- Cobalt-Catalyzed Intermolecular Hydroamination of Unactivated Alkenes Using NFSI as Nitrogen Source
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Cheap metal (Fe, Mn, and Co)-catalyzed hydroamination of alkenes has been an attractive method for synthesis of amines because of biocompatibility of metal, excellent Markovnikov selectivity and chemoselectivity. However, most reports are limited to unsaturated nitrogen sources (nitric oxide, azos, azides, cyano, etc.), for which aminated products are very limited. Notably, while used widely for fluorinating reaction, N-fluorobenzenesulfonimide (NFSI) as amine source for hydroamination has seldom been reported. Here we developed a cobalt-catalyzed intermolecular hydroamination of unactivated alkenes using NFSI as nitrogen source under mild conditions. The reaction exhibits excellent chemo- and regio-selectivity with no hydrofluorination or linear-selectivity products. Notably, the reaction proceeded with excellent yield even though the amount of Co(salen) catalyst was reduced to 0.2 mol%. Recently, a similar work was also reported by Zhang and coworkers (ref. 19).
- Li, Linshan,Li, Yuxin,Li, Zhengming,Sun, Peng-Wei,Wang, Xinyao,Zhang, Ze
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- Cobalt-Mediated Switchable Catalysis for the One-Pot Synthesis of Cyclic Polymers
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A cobalt salen pentenoate complex [salen=(R,R)-N,N′-bis(3,5-di-tertbutylsalicylidene)-1,2-cyclohexanediamine] is rationally designed as the catalyst for the ring-opening copolymerization (ROCOP) of epoxides/anhydrides/CO2. Via migratory insertion of carbon monoxide (CO) into the Co?O bonds, the ROCOP-active species α-alkene-ω-O-CoIII(salen) can be rapidly and quantitatively transformed into α-alkene-ω-O2C-CoIII(salen) telechelic linear precursors. Upon dilution of reaction mixtures, the homolytic cleavage of Co?C bonds induced by visible light generates α-alkene acyl radicals that spontaneously undergo intramolecular radical addition to afford organocobalt-functionalized cyclic polyesters and CO2-based polycarbonates with excellent regioselectivity. The cyclic products can either react with radical scavengers to generate metal-free cyclic polymers or serve as photo-initiators for organometallic-mediated radical polymerization (OMRP) to produce tadpole-shaped copolymers.
- Lam, Jacky W. Y.,Liao, Can,Tang, Ben Zhong,Wang, Xianhong,Wang, Yong,Xie, Xiaolin,Zhao, Yajun,Zhou, Xingping,Zhu, Shuaishuai
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supporting information
p. 16974 - 16979
(2021/06/28)
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- Switchable Polymerization Triggered by Fast and Quantitative Insertion of Carbon Monoxide into Cobalt–Oxygen Bonds
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A strategy that uses carbon monoxide (CO) as a molecular trigger to switch the polymerization mechanism of a cobalt Salen complex [salen=(R,R)-N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine] from ring-opening copolymerization (ROCOP) of ep
- Poli, Rinaldo,Wang, Yong,Xie, Xiaolin,Xu, Jing,Zhao, Yajun,Zhou, Xingping,Zhu, Shuaishuai
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supporting information
p. 5988 - 5994
(2020/02/25)
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- Oxygen-Triggered Switchable Polymerization for the One-Pot Synthesis of CO2-Based Block Copolymers from Monomer Mixtures
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Switchable polymerization provides the opportunity to regulate polymer sequence and structure in a one-pot process from mixtures of monomers. Herein we report the use of O2 as an external stimulus to switch the polymerization mechanism from the
- Zhao, Yajun,Wang, Yong,Zhou, Xingping,Xue, Zhigang,Wang, Xianhong,Xie, Xiaolin,Poli, Rinaldo
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supporting information
p. 14311 - 14318
(2019/08/30)
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- Selective H2O2 oxidation of organic sulfides to sulfoxides catalyzed by cobalt(III)-salen ion
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Abstract The catalytic activity of cobalt(III)-salen ion catalyzed selective H2O2 oxidation of organic sulfides to sulfoxides is examined using spectrophotometric technique. The catalytic reaction proceeds through Michaelis-Menten kinetics and the rate of the reaction is highly sensitive to the nature of the substituent present in the substrate as well as in the salen ligand. The product analyses show that the aryl methyl sulfides are selectively oxidized to the corresponding sulfoxides. Based on the spectral and kinetic studies two possible mechanisms have been proposed.
