- Half-Sandwich Guanidinate-Osmium(II) Complexes: Synthesis and Application in the Selective Dehydration of Aldoximes
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The novel guanidinate-osmium(II) complexes [OsCl{κ2-(N,N′)-C(NR)(NiPr)NHiPr}(η6-p-cymene)] [R = Ph (3a), 4-C6H4F (3b), 4-C6H4Cl (3c), 4-C6H4CF3 (3d), 3-C6H4CF3 (3e), 3,5-C6H3(CF3)2 (3f), 4-C6H4CN (3g), 4-C6H4Me (3h), 3-C6H4Me (3i), 2-C6H4Me (3j), 4-C6H4tBu (3k), 2,6-C6H3iPr2 (3l), 2,4,6-C6H2Me3 (3m)] have been synthesized in high yields (70-88 %) by treatment of THF solutions of the dimeric precursor [{OsCl(μ-Cl)(η6-p-cymene)}2] (1) with 4 equivalents of the corresponding guanidine (iPrHN)2C=NR (2a-m) at room temperature. The easily separable guanidinium chloride salts [(iPrHN)2C(NHR)]Cl (4a-m) were also formed in these reactions. The structures of 3a, 3d, and 3h were unequivocally confirmed by X-ray diffraction methods. Complexes 3a-m proved to be active in the catalytic dehydration of aldoximes. The best results were obtained with [OsCl{κ2-(N,N′)-C(N-4-C6H4CF3)(NiPr)NHiPr}(η6-p-cymene)] (3d; 5 mol-%), which, in acetonitrile at 80C, was able to convert selectively a large variety of aromatic, heteroaromatic, α,β-unsaturated, and aliphatic aldoximes into the corresponding nitriles in high yields and short reaction times. Novel osmium(II)-guanidinate complexes of general composition [OsCl{κ2-(N,N′)-C(NR)(NiPr)NHiPr}(η6-p-cymene)] (R = Ar) have been synthesized and successfully employed as catalysts for the selective conversion of aldoximes into nitriles.
- Francos, Javier,González-Liste, Pedro J.,Menéndez-Rodríguez, Lucía,Crochet, Pascale,Cadierno, Victorio,Borge, Javier,Anti?olo, Antonio,Fernández-Galán, Rafael,Carrillo-Hermosilla, Fernando
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p. 393 - 402
(2016/02/03)
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- Palladium(II) complexes with a phosphino-oxime ligand: Synthesis, structure and applications to the catalytic rearrangement and dehydration of aldoximes
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The treatment of [PdCl2(COD)] (COD = 1,5-cyclooctadiene) with 1 and 2 equivalents of 2-(diphenylphosphino)benzaldehyde oxime in dichloromethane at room temperature led to the selective formation of [PdCl2{κ2-(P,N)-2-Ph2PC6H4CHNOH}] (1) and [Pd{κ2-(P,N)-2-Ph2PC6H4CHNOH}2][Cl]2 (2), respectively, which represent the first examples of Pd(II) complexes containing a phosphino-oxime ligand. These compounds, whose structures were fully confirmed by X-ray diffraction methods, were active in the catalytic rearrangement of aldoximes. In particular, using 5 mol% complex 1, a large variety of aldoximes could be cleanly converted into the corresponding primary amides at 100 °C, employing water as solvent and without the assistance of any cocatalyst. Palladium nanoparticles are the active species in the rearrangement process. In addition, when the same reactions were performed employing acetonitrile as solvent, selective dehydration of the aldoximes to form the respective nitriles was observed. For comparative purposes, the catalytic behaviour of an oxime-derived palladacyclic complex has also been briefly evaluated.
