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Reductive Elimination (reductive + elimination)
Selected AbstractsRegiospecific Reductive Elimination from Diaryliodonium Salts,ANGEWANDTE CHEMIE, Issue 24 2010Bijia Wang Die sterische Out-of-Plane-Belastung durch einen Cyclophansubstituenten an Iod(III) destabilisiert den Übergangszustand der reduktiven Eliminierung aus Diaryliodoniumsalzen und wirkt so regiochemisch steuernd (als SECURE bezeichnet), wie Rechnungen und experimentelle Studien belegen. Dies sollte allgemein bei hochvalenten Hauptgruppen- und Übergangsmetallionen gelten. X=N3, OAc, PhO, CF3CH2O, SCN, PhS. [source] C(sp3),N Bond-Forming Reductive Elimination of Amines: Reactions of Bisphosphine-Ligated Benzylpalladium(II) Diarylamido Complexes,ANGEWANDTE CHEMIE, Issue 4 2010Seltenes Ereignis: Die bei der mechanistischen Untersuchung einer ungewöhnlichen reduktiven Eliminierung von Aminen am Benzylpalladium-Amido-Komplex 1 (Ar=Naphthyl) beobachtete Konfigurationsumkehr (siehe Schema) lässt sich mit einer Dissoziation des Amidoliganden und anschließendem nucleophilem Angriff am Benzylkohlenstoffatom erklären. Binap=2,2,-Bis(diphenylphosphanyl)-1,1,-binaphthyl, dppf=1,1,-Bis(diphenylphosphanyl)ferrocen. [source] Indium-Mediated Reductive Elimination of Halohydrins.CHEMINFORM, Issue 19 2003Sangwon Cho No abstract is available for this article. [source] ChemInform Abstract: Rates of Reductive Elimination of Substituted Nitrophenols from the (Indol-3-yl)methyl Position of Indolequinones (I),(III).CHEMINFORM, Issue 45 2001Elizabeth Swann Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] A Density Functional Study of the Hydrogenation of Ketones Catalysed by Neutral Rhodium-Diphosphane ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2006Francine Agbossou-Niedercorn Abstract The potential energy profile of RhI -catalysed hydrogenation of ketones has been computed for the simple model system [Rh{H3POCH2CH2N(H)PH3}(Cl)] using DFT calculations. The general sequence of the catalytic cycle involves coordination of the carbonyl derivative to the neutral RhI complex followed by oxidative addition of molecular hydrogen providing rhodium dihydride intermediates. The latter are converted into alkoxy hydrides by a migratory insertion reaction. Reductive elimination of the alcohol and substitution of the latter by the incoming substrate completes the catalyticcycle. Intermediates and transition states of all catalyticsteps have been located. Two isomeric derivatives bearingthe model substrate have been found for the [Rh{H3POCH2CH2N(H)PH3}(Cl)(H2CO)] complex. Eight diastereomeric pathways have been followed for the cis addition of molecular hydrogen to [Rh{H3POCH2CH2N(H)PH3}(Cl)(H2CO)] leading to eight distinct isomeric dihydride intermediates. Four dihydride complexes can be considered as the more accessible compounds. The site preference for migratory insertion and transition states discriminates the main path of the catalytic reaction. Migratory insertion to form the alkoxy hydride constitute the turn over limiting step of the process. The potential energy profile has been found to be smooth without excessive activation barriers. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] The Reductive Elimination of Methane from ansa -Hydrido(methyl)metallocenes of Molybdenum and Tungsten: Application of Hammond's Postulate to Two-State ReactionsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2005José-Luis Carreón-Macedo Abstract The energetic profile of the methane reductive elimination from a selected number of hydrido(methyl)molybdenocene and -tungstenocene derivatives has been calculated by DFT methods. The calculations were carried out for the CH2(C5H4)2M (a -M), SiH2(C5H4)2M (a -H2Si,M), and SiMe2(C5Me4)2M (a -Me2Si,M*) ansa -metallocene systems for M = Mo, W. They include the full optimization of minima [the hydrido(methyl) starting complexes, M(H)(CH3), the intermediate methane complexes, M(CH4), and the metallocene products in the singlet and triplet configurations, (3M and 1M)], transition states (for the methyl