed electronic structure picture of the nitrenoid adducts. X-ray absorption near edge spectroscopy (XANES) on the Ni reveals higher energy Ni 1s → 3d transitions (3: 8333.2 eV; 4: 8333.4 eV) than NiI or unambiguous NiII analogues. N K-edge X-ray absorption spectroscopy performed on 3 and 4 reveals a common low-energy absorption present only for 3 and 4 (395.4 eV) that was assigned via TDDFT as an N 1s promotion into a predominantly N-localized, singly occupied orbital, akin to metal-supported iminyl complexes reported for iron. On the continuum of imido (i.e., NR2-) to iminyl (i.e., 2NR-) formulations, the complexes are best described as NiII-bound iminyl species given the N K-edge and TDDFT results. Given the open-shell configuration (S = 1/2) of the iminyl adducts, we then examined their propensity to undergo nitrenoid-group transfer to organic substrates. The adamantyl complex 4 readily consumes 1,4-cyclohexadiene (CHD) via H-atom abstraction to afford the amide (AdFL)Ni(NHAd) (5), whereas no reaction was observed upon treatment of the mesityl variant 3 with excess amount of CHD over 3 hours. Toluene can be functionalized by 4 at room temperature, exclusively affording the N-1-adamantyl-benzylidene (6). Slow addition of the organoazide substrate (4-azidobutyl)benzene (7) with 2 exclusively forms 4-phenylbutanenitrile (8) as opposed to an intramolecular cyclized pyrrolidine, resulting from facile β-H elimination outcompeting H-atom abstraction from the benzylic position, followed by rapid H2-elimination from the intermediate Ni hydride ketimide intermediate.
- Dong, Yuyang,Lukens, James T.,Clarke, Ryan M.,Zheng, Shao-Liang,Lancaster, Kyle M.,Betley, Theodore A.
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p. 1260 - 1268
(2020/02/15)
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- Photoredox-catalyzed deaminative alkylation via C-N bond activation of primary amines
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Primary amines are often cheap, naturally occurring, and chemically diverse starting materials. For these reasons, deaminative functionalization of amines has emerged as an important area of research. Recent advances in C-N activation transform simple α-1° and α-2° amines into alkylating reagents via Katritzky pyridinium salts. We report a complementary method that activates sterically encumbered α-3° primary amines through visible light photoredox catalysis. By condensing α-3° primary amines with electron-rich aryl aldehyde, we enable an oxidation and deprotonation event, which generates a key imidoyl radical intermediate. A subsequent β-scission event liberates alkyl radicals for coupling with electron-deficient olefins for the generation of unnatural γ-quaternary amino acids and other valuable synthetic targets.
- Ashley, Melissa A.,Rovis, Tomislav
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supporting information
p. 18310 - 18316
(2020/11/17)
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- Development and mechanistic investigation of the manganese(iii) salen-catalyzed dehydrogenation of alcohols
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The first example of a manganese(iii) catalyst for the acceptorless dehydrogenation of alcohols is presented. N,N′-Bis(salicylidene)-1,2-cyclohexanediaminomanganese(iii) chloride (2) has been shown to catalyze the direct synthesis of imines from a variety of alcohols and amines with the liberation of hydrogen gas. The mechanism has been investigated experimentally with labelled substrates and theoretically with DFT calculations. The results indicate a metal-ligand bifunctional pathway in which both imine groups in the salen ligand are first reduced to form a manganese(iii) amido complex as the catalytically active species. Dehydrogenation of the alcohol then takes place by a stepwise outer-sphere hydrogen transfer generating a manganese(iii) salan hydride from which hydrogen gas is released.
- Samuelsen, Simone V.,Santilli, Carola,Ahlquist, M?rten S. G.,Madsen, Robert
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p. 1150 - 1157
(2019/02/03)
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- Manganese(III) Porphyrin-Catalyzed Dehydrogenation of Alcohols to form Imines, Tertiary Amines and Quinolines
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Manganese(III) porphyrin chloride complexes have been developed for the first time as catalysts for the acceptorless dehydrogenative coupling of alcohols and amines. The reaction has been applied to the direct synthesis of imines, tertiary amines and quinolines where only hydrogen gas and/or water are formed as the by-product(s). The mechanism is believed to involve the formation of a manganese(III) alkoxide complex which degrades into the aldehyde and a manganese(III) hydride species. The latter reacts with the alcohol to form hydrogen gas and thereby regenerates the alkoxide complex.
