- Isolation of a copper(I) triazolide: A "click" intermediate
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(Figure Presented) Click snapshot: In an aprotic medium, a copper(I) triazolide complex is synthesized from a sterically hindered copper acetylide and an organoazide (see scheme: yellow Cu, blue N, dark gray C, gray H). This result provides direct evidence for such a complex, which had previously been hypothesized.
- Nolte, Christoph,Mayer, Peter,Straub, Bernd F.
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Read Online
- New osmium-based reagent for the dihydroxylation of alkenes
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The cis dihydroxylation of alkenes is most efficiently accomplished by reaction with osmium tetroxide. Recently, the expense and toxicity of osmium tetroxide have led to a number of attempts to harness alternative osmium-based reagents, including microencapsulation and solid support techniques. We describe here the development of a new nonvolatile, stable, and recoverable osmium-based reagent devised for the stoichiometric cis dihydroxylation of alkenes. Although attempts to make this new dihydroxylation work with catalytic amounts of this reagent were unsuccessful, we did develop a sensitive test for free osmium tetroxide leached from the reagent in situ: this test may well have uses in probing future applications of derivatized osmium reagents.
- Donohoe, Timothy J.,Harris, Robert M.,Butterworth, Sam,Burrows, Jeremy N.,Cowley, Andrew,Parker, Jeremy S.
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Read Online
- Dilithium Amides as a Modular Bis-Anionic Ligand Platform for Iron-Catalyzed Cross-Coupling
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Dilithium amides have been developed as a bespoke and general ligand for iron-catalyzed Kumada-Tamao-Corriu cross-coupling reactions, their design taking inspiration from previous mechanistic and structural studies. They allow for the cross-coupling of alkyl Grignard reagents with sp2-hybridized electrophiles as well as aryl Grignard reagents with sp3-hybridized electrophiles. This represents a rare example of a single iron-catalyzed system effective across diverse coupling reactions without significant modification of the catalytic protocol, as well as remaining operationally simple.
- Neate, Peter G.N.,Zhang, Bufan,Conforti, Jessica,Brennessel, William W.,Neidig, Michael L.
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supporting information
p. 5958 - 5963
(2021/08/18)
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- Hydrosilylation and Mukaiyama aldol-type reaction of quinolines and hydrosilylation of imines catalyzed by a mesoionic carbene-stabilized borenium ion
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Aldimines and ketimines containing electron-donating and electron-withdrawing groups can be hydrosilylated with borenium catalysts at as low as 1 mol% catalyst loading at room temperature, providing the corresponding secondary amines in excellent yields. Reactions with 2-phenylquinoline gave the 1,4-hydrosilylquinoline product selectively which can be further functionalized in a one-pot synthesis to give unique γ-amino alcohol derivatives. Control experiments suggest that the borenium ion catalyzes both the hydrosilylation and subsequent addition to the aldehyde.
- Bestvater, Brian P.,Clarke, Joshua J.,Crudden, Cathleen M.,DeJesus, Joseph F.,Devaraj, Karthik,Eisenberger, Patrick,Kojima, Ryoto
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p. 6786 - 6791
(2021/08/20)
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- Synthesis of pentafluorobenzene-based NHC adducts and their catalytic activity in the microwave-assisted reactions of aldehydes
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N-Heterocyclic carbenes (NHCs) have been widely used in organometallic chemistry as ligands, as well as standalone organocatalysts in various reactions, mostly using aromatic aldehydes as substrates. We have previously demonstrated the efficiency of azolium-2-carboxylate zwitterions in the hydroxymethylation of aldehydes, especially aliphatic aldehydes, under microwave irradiation. In the present work, we report a series of pentafluorobenzene-based NHC adducts and their efficiency in the hydroxymethylation and self-condensation of aliphatic and aromatic aldehydes using microwave irradiation. The free carbenes are released under the reaction conditions and 1,3-dimesityl-2-(perfluorophenyl)imidazolidine and 1,3-bis(2,6-dimethylphenyl)-2-(perfluorophenyl)imidazolidine proved to be the most potent precatalysts.