- Menéndez-Rodríguez, Lucía,Tomás-Mendivil, Eder,Francos, Javier,Nájera, Carmen,Crochet, Pascale,Cadierno, Victorio
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p. 3754 - 3761
(2015/07/01)
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- Cyclic aromatic analogues of the hendrickson reagent; NMR studies and electrophilic properties
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Two novel cyclic aromatic analogues of the Hendrickson POP reagent, 1,1,3,3-tetraphenyl-1,3-dihydro-2,1,3-benzoxadiphosphole-1,3-diium bis(trifluoromethanesulfinate) and bis(trifluoromethanesulfonate), have been readily prepared by the treatment of 1,2-bis(diphenylphosphino)benzene or 1,2-bis(diphenylphosphoryl)benzene, respectively, with trifluoromethanesulfonic anhydride in dichloromethane. 31P and 19F NMR studies indicated that while the latter complex is formed as the sole product, the former species was shown to be the predominant component in equilibrium with 1-(diphenylphosphino)-2-[diphenyl(trifluoromethylsulfonyloxy)phosphonio]benzene trifluoromethanesulfinate and 1,2-bis[diphenyl(trifluoromethylsulfonyloxy) phosphonio]benzene bis(trifluoromethanesulfinate). The dehydrating POP systems were exploited in the conversion of aldoximes into nitriles. The dehydration occurred rapidly at room temperature and produced high yields with a variety of alkyl- and arylaldoximes, tolerating a wide range of substrates and functional groups. Georg Thieme Verlag Stuttgart New York.
- Moussa, Ziad
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experimental part
p. 460 - 468
(2012/03/11)
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- Nucleophilic fluorination reactions starting from aqueous fluoride ion solutions
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The sulfonium borane 2+ reacts with fluoride anions in MeOH/H2O mixtures to afford the zwitterionic fluoroborate 2-F as an easily isolable nonhygroscopic solid. In dry acetonitrile, 2-F reacts with PhS- to afford the anionic fluoroborate 1-F-. The latter is very labile and acts as a nucleophilic fluorination reagent toward a variety of substrates including alkylhalides and electron-deficient aromatic compounds. This approach may become broadly applicable to nucleophilic fluorination procedures that involve wet fluoride sources.
- Zhao, Haiyan,Gabbai, Francois P.
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supporting information; experimental part
p. 1444 - 1446
(2011/05/08)
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- NMR Studies and electrophilic properties of triphenylphosphine-trifluoromethanesulfonic anhydride; a remarkable dehydrating reagent system for the conversion of aldoximes into nitriles
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NMR Studies on the reaction of triphenylphosphine with various amounts of triflic anhydride at 0 °C is described. The reagent structure resulting from mixing 1.3 equiv of Ph3P with Tf2O (1.0 mmol) has been established as an equilibrium mixture consisting mainly of triphenyl(trifluoromethylsulfonyloxy)phosphonium trifluoromethanesulfinate and the corresponding bis(triphenyl)oxodiphosphonium trifluoromethanesulfinate dimer. The electrophilic properties of the system have been exploited in the development of a mild method for converting aldoximes into nitriles. The dehydration occurs at 0 °C under very mild conditions by initial activation of the oxime oxygen, followed by treatment with a base and subsequent elimination of triphenylphosphine oxide. The substrate scope and functional group tolerance of this useful method are explored.
- Moussa, Ziad,Ahmed, Saleh A.,ElDouhaibi, Ahmad S.,Al-Raqa, Shaya Y.
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experimental part
p. 1826 - 1831
(2010/09/07)
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- METHOD FOR PRODUCING SUBSTITUTED ORGANIC COMPOUNDS AND USE OF CATALYSTS FOR SUBSTITUTION REACTIONS
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The invention relates to a method for exchanging substituents in organic compounds, for example, chlorine for fluorine. The method involves the use of a catalyst of formulas (IVa), (IVb) or (IVc), wherein: radicals R2 to R17, independent of one another, represent hydrogen, aliphatic, cycloaliphatic, aromatic or araliphatic groups; Aq- represents a q-valent anion, and q is an integer ranging from 1 to 3.