- Azizi, Kobra,Akrami, Sedigheh,Madsen, Robert
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p. 6439 - 6446
(2019/04/26)
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- In Situ Generated Cobalt Catalyst for the Dehydrogenative Coupling of Alcohols and Amines into Imines
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An in situ formed cobalt catalyst is developed from cobalt(II)bromide, bis[2-(diisopropylphosphino)-4-methylphenyl]amine and zinc metal. The catalyst mediates the acceptorless dehydrogenative coupling of alcohols and amines into imines with the release of hydrogen gas and the transformation is applied to the synthesis of a variety of imines from different alcohols and amines. The mechanism is investigated with labelled substrates and based on the results a cobalt(I) PNP complex is believed to be the catalytically active species which abstracts hydrogen gas from the alcohol through a metal ligand bifunctional pathway.
- Bottaro, Fabrizio,Madsen, Robert
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p. 2707 - 2712
(2019/05/15)
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- Molybdenum-Catalyzed Dehydrogenative Synthesis of Imines from Alcohols and Amines
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A molybdenum N-heterocyclic carbene catalyst has been developed for the synthesis of imines from primary alcohols and amines with the liberation of dihydrogen. The catalyst is generated in situ from molybdenum hexacarbonyl, 1,3-dicyclohexylimidazolium chloride and potassium tert-butoxide and is further stabilized by the phosphine ligand dppe. Imines are formed in moderate to good isolated yields and a variety of alcohols and amines can be employed in the reaction including anilines. The transformation constitutes the first example of a homogeneous molybdenum-catalyzed acceptorless dehydrogenative coupling with alcohols and is believed to proceed by formation of a cis-coordinated molybdenum bis-N-heterocyclic carbene complex, which performs an oxidative addition to the alcohol, β-hydride elimination and reductive elimination of dihydrogen.
- Azizi, Kobra,Madsen, Robert
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p. 3703 - 3708
(2018/07/31)
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- Aerobic Oxidative Homo- and Cross-Coupling of Amines Catalyzed by Phenazine Radical Cations
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Phenazine radical cations (PhRCs) were used for the first time as efficient metal-free catalysts for the oxidative homo- and cross-coupling of a variety of different amines. A series of functional PhRCs were prepared, characterized with X-ray diffraction, and their radical character was investigated with DFT calculations. They were tested as catalysts under neat conditions with low oxygen pressure to prepare homo- and cross-coupled aliphatic and aromatic imines in high yields. Although all synthesized phenazines were catalytically active, the highest reaction rates and the best selectivity were achieved using the 5,10-dihydro-5,10-dimethylphenazine radical cation. By means of fluorescence, UV-vis and EPR spectroscopy, a mechanism of the oxidative amine coupling, catalyzed by PhRCs, is proposed.
- Bri?ar, Rok,Unglaube, Felix,Hollmann, Dirk,Jiao, Haijun,Mejía, Esteban
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p. 13481 - 13490
(2018/11/02)
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- Tunable Ligand Effects on Ruthenium Catalyst Activity for Selectively Preparing Imines or Amides by Dehydrogenative Coupling Reactions of Alcohols and Amines
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Selective dehydrogenative synthesis of imines from a variety of alcohols and amines was developed by using the ruthenium complex [RuCl2(dppea)2] (6 a: dppea=2-diphenylphosphino-ethylamine) in the presence of catalytic amounts of Zn(OCOCF3)2 and KOtBu, whereas the selective dehydrogenative formation of amides from the same sources was achieved by using another ruthenium complex, [RuCl2{(S)-dppmp}2] [6 d: (S)-dppmp=(S)-2-((diphenylphosphenyl)methyl)pyrrolidine], in the presence of catalytic amounts of Zn(OCOCF3)2 and potassium bis(trimethylsilyl)amide (KHMDS). Our previously reported ruthenium complex, [Ru(OCOCF3)2(dppea)2] (8 a), was the catalyst precursor for the imine synthesis, whereas [Ru(OCOCF3)2{(S)-dppmp}2] (8 d), which was derived from the treatment of 6 d with Zn(OCOCF3)2 and characterized by single-crystal X-ray analysis, was the pre-catalyst for the amide formation. Control experiments revealed that the zinc salt functioned as a reagent for replacing chloride anions with trifluoroacetate anions. Plausible mechanisms for both selective dehydrogenative coupling reactions are proposed based on a time-course study, Hammett plot, and deuterium-labeling experiments.
- Higuchi, Takafumi,Tagawa, Risa,Iimuro, Atsuhiro,Akiyama, Shoko,Nagae, Haruki,Mashima, Kazushi
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p. 12795 - 12804
(2017/09/06)
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- Oxaziridine cleavage with a low-valent nickel complex: Competing C-O and C-N fragmentation from oxazanickela(II)cyclobutanes
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Reacting the low-valent nickel complex [(dtbpe)Ni]2(μ-η2:η2-C6H6) with oxaziridines was found to form mixtures of imine, amide and aldehyde products. If the N-substituent of the oxaziridine is sufficiently bulky, a short-lived intermediate can be isolated and characterized by X-ray diffraction studies as an oxazanickela(ii)cyclobutane. This is the first well-defined example of N-O oxidative addition of an oxaziridine to a transition metal. Subsequent fragmentation of this oxazanickelacyclobutane forms a complex mixture of products, including a nickel(ii) imido complex, demonstrating that oxaziridines can serve as nitrene precursors. Preliminary mechanistic analysis is consistent with a bimetallic mechanism of fragmentation of the oxazanickelacyclobutane to form the nickel imido and η2-aldehyde complexes.