- Papadaki, Evanthia,Magrioti, Victoria
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supporting information
(2019/12/24)
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- Mechanochemistry for facilitated access to N,N-diaryl NHC metal complexes
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A user-friendly and solvent-free mechanosynthetic strategy allowed light-sensitive silver(i) complexes featuring N,N-diaryl N-heterocyclic carbenes (NHC), including challenging and sterically hindered ligands, to be yielded efficiently. The first transmet
- Beillard, Audrey,Bantreil, Xavier,Métro, Thomas-Xavier,Martinez, Jean,Lamaty, Frédéric
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supporting information
p. 1057 - 1063
(2017/02/10)
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- Addition of E-H (E = N, P, C, O, S) Bonds to Heterocumulenes Catalyzed by Benzimidazolin-2-iminato Actinide Complexes
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The synthesis and characterization of benzimidazolin-2-iminato actinide(IV) complexes [(BimR1/R2N)An(N{SiMe3}2)3] (An = U, Th) (1-6) is reported. All complexes were obtained in high yields, and their solid state structures were established through single-crystal X-ray diffraction analysis. Using 1-6 as precatalysts, the addition of mono- and bifunctional E-H (E = N, P, C, O, S) substrates to various heterocumulenes, including carbodiimides, isocyanates, and isothiocyanates, was investigated, affording the respective addition products in high yields under very mild reaction conditions. Various amines were applicable to this reaction, indicating a large scope capability of amine nucleophiles for the insertion process.
- Liu, Heng,Fridman, Natalia,Tamm, Matthias,Eisen, Moris S.
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supporting information
p. 3896 - 3903
(2017/10/30)
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- Keto-Enol Thermodynamics of Breslow Intermediates
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Breslow intermediates, first postulated in 1958, are pivotal intermediates in carbene-catalyzed umpolung. Attempts to isolate and characterize these fleeting amino enol species first met with success in 2012 when we found that saturated bis-Dipp/Mes imida
- Paul, Mathias,Breugst, Martin,Neud?rfl, J?rg-Martin,Sunoj, Raghavan B.,Berkessel, Albrecht
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supporting information
p. 5044 - 5051
(2016/05/19)
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- Transfer Hydrogenation of Nitriles, Olefins, and N-Heterocycles Catalyzed by an N-Heterocyclic Carbene-Supported Half-Sandwich Complex of Ruthenium
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In the presence of KOBut, N-heterocyclic carbene-supported half-sandwich complex [Cp(IPr)Ru(pyr)2][PF6] (3) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) catalyzes transfer hydrogenation (TH) of nitriles, activated N-heterocycles, olefins, and conjugated olefins in isopropanol at the catalyst loading of 0.5%. The TH of nitriles leads to imines, produced as a result of coupling of the initially formed amines with acetone (produced from isopropanol), and showed good chemoselectivity. Reduction of N-heterocycles occurs for activated polycyclic substrates (e.g., quinoline) and takes place exclusively in the heterocycle. The TH also works well for linear and cyclic olefins but fails for trisubstituted substrates. However, the C = C bond of α,β-unsaturated esters, amides, and acids is easily reduced even for trisubstituted species, such as isovaleriates. Mechanistic studies suggest that the active species in these catalytic reactions is the trihydride Cp(IPr)RuH3 (5), which can catalyze these reactions in the absence of any base. Kinetic studies are consistent with a classical inner sphere hydride-based mechanism of TH.
- Mai, Van Hung,Nikonov, Georgii I.
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p. 943 - 949
(2016/05/09)
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- A direct and practical approach for the synthesis of N-heterocyclic carbene coinage metal complexes
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A novel direct and practical synthetic route leading to N-heterocyclic carbene coinage metal complexes has been developed by using air stable, commercial available Au(III) salt [MAuCl4·2H2O], CuCln (n=1,2) or AgCl, and imidazolium salts as starting materials. The reaction proceeded without sacrificing carbene transfer agent (Ag 2O) or using highly sensitive free NHC.