- Mary Imelda Jayaseeli,Ramdass, Arumugam,Rajagopal, Seenivasan
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- Tuning ligand electronics and peripheral substitution on cobalt salen complexes: Structure and polymerisation activity
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A series of cobalt salen complexes, where salen represents an N 2O2 bis-Schiff-base bis-phenolate framework, are prepared, characterised and investigated for reversible-termination organometallic mediated radical polymerisation (RT-OMRP). The salen ligands contain a cyclohexane diimine bridge and systematically altered para-substituted phenoxide moieties as a method to examine the electronic impact of the ligand on complex structure and reactivity. The complexes are characterised by single crystal X-ray diffraction, cyclic voltammetry, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy and computational methods. Structural studies all support a tailorable metal centre reactivity altered by the electron-donating ability of the salen ligand. RT-OMRP of styrene, methyl methacrylate and vinyl acetate is reported and suggests that cobalt-carbon bond strength varies with the ligand substitution. Competing β-hydrogen abstraction affords long-chain olefin-terminated polymer chains and well controlled vinyl acetate polymerisations, contrasting with the lower temperature associative exchange mechanism of degenerative transfer OMRP.
- Chiang, Linus,Allan, Laura E. N.,Alcantara, Juan,Wang, Michael C. P.,Storr, Tim,Shaver, Michael P.
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p. 4295 - 4304
(2014/03/21)
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- Mechanistic basis for high stereoselectivity and broad substrate scope in the (salen)Co(III)-catalyzed hydrolytic kinetic resolution
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In the (salen)Co(III)-catalyzed hydrolytic kinetic resolution (HKR) of terminal epoxides, the rate- and stereoselectivity-determining epoxide ring-opening step occurs by a cooperative bimetallic mechanism with one Co(III) complex acting as a Lewis acid and another serving to deliver the hydroxide nucleophile. In this paper, we analyze the basis for the extraordinarily high stereoselectivity and broad substrate scope observed in the HKR. We demonstrate that the stereochemistry of each of the two (salen)Co(III) complexes in the rate-determining transition structure is important for productive catalysis: a measurable rate of hydrolysis occurs only if the absolute stereochemistry of each of these (salen)Co(III) complexes is the same. Experimental and computational studies provide strong evidence that stereochemical communication in the HKR is mediated by the stepped conformation of the salen ligand, and not the shape of the chiral diamine backbone of the ligand. A detailed computational analysis reveals that the epoxide binds the Lewis acidic Co(III) complex in a well-defined geometry imposed by stereoelectronic rather than steric effects. This insight serves as the basis of a complete stereochemical and transition structure model that sheds light on the reasons for the broad substrate generality of the HKR.
- Ford, David D.,Nielsen, Lars P. C.,Zuend, Stephan J.,Musgrave, Charles B.,Jacobsen, Eric N.
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supporting information
p. 15595 - 15608
(2013/11/06)
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- Efficient resolution of racemic N-benzyl β3-amino acids by iterative liquid-liquid extraction with a chiral (salen)cobalt(iii) complex as enantioselective selector
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The efficient (up to 93% ee) resolution of racemic N-benzyl β3-amino acids has been achieved by an iterative (two cycle) liquid-liquid extraction process using a lipophilic chiral (salen)cobalt(iii) complex [CoIII(1)(OAc)]. As a result of the resolution by extraction, one enantiomer of the N-benzyl β3-amino acid predominated in the aqueous phase, while the other enantiomer was driven into the organic phase by complexation to cobalt. The complexed amino acid was then quantitatively released into an aqueous phase, by a reductive (CoIII → Co II) counter-extraction using l-ascorbic acid. The reductive cleavage allowed for the recovery of the cobalt(ii) selector in up to 90% yield (easily re-oxidable to CoIII with air/AcOH). The Royal Society of Chemistry.
- Dzygiel, Pawel,Monti, Chiara,Piarulli, Umberto,Gennari, Cesare
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p. 3464 - 3471
(2008/09/20)
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- A practical approach to the resolution of racemic N-benzyl α-amino acids by liquid-liquid extraction with a lipophilic chiral salen-cobalt(III) complex
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(Chemical Equation Presented) Liquidating the assets: Coordination of one enantiomer from a racemic mixture of N-benzyl α-amino acids (N-Bn-AA) to the lipophilic chiral [CoIII(salen)(OAc)] complex results in its extraction into the organic phas
- Reeve, Toby B.,Cros, Jean-Philippe,Gennari, Cesare,Piarulli, Umberto,De Vries, Johannes G.