hydride reductive elimination, M,TSins, and for the hydrogen exchange, M,TSexch), and the minimum energy crossing point (M,MECP) leading from the singlet methane complexes to the corresponding triplet metallocenes. The results are compared with those previously obtained for the simpler (C5H5)2M (Cp2M) systems (J. C. Green, J. N. Harvey, and R. Poli, J. Chem. Soc., Dalton Trans.2002, 1861). The calculated energy profiles, notably the relative energies of M,TSins and M,MECP, are in agreement with available experimental observations for the a -Me2Si,M* systems. The comparison of the energies and geometries of the rate-determining M,TSins and M,MECP structures with those of the thermodynamically relevant minima for the various systems show the applicability of Hammond's postulate to two-state reactions. However, one notable exception serves to show that the principle is only quantitatively reliable when all the potential energy surfaces for the set of analogous reactions have similar shapes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Synthesis of Cyclopropanes via Organoiron Methodology: Stereoselective Preparation of Bi(cyclopropyl)sEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2007Rajesh K. Pandey Abstract Cyclopropanation of [2-(alkenyl)pentenediyl]Fe(CO)3 complexes (4) proceeds in a diastereoselective fashion to afford [2-(cyclopropyl)pentenediyl]Fe(CO)3. The relative stereochemistry of the products was established by X-ray crystallography. The diastereoselectivity is rationalized on approach of the cyclopropanation reagent on the sterically more exposed face of 4. Oxidatively induced reductive elimination afforded stereodefined bi(cyclopropyl)s. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Synthesis, characterization, and solution properties of some new organotellurium compounds based on di(cyclohexylmethyl)tellurideHETEROATOM CHEMISTRY, Issue 1 2007Ali Z. Al-Rubaie A new series of organotellurium(IV) compounds based on di(cyclohexylmethyl)telluride (1) (i.e., (C6H11CH2)2TeX2 and (C6H11CH2)2Te(R)X) was prepared by the reaction of compound 1 with halogens, N-bromosuccinimide, and alkyl halides. Phenylation of (C6H11CH2)2TeX2 with sodium tetraphenylborate gave di(cyclohexylmethyl)phenyltelluronium tetraphenylborate in good yield. Conductivity measurements in dimethylsulfoxide (DMSO) showed a considerable ionic character of these compounds and they behave as 1:1 electrolytes. 1H NMR studies in CDCl3 solution indicated that telluronium salts employed in this study are unstable toward reductive elimination. Reaction of di(cyclohexylmethyl)telluride, (C6H11CH2)2Te(CH3)I, and (C6H11CH2)2Te(PhCH2)Br with HgX2 (X = Cl or Br) afforded 1:1 complexes. All compounds were characterized by elemental analyses and spectroscopic data. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:93,99, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20240 [source] Catalytic Dicyanative 5- exo- and 6- endo -Cyclization Triggered by Cyanopalladation of AlkynesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 5 2010Shigeru Arai Abstract A stereoselective dicyanative 5- exo- and 6- endo -cyclization using various enynes has been investigated. The mode of cyclization is critically controlled by the structure of the substrates. For example, N -allyl derivatives prefer 5- exo -cyclization, while methacryloyl amides are transformed to the corresponding lactams with tetra -substituted carbons at the alpha-position via 6- endo -cyclization. Both reactions include syn -cyanopalladation to carboncarbon triple bonds in the initial step, and sequential cyclization followed by reductive elimination in one operation enables the construction of the highly functionalized nitrogen heterocycles. The scope of suitable substrates and a proposed mechanism are also described. [source] Mechanism of the Nucleophilic Substitution of Acyl Electrophiles using Lithium OrganocupratesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7-8 2008Naohiko Yoshikai Abstract The mechanism of nucleophilic substitution reaction at an sp2 carbon center of a thioester