- Zhu, Shifa,Liang, Renxiao,Jiang, Huanfeng
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supporting information; experimental part
p. 7949 - 7955
(2012/09/22)
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- Controlled acrylate insertion regioselectivity in diazaphospholidine- sulfonato palladium(II) complexes
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Diazaphospholidine-sulfonato Pd(II) complexes [{κ2-P,O-(N- Ar2C2H4N2P)C6H 4SO3}PdMe(L)] 1-L (L = dmso, pyridine, lutidine, or μ-LiCl(solvent); 1a: Ar = Ph, 1b: Ar = 2-MeC6H4, 1c: Ar = 2-MeOC6H4, 1d: Ar = 2,4,6-Me3C 6H2, 1e: Ar = 2,6-iPr2C6H 3, 1f: Ar = 2,6-(p-tolyl)2C6H3) were prepared and structurally characterized. The regioselectivity of methyl acrylate (MA) insertion into the Pd-Me bond is entirely inverted from >93% 1,2-insertion for bulky substituents (1d-f, yielding the insertion products [(PO)Pd{κ2-C,O-CH2CHMeC(O)OMe], 12) to the usual electronically controlled 2,1-insertion (>95%) for the less bulky Ar = Ph (1a, yielding the insertion product [(PO)Pd{κ2-C,O- CHEtC(O)OMe], 11, and β-H elimination product methyl crotonate). DFT studies underline that this is due to a more favorable insertion transition state (2,1- favored by 12 kJ mol-1 over 1,2- for 1a) vs destabilization of the 2,1-insertion transition state in 1d,e. By contrast, MA insertion into the novel isolated and structurally characterized hydride and deuteride complexes [{κ2-P,O-(N-Ar2C 2H4N2P)C6H4SO 3}PdR(lutidine)] (Ar = 2,6-iPr2C6H3; 9e: R = H, 10e: R = D) occurs 2,1-selectively. This is due to the insertion occurring from the isomer with the P-donor and the olefin in trans arrangement, rather than the insertion into the alkyl from the cis isomer in which the olefin is in proximity to the bulky diazaphospholidine. 1a-f are precursors to active catalysts for ethylene polymerization to highly linear polyethylene with M n up to 35 000 g mol-1. In copolymerization experiments, norbornene was incorporated in up to 6.1 mol % into the polyethylene backbone.
- Wucher, Philipp,Roesle, Philipp,Falivene, Laura,Cavallo, Luigi,Caporaso, Lucia,Goettker-Schnetmann, Inigo,Mecking, Stefan
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p. 8505 - 8515
(2013/02/23)
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- Structure-Analytical Investigations of P-Substituted 1,3,2- Diazaphospholidines
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2-Diphenylphosphanyl-1,3,2-diazaphospholidines were prepared via metathesis from 2-chloro-1,3,2-diazaphospholidines and LiPPh2. For some of the products, symmetrisation to tetraphenyldiphosphane and 2,2′-bis-1,3,2- diazaphospholidinyls was observed. Most of the derivatives were characterised by single-crystal X-ray diffraction, which showed that all compounds studied feature elongated exocyclic P-Cl or P-P-bonds, respectively. The extent of this bond lengthening is in the P-phosphanyl-substituted species similar and in the P-chloro-derivatives less pronounced than in corresponding CC-unsaturated 1,3,2-diazaphospholenes. Structure correlation involving comparison of exocyclic P-X and endocyclic P-N distances suggests that n(N)/σ(P-X) hyperconjugation contributes strongly to the bond lengthening and induces a perceptible weakening of the P-P bonds in 2-diphenylphosphanyl-1,3,2- diazaphospholidines, which should render these compounds interesting substrates for P-P bond activation reactions. Copyright
- Puntigam, Oliver,Hajdok, Imre,Nieger, Martin,Niemeyer, Mark,Strobel, Sabine,Gudat, Dietrich
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scheme or table
p. 988 - 994
(2011/09/12)
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- Thiadiazolidine 1-oxide systems for phosphine-free palladium-mediated catalysis
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We herein report several highly active catalyst systems with thiadiazolidine 1-oxides as ligands for palladium in the Mizoroki-Heck reaction. Excellent yields of stilbenes derived from aryl iodides and bromides have been achieved using as little as 0.00002 mol % catalyst. The ligand/palladium system can be stored as a stock solution open to air at room temperature with no observable loss of activity for a period of several months.
- Buckley, Benjamin R.,Neary, Stephen P.
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experimental part
p. 7988 - 7994
(2010/10/21)
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- Probing the efficiency of N-heterocyclic carbene promoted O- to C-carboxyl transfer of oxazolyl carbonates
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(Chemical Equation Presented) Screening of a range of azolium salts, bases and solvents for reactivity indicates that triazolinylidenes, generated in situ with KHMDS in THF, promote the Steglich rearrangement of oxazolyl carbonates with high catalytic efficiency (typical reaction time 5 min at 1.5 mol % NHC). This protocol shows wide substrate applicability, even allowing the efficient generation of vicinal quaternary centers. An improved experimental procedure is also described that allows a simplified one-pot reaction protocol to be employed with similarly high catalytic efficiency.