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p. 2449 - 2453
(2007/10/03)
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- Catalytic activity of salenCo(III)OAc complex in the reaction of addition of carboxylic acids to terminal epoxides
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The catalytic activity and regioselectivity were studied of the salenCo(III)OAc complex in the reaction of addition of aliphatic carboxylic acids to a series of terminal epoxides (epichlorohydrin, 1,2-epoxybutane, propylene oxide, tert-butyl glycidyl ether and 2,3-epoxypropyl phenyl ether). The reduction in the activity in the order: acetic > acrylic > methacrylic acid was found. The regioselectivity of the addition was independent on carboxylic acid nature and depended on the nature of the epoxide. The best regioselectivity for the addition to epichlorohydrin was observed. The catalytic activity and regioselectivity of salenCo(III)OAc were compared with those for chromium(III) acetate catalyst. The catalytic activity and regioselectivity were studied of the salenCo(III)OAc complex in the reaction of addition of aliphatic carboxylic acids (2) to a series of terminal epoxides (3). The reduction in the activity in the order: acetic > acrylic > methacrylic acid was found. The regioselectivity of the addition was independent on carboxylic acid nature and depended on the nature of the epoxide.
- Bukowska, Agnieszka,Bukowski, Wiktor,Noworól, Jaros?aw
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- Highly selective hydrolytic kinetic resolution of terminal epoxides catalyzed by chiral (salen)CoIII complexes. Practical synthesis of enantioenriched terminal epoxides and 1,2-diols
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The hydrolytic kinetic resolution (HKR) of terminal epoxides catalyzed by chiral (salen)CoIII complex 1·OAc affords both recovered unreacted epoxide and 1,2-diol product in highly enantioenriched form. As such, the HKR provides general access to useful, highly enantioenriched chiral building blocks that are otherwise difficult to access, from inexpensive racemic materials. The reaction has several appealing features from a practical standpoint, including the use of H2O as a reactant and low loadings (0.2-2.0 mol %) of a recyclable, commercially available catalyst. In addition, the HKR displays extraordinary scope, as a wide assortment of sterically and electronically varied epoxides can be resolved to ≥ 99% ee. The corresponding 1,2-diols were produced in good-to-high enantiomeric excess using 0.45 equiv of H2O. Useful and general protocols are provided for the isolation of highly enantioenriched epoxides and diols, as well as for catalyst recovery and recycling. Selectivity factors (krel) were determined for the HKR reactions by measuring the product ee at ca. 20% conversion. In nearly all cases, krel values for the HKR exceed 50, and in several cases are well in excess of 200.
- Schaus, Scott E.,Brandes, Bridget D.,Larrow, Jay F.,Tokunaga, Makoto,Hansen, Karl B.,Gould, Alexandra E.,Furrow, Michael E.,Jacobsen, Eric N.
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p. 1307 - 1315
(2007/10/03)
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- Synthesis and enantioselective Diels-Alder reactions of optically active cobalt(III) salen-1,3-butadien-2-yl complexes
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The syntheses of two optically active Co(salen)-1,3-butadien-2-yl complexes are reported. One of the dienyl complexes was characterized by X-ray crystallography. The dienyl complexes underwent Diels-Alder reactions with high enantioselectivity with dimethyl fumarate. A highlight of this chemistry is that Diels-Alder cycloadduct cobalt complexes were cleanly cleaved at the cobalt-carbon bond with concomitant optically active cobalt complex starting material and optically active cyclohexene cycloadduct recovery.
- Chapman,Day,Welker
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p. 1615 - 1618
(2008/10/08)
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- Aerobic epoxidation via alkyl-2-oxocyclopentanecarboxylate co-oxidation with cobalt or manganese Jacobsen-type catalysts
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In the presence of methyl, tert-butyl, or (-)-menthyl esters of 2-oxocyclopentanecarboxylic acids Jacobsen-type complexes of cobalt(II) and manganese(III) form active catalysts for alkene epoxidation using molecular oxygen. Alkyl-1-hydroxy-2-oxocyclopentanecarboxylates and 1-alkyl-2-oxo-hexanedicarboxylic acids are formed as co-oxidation products. The (-)-menthyl/cobalt system is selective for epoxide production but the products are racemic consistent with radical epoxidation in solution rather than at the cobalt complex. The manganese Jacobsen-type complex gives lower yields of epoxides (40-60%) but for 2,2-dimethylchromene and styrene these are optically active (12-60% ee).
- Rhodes, Barry,Rowling, Simon,Tidswell, Peter,Woodward, Simon,Brown, Stephen M.
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p. 375 - 384
(2008/10/09)
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