- 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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- 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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- 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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- 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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- 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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- OXYSTEROLS AND METHODS OF USE THEREOF
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Compounds are provided according to Formula (I): and pharmaceutically acceptable salts thereof, and pharmaceutical compositions thereof; wherein R2, R3, R4, R5, and and R6 are as defined herein. Compounds of the present invention are contemplated useful for the prevention and treatment of a variety of conditions.
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Paragraph 00353; 00354; 00704
(2018/05/16)
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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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- Selective oxidation reactions of natural compounds with hydrogen peroxide mediated by methyltrioxorhenium
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We have investigated the oxidative behaviour of natural compounds such as methyl abietate (1), farnesyl acetate (2), a-ionone (3), β-ionone (4), methyl linolelaidate (5), methyl linolenate (6) and bergamottin (7) with the oxidant system methyltrioxo-rhenium/ H2O2/pyridine. The reactions, performed in CH2Cl2/H2O at 25 °C, have shown good regioand stereoselectivity. The oxidation products were isolated by HPLC or silica gel chromatography and characterized by MS(EI), 1H-, 13C-NMR, APT, gCOSY, HSQC, TOCSY and NOESY measurements. The selectivity seems to be controlled by the nucleophilicity of double bonds and by stereoelectronic and steric effects.
- Amato, Maria E.,Ballistreri, Francesco P.,Pappalardo, Andrea,Tomaselli, Gaetano A.,Toscano, Rosa M.,Sfrazzetto, Giuseppe Trusso
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supporting information
p. 13754 - 13763
(2014/01/06)
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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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- Process for producing optically active compound
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A process for producing an optically active compound based on the hydrolysis of an alkenyl ester compound or the cleavage of an alkenyl ether compound. The process uses neither an acidic compound nor a basic compound, and rectants can be reacted in a high concentration. It does not necessitate a buffer, nutrient, etc. unlike enzymatic reactions or reactions using a microorganism. It is a simple process which attains a satisfactory production efficiency. The process, which is for producing an optically active carboxylic acid or optically active alcohol represented by the general formula (VI): (wherein R1, R2, and R3 are different groups; and A represents methylene, carbonyl, or a single bound), is characterized by causing water to act on an alkenyl ester or alkenyl ether represented by the general formula (I): (wherein R4, R5, and R6 each represents hydrogen, alkyl, etc.) in the presence of a specific transition metal complex having an optically active ligand.
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Page/Page column 5
(2008/06/13)
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