- Thomson, Jennifer E.,Campbell, Craig D.,Concellon, Carmen,Duguet, Nicolas,Rix, Kathryn,Slawin, Alexandra M. Z.,Smith, Andrew D.
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p. 2784 - 2791
(2008/09/20)
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- N-Heterocyclic phosphenium cations: Syntheses and cycloaddition reactions
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A series of trifluoromethanesulfonate (OTf) salts of N-heterocyclic phospheniums (NHP) bearing phenyl (1a), para-methoxyphenyl (1b), 2,6-diisopropylphenyl (1c) and mesityl (1d) substituents is reported. The compounds 1b-d are made by a modification to a literature procedure that improves the overall yields for 1c and 1d by 15 and 23%, respectively. Two unwanted side-products in the synthesis of 1d, the diammonium salt, [(2,6-iPr-C6H3)N(H)2CH2CH 2N(H)2(2,6-iPr-C6H3)]Cl2 (4) and the bisphosphine (2,6-iPr-C6H3)N(PCl 2)CH2CH2N(PCl2)(2,6-iPr-C 6H3) (5), are crystallographically characterized, as is the intermediate cyclic chlorophosphine, C1PN(4-OMe-C6H 4)CH2CH2N(4-OMe-C6H4) (3b). The phenyl-substituted NHP 1a is fully characterized, including by X-ray crystallography, for the first time; this compound contains a short P-O contact of 2.1850(14) A Cycloaddition reactions of 1a-d with 2,3-dimethyl-1,3- butadiene give the expected spirocyclic phospholeniums, 7,8-dimethyl-1,4-diaryl- 1,4-diaza-5-phopshoniaspiro[4.4]non-7-ene, as their OTf salts (6a-d), while reactions with N,N′-dimesityl-1,4-diaza-1,3-butadiene give, except in the case of 1c, which is too bulky to react, the aza analogues, 1,4-dimesityl-6,9- diaryl-1,4,6,9-tetraaza-5-phosphoniaspiro[4.4]non-2-ene (7a, 7b and 7d). The sterically congested 7d is in thermal equilibrium with 1d and free diazadiene, and undergoes a substitution reaction with 2,3-dimethyl-1,3-butadiene to give 6d.
- Caputo, Christine A.,Price, Jacquelyn T.,Jennings, Michael C.,McDonald, Robert,Jones, Nathan D.
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p. 3461 - 3469
(2008/09/21)
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- Amination reactions of aryl halides with nitrogen-containing reagents mediated by palladium/imidazolium salt systems
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Nucleophilic N-heterocyclic carbenes have been conveniently used as catalyst modifiers in amination reactions involving aryl chlorides, aryl bromides, and aryl iodides with various nitrogen-containing substrates. The scope of a coupling process using a Pd(0) or Pd(II) source and an imidazolium salt in the presence of a base, KOtBu or NaOH, was tested using various substrates. The Pd2(dba)3/IPr·HCl (1, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) system presents the highest activity with respect to electron-neutral and electron-rich aryl chlorides. The ligand is also effective for the synthesis of benzophenone imines, which can be easily converted to the corresponding primary amines by acid hydrolysis. Less reactive indoles were converted to N-aryl-substituted indoles using as supporting ligand the more donating SIPr·HCl (5, SIPr = 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene). The Pd(OAc)2/SIPr·HCl/NaOH system is efficient for the N-arylation of diverse indoles with aryl bromides. The general protocol developed has been applied successfully to the synthesis of a key intermediate in the synthesis of an important new antibiotic. Mechanistically, palladium-to-ligand ratio studies strongly support an active species bearing one nucleophilic carbene ligand.
- Grasa,Viciu,Huang,Nolan
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p. 7729 - 7737
(2007/10/03)
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- Synthesis and activity of a new generation of ruthenium-based olefin metathesis catalysts coordinated with 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene ligands.
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[formula: see text] A new family of 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene-substituted ruthenium-based complexes 9a-c has been prepared starting from RuCl2(=CHPh)(PCy3)2 2. These air- and water-tolerant complexes were shown to exhibit an increased ring-closing metathesis activity at elevated temperature when compared to that of the parent complex 2 and the previously developed complex 3. In many instances the activity of these complexes also rivaled or exceeded that of the alkoxy-imido molybdenum complex 1. Catalyst loadings of as low as 0.05 mol% could be used.
- Scholl,Ding,Lee,Grubbs
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p. 953 - 956
(2008/02/09)
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