349-75-7Relevant academic research and scientific papers
Evidence for the Incursion of Intermediates in the Hydrolysis of Tertiary, Secondary, and Primaty Substrates
Blandamer, Michael Jesse,Robertson, Ross Elmore,Scott, John Marshall William,Vrielink, Alice
, p. 2585 - 2592 (1980)
The temperature dependence related to a series of solvolytic displacement reactions of primary, secondary, and tertiary carbon centers are examined using a new equation.The equation is derived by integrating the van't Hoff isochore in a form related to the absolute rate theory on the assumption that the heat capacity of activation (ΔGp) is constant.Unexpectedly, the new equation is capable of correctly sensing changes in ΔCp with temperature.The new equation is used to show that in some instances ΔCp is partly abnormal and derives from the nonunitary nature of the displacement in a way outlined previously by Albery and Robinson.The significance of this new mechanistic tool is considered in relation to the displacement reaction of 2-bromopropane in heavy water and the reactions of adamantyl nitrate, tert-butyl chloride, S-propyl methanesulphonate, m-trifluoromethylbenzyl nitrate, and ethyl bromide with ordinary water.
Nickel(II) Catalyzed Hydroboration: A Route to Selective Reduction of Aldehydes and N-Allylimines
Hossain, Istiak,Schmidt, Joseph A. R.
, p. 1877 - 1884 (2020/05/25)
A cationic [(iminophosphine)nickel(allyl)]+ complex was found to be sufficiently electrophilic to activate aldehydes and N-allylimines to undergo hydroboration with pinacolborane (HBpin) under mild reaction conditions. The catalyst displayed excellent selectivity toward aldehydes in the presence of ketones. A wide variety of functional groups were tolerated, including halogens, NO2, CN, OMe, and alkenes for both aldehydes and imines. Electron-rich substrates were found to be significantly more reactive than their electron poor counterparts, a feature that was correlated to their enhanced ability to coordinate to the Lewis acidic nickel center.
Cerium(IV) Carboxylate Photocatalyst for Catalytic Radical Formation from Carboxylic Acids: Decarboxylative Oxygenation of Aliphatic Carboxylic Acids and Lactonization of Aromatic Carboxylic Acids
Hirosawa, Keishi,Mashima, Kazushi,Satoh, Tetsuya,Shinohara, Koichi,Shirase, Satoru,Tamaki, Sota,Tsurugi, Hayato
supporting information, (2020/03/25)
We found that in situ generated cerium(IV) carboxylate generated by mixing the precursor Ce(OtBu)4 with the corresponding carboxylic acids served as efficient photocatalysts for the direct formation of carboxyl radicals from carboxylic acids under blue light-emitting diodes (blue LEDs) irradiation and air, resulting in catalytic decarboxylative oxygenation of aliphatic carboxylic acids to give C-O bond-forming products such as aldehydes and ketones. Control experiments revealed that hexanuclear Ce(IV) carboxylate clusters initially formed in the reaction mixture and the ligand-to-metal charge transfer nature of the Ce(IV) carboxylate clusters was responsible for the high catalytic performance to transform the carboxylate ligands to the carboxyl radical. In addition, the Ce(IV) carboxylate cluster catalyzed direct lactonization of 2-isopropylbenzoic acid to produce the corresponding peroxy lactone and ?3-lactone via intramolecular 1,5-hydrogen atom transfer (1,5-HAT).
Polypyridyl iridium(III) based catalysts for highly chemoselective hydrogenation of aldehydes
Pandrala, Mallesh,Resendez, Angel,Malhotra, Sanjay V.