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- Unexpected side products in the tetramethylammonium fluoride-dimethylsulphoxide system
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Reactions of chloro- and nitro-aromatics with low water content solutions of TMAF in DMSO can lead to complex product mixtures resulting from activation of DMSO by fluoride and the formation of DMSO-derived products. Also, the system has been shown to give hydrolysis products in addition to the well-known ethers and phenols, with carboxylic acids and benzamides being formed from the attempted fluorodenitration of substituted benzonitriles.
- Adams, Dave J.,Clark, James H.,McFarland, Heather,Nightingale, David J.
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- The effect of basicity on fluorodenitration reactions using tetramethylammonium salts
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The fluorodenitration of several nitroaromatics with tetramethylammonium salts has been found to be dependent on the basicity of the fluorinating species. Tetramethylammonium fluoride is highly basic and is capable of inducing H-D exchange in 1,3-dinitrobenzene, as well as deprotonating N,N- dimethylacetamide. Reaction of the fluoride with phthalic anhydride forms the bifluoride in situ. Tetramethylammonium bifluoride gives higher yields of the required fluoroaromatic, but slower reaction rates than the corresponding fluoride.
- Adams, Dave J.,Clark, James H.,Nightingale, David J.
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p. 7725 - 7738
(2007/10/03)
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- Tetramethylammonium hydrogendifluoride: A convenient source of nucleophilic fluoride
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Tetramethylammonium hydrogendifluoride (TMAHF2) acts as an effective fluoride source for the selective fluorination in high yields of various chloro and nitroaromatics via halogen exchange (halex) and fluorodenitration.
- Adams, David J.,Clark, James H.,Nightingale, David J.
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p. 4295 - 4301
(2007/10/03)
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- Reaction of tetramethylammonium fluoride with trifluoromethyltrimethylsilane
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Tetramethylammonium fluoride reacts with either triluoromethyltrimethylsilane or trimethylsilylacetonitrile in acetonitrile to form a pentacoordinate silicon species, which can act as a source of either fluoride or cyanomethyl carbanion, depending on substrate.
- Adams, Dave J.,Clark, James H.,Hansen, Liv B.,Sanders, Victoria C.,Tavener, Stewart J.
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p. 123 - 125
(2007/10/03)
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- Process for preparing organic fluorides
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A method for the preparation of organic fluorides which comprises reacting a quaternary phosphonium fluoride or bifluoride with an organic substrate having at least one atom or group capable of being replaced by a fluorine atom.
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- THE SYNTHESIS OF ORGANOFLUORINE COMPOUNDS USING POTASSIUM FLUORIDE-TETRAPHENYLPHOSPHONIUM BROMIDE SYSTEMS.
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The reactivity of potassium fluoride in nucleophilic fluorine transfer reactions can appreciably enhanced by the presence of tetraphenyl phosphonium bromide.Rate accelerations are especially large in non dipolar aprotic solvents.
- Clark, James H.,Macquarrie, Duncan J.
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p. 111 - 114
(2007/10/02)
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- SUBSTRATE DEPENDENT SOLVENT EFFECTS IN NUCLEOPHILIC FLUORINE TRANSFER REACTIONS
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The rate of fluorination of organic substrates by potassium fluoride in aprotic solvents is subject to substrate dependent solvent effects.
- Clark, J. H.,MacQuarrie, D.
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p. 591 - 596
(2007/10/02)
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- FLUORODENITRATIONS USING TETRABUTYLAMMONIUM FLUORIDE
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Fluoroaromatics are prepared in good yield under mild conditions using the tetrabutylammonium fluoride promoted fluorodenitration of nitroaromatics.
- Clark, James H.,Smith, David K.
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p. 2233 - 2236
(2007/10/02)
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- THE FLUORINATION OF ORGANIC SUBSTRATES WITH TETRAPHENYLPHOSPHONIUM HYDROGENDIFLUORIDE
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Tetraphenylphosphonium hydrogendifluoride acts as a powerful source of F- in various reactions with organic substrates to give fluorine containing products.
- Brown, S. J.,Clark, J. H.
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p. 251 - 258
(2007/10/02)
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