- Desnoyer, Addison N.,Chiu, Weiling,Cheung, Candy,Patrick, Brian O.,Love, Jennifer A.
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supporting information
p. 12442 - 12445
(2017/11/22)
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- Polycyclic propargylamine and acetylene derivatives as multifunctional neuroprotective agents
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The aim of this study was to design drug-like molecules with multiple neuroprotective mechanisms which would ultimately inhibit N-methyl-d-aspartate (NMDA) receptors, block L-type voltage gated calcium channels (VGCC) and inhibit apoptotic processes as we
- Zindo, Frank T.,Barber, Quinton R.,Joubert, Jacques,Bergh, Jacobus J.,Petzer, Jacobus P.,Malan, Sarel F.
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p. 122 - 134
(2014/05/20)
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- Dehydrogenative synthesis of imines from alcohols and amines catalyzed by a ruthenium N-heterocyclic carbene complex
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A new method for the direct synthesis of imines from alcohols and amines is described where hydrogen gas is liberated. The reaction is catalyzed by the ruthenium N-heterocyclic carbene complex [RuCl2(IiPr)(p-cymene)] in the presence of the ligand DABCO and molecular sieves. The imination can be applied to a variety of primary alcohols and amines and can be combined with a subsequent addition reaction. A deuterium labeling experiment indicates that the catalytically active species is a ruthenium dihydride. The reaction is believed to proceed by initial dehydrogenation of the alcohol to the aldehyde, which stays coordinated to ruthenium. Nucleophilic attack of the amine affords the hemiaminal, which is released from ruthenium and converted into the imine.
- Maggi, Agnese,Madsen, Robert
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experimental part
p. 451 - 455
(2012/04/23)
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- Catalytic C-H bond amination from high-spin iron imido complexes
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Dipyrromethene ligand scaffolds were synthesized bearing large aryl (2,4,6-Ph3C6H2, abbreviated Ar) or alkyl ( tBu, adamantyl) flanking groups to afford three new disubstituted ligands (RL, 1,9-R2-5-mesityldipyrromethene, R = aryl, alkyl). While high-spin (S = 2), four-coordinate iron complexes of the type (RL)FeCl(solv) were obtained with the alkyl-substituted ligand varieties (for R = tBu, Ad and solv = THF, OEt2), use of the sterically encumbered aryl-substituted ligand precluded binding of solvent and cleanly afforded a high-spin (S = 2), three-coordinate complex of the type (ArL)FeCl. Reaction of (AdL)FeCl(OEt2) with alkyl azides resulted in the catalytic amination of C-H bonds or olefin aziridination at room temperature. Using a 5% catalyst loading, 12 turnovers were obtained for the amination of toluene as a substrate, while greater than 85% of alkyl azide was converted to the corresponding aziridine employing styrene as a substrate. A primary kinetic isotope effect of 12.8(5) was obtained for the reaction of (AdL)FeCl(OEt2) with adamantyl azide in an equimolar toluene/toluene-d8 mixture, consistent with the amination proceeding through a hydrogen atom abstraction, radical rebound type mechanism. Reaction of p-tBuC6H4N3 with (ArL)FeCl permitted isolation of a high-spin (S = 2) iron complex featuring a terminal imido ligand, (ArL)FeCl(N(p- tBuC6H4)), as determined by 1H NMR, X-ray crystallography, and 57Fe Moessbauer spectroscopy. The measured Fe-Nimide bond distance (1.768(2) A) is the longest reported for Fe(imido) complexes in any geometry or spin state, and the disruption of the bond metrics within the imido aryl substituent suggests delocalization of a radical throughout the aryl ring. Zero-field 57Fe Moessbauer parameters obtained for (ArL)FeCl(N(p- tBuC6H4)) suggest a FeIII formulation and are nearly identical with those observed for a structurally similar, high-spin FeIII complex bearing the same dipyrromethene framework. Theoretical analyses of (ArL)FeCl(N(p-tBuC 6H4)) suggest a formulation for this reactive species to be a high-spin FeIII center antiferromagnetically coupled to an imido-based radical (J = -673 cm-1). The terminal imido complex was effective for delivering the nitrene moiety to both C-H bond substrates (42% yield) as well as styrene (76% yield). Furthermore, a primary kinetic isotope effect of 24(3) was obtained for the reaction of (ArL)FeCl(N(p- tBuC6H4)) with an equimolar toluene/toluene-d8 mixture, consistent with the values obtained in the catalytic reaction. This commonality suggests the isolated high-spin Fe III imido radical is a viable intermediate in the catalytic reaction pathway. Given the breadth of iron imido complexes spanning several oxidation states (FeII-FeV) and several spin states (S = 0 → 3/2), we propose the unusual electronic structure of the described high-spin iron imido complexes contributes to the observed catalytic reactivity.