, p. 283 - 288 (2019/09/30)
Iridium-catalyzed transfer hydrogenation (TH) of carbonyl compounds using HCOOR (R = H, Na, NH4) as a hydrogen source is a pivotal process as it provides the clean process and is easy to execute. However, the existing highly efficient iridium catalysts work at a narrow pH; thus, does not apply to a wide variety of substrates. Therefore, the development of a new catalyst which works at a broad pH range is essential as it can gain a broader scope of utilization. Here we report highly efficient polypyridyl iridium(III) catalysts, [Ir(tpy)(L)Cl](PF6)2 {where tpy = 2,2′:6′,2′'-Terpyridine, L = phen (1,10-Phenanthroline), Me2phen (4,7-Dimethyl-1,10-phenanthroline), Me4phen (3,4,7,8-Tetramethyl-1,10-phenanthroline), Me2bpy (4,4′-Dimethyl-2–2′-dipyridyl)} for the chemoselective reduction of aldehydes to alcohols in aqueous ethanol and sodium formate as the hydride source. The reaction can be carried out efficiently in broad pH ranges, from pH 6 to 11. These catalysts are air stable, easy to prepare using commercially available starting materials, and are highly applicable for a wide range of substrates, such as electron-rich or deficient (hetero)arenes, halogens, phenols, alkoxy, ketones, esters, carboxylic acids, cyano, and nitro groups. Particularly, acid and hydroxy groups containing aldehydes were reduced successfully in basic and acidic reaction conditions, demonstrating the efficiency of the catalyst in a broad pH range with high conversion rates under microwave irradiation.
Study of Precatalyst Degradation Leading to the Discovery of a New Ru0 Precatalyst for Hydrogenation and Dehydrogenation
Anaby, Aviel,Schelwies, Mathias,Schwaben, Jonas,Rominger, Frank,Hashmi, A. Stephen K.,Schaub, Thomas
supporting information, p. 2193 - 2201 (2018/07/25)
The complex Ru-MACHO (1) is a widely used precatalyst for hydrogenation and dehydrogenation reactions under basic conditions. In an attempt to identify the active catalyst form, 1 was reacted with a strong base. The formation of previously unreported species was observed by NMR and mass spectrometry. This observation indicated that complex 1 quickly degraded under basic conditions when no substrate was present. X-ray crystallography enabled the identification of three complexes as products of this degradation of complex 1. These complexes suggested degradation pathways which included ligand cleavage and reassembly, along with reduction of the ruthenium atom. One of the decomposition products, the Ru0 complex [Ru(N(CH2CH2PPh2)3)CO] (5), was prepared independently and studied. 5 was found to be active, entirely additive-free, in the acceptorless dehydrogenation of aliphatic alcohols to esters. The hydrogenation of esters catalyzed by 5 was also demonstrated under base-free conditions with methanol as an additive. Protic substrates were shown to add reversibly to complex 5, generating RuII-hydrido species, thus presenting a rare example of reversible oxidative addition from Ru0 to RuII and reductive elimination from RuII to Ru0.
Triazolylidene Iridium Complexes for Highly Efficient and Versatile Transfer Hydrogenation of C=O, C=N, and C=C Bonds and for Acceptorless Alcohol Oxidation
Mazloomi, Zahra,Pretorius, René,Pàmies, Oscar,Albrecht, Martin,Diéguez, Montserrat
, p. 11282 - 11298 (2017/09/25)
A set of iridium(I) and iridium(III) complexes is reported with triazolylidene ligands that contain pendant benzoxazole, thiazole, and methyl ether groups as potentially chelating donor sites. The bonding mode of these groups was identified by NMR spectroscopy and X-ray structure analysis. The complexes were evaluated as catalyst precursors in transfer hydrogenation and in acceptorless alcohol oxidation. High-valent iridium(III) complexes were identified as the most active precursors for the oxidative alcohol dehydrogenation, while a low-valent iridium(I) complex with a methyl ether functionality was most active in reductive transfer hydrogenation. This catalyst precursor is highly versatile and efficiently hydrogenates ketones, aldehydes, imines, allylic alcohols, and most notably also unpolarized olefins, a notoriously difficult substrate for transfer hydrogenation. Turnover frequencies up to 260 h-1 were recorded for olefin hydrogenation, whereas hydrogen transfer to ketones and aldehydes reached maximum turnover frequencies greater than 2000 h-1. Mechanistic investigations using a combination of isotope labeling experiments, kinetic isotope effect measurements, and Hammett parameter correlations indicate that the turnover-limiting step is hydride transfer from the metal to the substrate in transfer hydrogenation, while in alcohol dehydrogenation, the limiting step is substrate coordination to the metal center.