or an acid chloride with a lithium organocuprate reagent has been investigated. Density functional calculations indicated that the thioester undergoes oxidative addition of the CS bond to the copper(I) atom through a three-centered transition state to afford an organocopper(III) intermediate, which gives the product through reductive elimination of the alkyl and the acyl groups. On the other hand, the acid chloride loses a chloride anion very easily when it interacts with the cuprate, because the chloride anion is captured by a lithium(I) cation rather than a copper(I) atom. 13C kinetic isotope effect (KIE) experiments showed excellent agreement with computational predictions for the thioester reaction, but suggested that the nucleophilic displacement transition state of the acid chloride occurs much more advanced than the calculations predict. [source] Applications of deuterium isotope effects for probing aspects of reactions involving oxidative addition and reductive elimination of H,H and C,H bonds,JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 11-12 2007Gerard Parkin Abstract The various types of deuterium isotope effects that are observed for reactions involving oxidative addition and reductive elimination reactions of H,H and C,H bonds with a transition metal center are reviewed. Copyright © 2007 John Wiley & Sons, Ltd. [source] Detection of platinum dihydride bisphosphine complexes and studies of their reactivity through para -hydrogen-enhanced NMR methodsMAGNETIC RESONANCE IN CHEMISTRY, Issue S1 2008Cyril Godard Abstract In-situ NMR studies on the reactions of Pt{CH2 = CHSi(Me)2}2O)(PCy3) with phosphines, HSiEt3 and - hydrogen or Pt(L)(L,)(Me)2 alone enable the detection of cis -Pt(L)(L,)(H)2 [L = PCy3 and L, = PCy2H, PPh3 or PCy3] which then undergo hydride site interchange and H2 reductive elimination on the NMR timescale. Copyright © 2008 John Wiley & Sons, Ltd. [source] ChemInform Abstract: Expeditious Synthesis of Highly Substituted Indolizinones via a Palladium-Catalyzed Domino Sequence.CHEMINFORM, Issue 43 2010Ikyon Kim Abstract Aminopalladation, reductive elimination and 1,2-shift allow the synthesis of a broad spectrum of indolizinones as an interesting pharmacophore from propargylic alcohols (I) and aryl iodides. [source] Cobalt-Mediated Linear 2:1 Co-oligomerization of Alkynes with Enol Ethers to Give 1-Alkoxy-1,3,5-Trienes: A Missing Mode of ReactivityCHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2010David Leb, uf Dr. Abstract A variety of 1,6-heptadiynes and certain borylalkynes co-oligomerize with enol ethers in the presence of [CpCo(C2H4)2] (Cp=cyclopentadienyl) to furnish the hitherto elusive acyclic 2:1 products, 1,3,5-trien-1-ol ethers, in preference to or in competition with the alternative pathway that leads to the standard [2+2+2] cycloadducts, 5-alkoxy-1,3-cyclohexadienes. Minor variations, such as lengthening the diyne tether, cause reversion to the standard mechanism. The trienes, including synthetically potent borylated derivatives, are generated with excellent levels of chemo-, regio-, and diastereoselectivity, and are obtained directly by decomplexation of the crude mixtures during chromatography. The cyclohexadienes are isolated as the corresponding dehydroalkoxylated arenes. In one example, even ethene functions as a linear cotrimerization partner. The alkoxytrienes are thermally labile with respect to 6,-electrocyclization,elimination to give the same arenes that are the products of cycloaddition. The latter, regardless of the mechanism of their formation, can be viewed as the result of a formal [2+2+2] cyclization of the starting alkynes with acetylene. One-pot conditions for the exclusive formation of arenes are developed. DFT computations indicate that cyclohexadiene and triene formation share a common intermediate, a cobaltacycloheptadiene, from which reductive elimination and ,-hydride elimination compete. [source] Mapping the Transformation [{RuII(CO)3Cl2}2],[RuI2(CO)4]2+: Implications in Binuclear Water,Gas Shift ChemistryCHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2010Moumita