- King, Evan R.,Hennessy, Elisabeth T.,Betley, Theodore A.
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supporting information; experimental part
p. 4917 - 4923
(2011/05/16)
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- Catalytic C - H amination with unactivated amines through copper(II) amides
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En route to catalysis: Two equivalents of the three-coordinate copper(II) amide [(Cl2NN)Cu]-NHAd participate in stoichiometric C - H amination by a H-atom abstraction/radical capture sequence. This active species may be generated through a copper(II) tert-butoxide intermediate to allow for the unprecedented catalytic amination of sp3-C - H bonds with unactivated alkylamines. This method greatly expands the range of amines for catalytic C - H amination since most protocols require N-based electron-withdrawing groups.
- Wiese, Stefan,Badiei, Yosra M.,Gephart, Raymond T.,Mossin, Susanne,Varonka, Matthew S.,Melzer, Marie M.,Meyer, Karsten,Cundari, Thomas R.,Warren, Timothy H.
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supporting information; experimental part
p. 8850 - 8855
(2011/02/24)
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- C--H BOND AMINATION AND OLEFIN AZIRIDINATION WITH BETA-DIKETIMINATO COPPER CATALYSTS
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One aspect of the present invention relates to a method for the transition metal (e.g., Cu(I)) mediated amidation of C-H bonds using electron-rich aliphatic azides. In certain embodiments, the methods are useful for the C-H insertion of nitrenes generated and stabilized by a β-diketiminato metal catalyst. In certain embodiments, said nitrenes are generated from organoazides, or by oxidation of the corresponding amine. Another aspect of the present invention relates to olefin aziridination using said β-diketiminato metal catalysts. In addition, the methods of the present invention include stereoselective C-H bond aminations and olefin aziridinatons. In certain embodiments, the methods are conducted in an aerobic environment. In certain embodiments, the present invention relates to the use of O2 as an oxidant, wherein water is the byproduct of oxidation; this fact avoids the generation of toxic byproducts and renders the methods atom economical.
- -
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Page/Page column 17; 18
(2008/12/06)
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- The synthesis and evaluation of new α-hydrogen nitroxides for 'living' free radical polymerization
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Three N-alkoxyamines were synthesized for use in nitroxide-mediated radical polymerization. Upon thermolysis, they generate new acyclic α-hydrogen nitroxides: one adamantyl substituted and two diol-containing nitroxides. The initiators were tested in polymerization reactions in direct comparison with the initiator derived from the nitroxide TIPNO. Georg Thieme Verlag Stuttgart.
- Braslau, Rebecca,O'Bryan, Greg,Nilsen, Aaron,Henise, Jeff,Thongpaisanwong, Thanchanok,Murphy, Erin,Mueller, Laura,Ruehl, Jean
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p. 1496 - 1506
(2007/10/03)
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- Synthesis of α-aryl N-adamant-1-yl nitrones and using them for spin trapping of hydroxyl radicals
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α-Aryl N-adamant-1-yl nitrones were synthesized and evaluated with respect to the stability of the hydroxyl radical adduct. The polarity and water solubility of nitrones were altered with changing the α-aryl groups. Introduction of adamantane ring instead
- Sar, Cecilia P.,Hideg, Eva,Vass, Imre,Hideg, Kalman
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p. 379 - 384
(2007/10/03)
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- SYNTHESIS AND TRANSFORMATIONS OF N-ADAMANTYL-SUBSTITUTED OXAZIRIDINES
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N-Adamantyl-substituted oxaziridines were obtained by the oxidation of the Schiff bases synthesized from adamantyl-containing amines with peroxyacetic acid.The thermal rearrangement and fragmentation under the influence of Fe(II) ions, leading to nitrones
- Isaev, S. D.,Novoselov, E. F.,Yurchenko, A. G.
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p. 103 - 108
(2007/10/02)
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- Sterically Hindered Lithium Dialkylamides; A Novel Synthesis of Lithium Dialkylamides from N-t-Alkyl-N-benzylideneamines and the Isolation of Highly Hindered s-Alkyl-t-alkylamines
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The convenient synthesis of lithium amides from imines 1 and organolithium reagents, and the isolation of the related highly hindered dialkylamines 3 are described.
- Cliffe, Ian A.,Crossley, Roger,Shepherd, Robin G.
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p. 1138 - 1140
(2007/10/02)
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