Cooperative interplay between a flexible PNN-Ru(II) complex and a NaBH4 additive in the efficient catalytic hydrogenation of esters
Wang, Zheng,Chen, Xiangyang,Liu, Bo,Liu, Qing-Bin,Solan, Gregory A.,Yang, Xinzheng,Sun, Wen-Hua
, p. 1297 - 1304 (2017/05/05)
A catalyst loading of between 0.001-0.05 mol% of the PNN-bearing ruthenium(II) complex [fac-PNN]RuH(PPh3)(CO) (PNN = 8-(2-diphenylphosphinoethyl)amidotrihydroquinoline), in combination with 5 mol% NaBH4, efficiently catalyzes the hydrogenation of esters to their corresponding alcohols under mild pressures of hydrogen. Both aromatic and aliphatic esters can be converted with high values of TON or TOF achievable. Mechanistic investigations using both DFT calculations and labeling experiments highlight the cooperative role of NaBH4 in the catalysis while the catalytically active species has been established as trans-dihydride [mer-PNHN]RuH2(CO) (PNHN = 8-(2-diphenylphosphinoethyl)aminotrihydroquinoline). The stereo-structure of the PNHN-ruthenium species greatly affects the activity of the catalyst, and indeed the cis-dihydride isomer [fac-PNHN]RuH2(CO) is unable to catalyze the hydrogenation of esters until ligand reorganization occurs to give the trans isomer.
Palladium Catalysis Enables Benzylation of α,α-Difluoroketone Enolates
Yang, Ming-Hsiu,Hunt, Jordan R.,Sharifi, Niusha,Altman, Ryan A.
supporting information, p. 9080 - 9083 (2016/07/26)
A palladium-catalyzed decarboxylative benzylation reaction of α,α-difluoroketone enolates is reported, in which the key C(α)?C(sp3) bond is generated by reductive elimination from a palladium intermediate. The transformation provides convergent access to α-benzyl-α,α-difluoroketone-based products, and should be useful for accessing biological probes.
Method for preparing alcohol through catalytic hydrogenation reduction of carboxylate
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Paragraph 0023; 0029; 0040, (2016/12/07)
The invention discloses a method for preparing alcohol through catalytic hydrogenation reduction of a carboxylate compound with 2-(diphenylphosphinoethyl)-(5,6,7,8-tetrahydroquinolyl)amine as a ruthenium complex catalyst of ligand. The catalyst has high-efficiency catalysis activity on alkyl benzoate, aromatic esters and fatty esters. The preparation method is simple and has good stability, the catalysis activity of the catalyst is high, and the dosage of the catalyst is 0.025-0.005% of the mole of a substrate. The method can be used for producing alcohols, and has the advantages of simplicity, small pollution to environment, high yield and low cost. Most of carboxylate can be hydrogenated and reduced to form alcohols by using a complex represented by formula (1) with sodium borohydride as an additive, and the conversion number TOC can reach 50000; and a cocaalyst sodium borohydride is used to substitute most of alcoholic alkalis used as a catalyst in especially used in aromatic esters with electron-withdrawing substituent, so the cost is reduced, operation is simple, and industrial production is easy.
A monolith immobilised iridium Cp catalyst for hydrogen transfer reactions under flow conditions
Rojo, Maria Victoria,Guetzoyan, Lucie,Baxendale, Ian. R.
, p. 1768 - 1777 (2015/02/19)
An immobilised iridium hydrogen transfer catalyst has been developed for use in flow based processing by incorporation of a ligand into a porous polymeric monolithic flow reactor. The monolithic construct has been used for several redox reductions demonstrating excellent recyclability, good turnover numbers and high chemical stability giving negligible metal leaching over extended periods of use.