Majumdar Abstract The complete sequence of reactions in the base-promoted reduction of [{RuII(CO)3Cl2}2] to [RuI2(CO)4]2+ has been unraveled. Several ,-OH, ,:,2 -CO2H-bridged diruthenium(II) complexes have been synthesized; they are the direct results of the nucleophilic activation of metal-coordinated carbonyls by hydroxides. The isolated compounds are [Ru2(CO)4(,:,2 - C,O -CO2H)2(,-OH)(NPF -Am)2][PF6] (1; NPF -Am=2-amino-5,7-trifluoromethyl-1,8-naphthyridine) and [Ru2(CO)4(,:,2 - C,O -CO2H)(,-OH)(NP-Me2)2][BF4]2 (2), secured by the applications of naphthyridine derivatives. In the absence of any capping ligand, a tetranuclear complex [Ru4(CO)8(H2O)2(,3 -OH)2(,:,2 - C,O -CO2H)4][CF3SO3]2 (3) is isolated. The bridging hydroxido ligand in 1 is readily replaced by a ,-donor chlorido ligand, which results in [Ru2(CO)4(,:,2 - C,O -CO2H)2(,-Cl)(NP-PhOMe)2][BF4] (4). The production of [Ru2(CO)4]2+ has been attributed to the thermally induced decarboxylation of a bis(hydroxycarbonyl),diruthenium(II) complex to a dihydrido,diruthenium(II) species, followed by dinuclear reductive elimination of molecular hydrogen with the concomitant formation of the RuIRuI single bond. This work was originally instituted to find a reliable synthetic protocol for the [Ru2(CO)4(CH3CN)6]2+ precursor. It is herein prescribed that at least four equivalents of base, complete removal of chlorido ligands by TlI salts, and heating at reflux in acetonitrile for a period of four hours are the conditions for the optimal conversion. Premature quenching of the reaction resulted in the isolation of a trinuclear RuI2RuII complex [{Ru(NP-Am)2(CO)}{Ru2(NP-Am)2(CO)2(,-CO)2}(,3:,3 - C,O,O, -CO2)][BF4]2 (6). These unprecedented diruthenium compounds are the dinuclear congeners of the water,gas shift (WGS) intermediates. The possibility of a dinuclear pathway eliminates the inherent contradiction of pH demands in the WGS catalytic cycle in an alkaline medium. A cooperative binuclear elimination could be a viable route for hydrogen production in WGS chemistry. [source] Two Distinct Mechanisms of Alkyne Insertion into the Metal,Sulfur Bond: Combined Experimental and Theoretical Study and Application in CatalysisCHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2010Valentine Abstract The present study reports the evidence for the multiple carbon,carbon bond insertion into the metal,heteroatom bond via a five-coordinate metal complex. Detailed analysis of the model catalytic reaction of the carbon,sulfur (CS) bond formation unveiled the mechanism of metal-mediated alkyne insertion: a new pathway of CS bond formation without preliminary ligand dissociation was revealed based on experimental and theoretical investigations. According to this pathway alkyne insertion into the metal,sulfur bond led to the formation of intermediate metal complex capable of direct CS reductive elimination. In contrast, an intermediate metal complex formed through alkyne insertion through the traditional pathway involving preliminary ligand dissociation suffered from "improper" geometry configuration, which may block the whole catalytic cycle. A new catalytic system was developed to solve the problem of stereoselective SS bond addition to internal alkynes and a cost-efficient Ni-catalyzed synthetic procedure is reported to furnish formation of target vinyl sulfides with high yields (up to 99,%) and excellent Z/E selectivity (>99:1). [source] Metal-Mediated Formation of Carbon,Halogen BondsCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2008Arkadi Vigalok Prof. Dr. Abstract Organic halides represent basic starting materials for numerous metal-catalyzed organic transformations. Generally, the carbon,halogen is broken in the first step, that is, an oxidative addition reaction, of the catalytic cycle. On the other hand, very little is known about the reverse reaction, carbon,halogen reductive elimination from a transition-metal center. In this Concept article, we describe the examples of C(sp3)halide and C(sp2)halide reductive-elimination reactions which demonstrate that this type of reactivity can be quite common in organometallic chemistry. Although the thermodynamic driving force for the formation of carbon,halogen bonds is relatively small, the kinetic barrier for these reactions can also be low. Thus, Chalide reductive elimination can compete favorably with the more established organic transformations, such as CC reductive elimination. [source] Mechanism of Reppe's Nickel-Catalyzed Ethyne Tetramerization to Cyclooctatetraene: A DFT StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2004Bernd F. Straub Dr. Abstract In this B3,LYP model study, homoleptic nickel(0) ethyne complexes have been predicted as the catalyst resting state for the title reaction. Ethyne ligand coupling of Ni(C2H2)3 yields monoethyne nickelacyclopentadiene in the rate-determining step. Ethyne coordination is followed by insertion of an ethyne ligand into the NiC , bond. A highly strained monoethyne trans -nickelacycloheptatriene is formed. This trans intermediate is unable to reductively eliminate benzene without prior isomerization to a cis -structure. Instead, it rapidly collapses to a nickelacyclononatetraene. Ethyne coordination induces reductive elimination to the cyclooctatetraene complex Ni(,2 -C2H2)(,2 -C8H8), followed by facile ligand exchange. Other ethyne coupling pathways have been computed to be less favored. The cyclooctatetraene ligand binds significantly weaker to nickel(0) than ethyne, both for mononuclear, and for dinuclear species. For this reason, CC bond formation steps at Ni2(,-cot) fragments have been predicted to feature prohibitively high overall reaction barriers. In dieser B3,LYP-Studie werden homoleptische Nickel(0)-Ethinkomplexe als Katalysatorruhezustand von Reppes Cyclooctatetraensynthese vorhergesagt. Kupplung zweier Ethinliganden in Ni(C2H2)3 ergibt Monoethin-Nickelacyclopentadien im geschwindigkeitsbestimmenden Schritt. Der Koordination von Ethin folgt die Insertion eines Ethinliganden in die NiC ,-Bindung. Ein hoch gespanntes Monoethin- trans -Nickelacycloheptatrien wird gebildet. Dieses trans -Intermediat ist nicht in der Lage, Benzol reduktiv zu eliminieren, ohne vorher in eine cis -Struktur zu isomerisieren. Stattdessen kollabiert es schnell zu Nickelacyclononatetraen. Koordination von Ethin induziert eine barrierefreie reduktive Eliminierung zum Cyclooctatetraen Komplex Ni(,2 -C2H2)(,2 -C8H8), gefolgt von einem einfach verlaufenden Ligandenaustausch. Andere Ethinkupplungspfade wurden als weniger begünstigt berechnet. Der COT-Ligand bindet sowohl für mononukleare als auch für dinukleare Spezies deutlich schwächer an Nickel(0) als Ethin. Aus diesem Grund werden für CC-Bindungsbildungsschritte am Ni2(,-cot)-Fragment prohibitiv hohe freie Aktivierungsenthalpien vorhergesagt. [source] Mechanism of Remote Conjugate Addition of Lithium Organocuprates to Polyconjugated Carbonyl CompoundsCHEMISTRY - AN ASIAN JOURNAL, Issue 3 2006Naohiko Yoshikai Abstract Regioselective reaction of a lithium organocuprate (R2CuLi) and a polyconjugated carbonyl compound affords a remote-conjugate-addition product. This reaction proceeds particularly cleanly when the conjugation is terminated by a CC triple bond. The reaction pathways and the origin of the regioselectivity of this class of transformations are explored with the aid of density functional calculations. The outline of the reaction pathway is as follows. An initially formed ,-cuprio(III) enolate intermediate undergoes smooth copper migration along the conjugated system. This process takes place faster than reductive elimination of intermediary ,/,-allylcopper(III) species, since the latter reaction disrupts the conjugation in the substrate and hence is not preferred. The copper migration to the acetylenic terminal affords a ,/,-allenylcopper(III) intermediate, which undergoes facile and selective CC bond forming reductive elimination at the terminal carbon atom. The present mechanistic framework shows good agreement with some pertinent experimental data, including 13C,NMR chemical shifts and kinetic isotope effects. [source] | ||||||||||||||||||||||