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John F. Hartwig - One of the best experts on this subject based on the ideXlab platform.
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carbon sp3 nitrogen bond forming Reductive Elimination from phosphine ligated alkylpalladium ii amide complexes a dft study
Tetrahedron, 2019Co-Authors: Quan Jiang, John F. Hartwig, Matthew D. Peacock, Thomas R CundariAbstract:Abstract DFT methods were employed to investigate C(sp3)-N bond-formation via Reductive Elimination from alkylpalladium(II) amide complexes. The hemi-lability of an ortho-methoxy substituent is computed to have minimal impact on Reductive Elimination barriers. In general, for both anilide and phosphine substituents, their steric impact is more substantial than electronic/Hammett factors. β-Hydrogen Elimination is competitive with Reductive Elimination while β-methyl Elimination is much less favorable. For phosphine-ligated Pd(II) amide complexes, the solvent impact on Reductive Elimination free energy barriers is small, and overall the substituent effects on either the phosphine or anilide ligand are subtle.
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Reductive Elimination from phosphine ligated alkylpalladium ii amido complexes to form sp3 carbon nitrogen bonds
Journal of the American Chemical Society, 2018Co-Authors: Matthew D. Peacock, Thomas R Cundari, Patrick S Hanley, Quan Jiang, John F. HartwigAbstract:We report the formation of phosphine-ligated alkylpalladium(II) amido complexes that undergo Reductive Elimination to form alkyl-nitrogen bonds and a combined experimental and computational investigation of the factors controlling the rates of these reactions. The free-energy barriers to Reductive Elimination from t-Bu3P-ligated complexes were significantly lower (ca. 3 kcal/mol) than those previously reported from NHC-ligated complexes. The rates of reactions from complexes containing a series of electronically and sterically varied anilido ligands showed that the Reductive Elimination is slower from complexes of less electron-rich or more sterically hindered anilido ligands than from those containing more electron-rich and less hindered anilido ligands. Reductive Elimination of alkylamines also occurred from complexes bearing bidentate P,O ligands. The rates of reactions of these four-coordinate complexes were slower than those for reactions of the three-coordinate, t-Bu3P-ligated complexes. The calcula...
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Reductive Elimination from Phosphine-Ligated Alkylpalladium(II) Amido Complexes To Form sp3 Carbon–Nitrogen Bonds
2018Co-Authors: Matthew D. Peacock, Thomas R Cundari, Patrick S Hanley, Quan Jiang, John F. HartwigAbstract:We report the formation of phosphine-ligated alkylpalladium(II) amido complexes that undergo Reductive Elimination to form alkyl-nitrogen bonds and a combined experimental and computational investigation of the factors controlling the rates of these reactions. The free-energy barriers to Reductive Elimination from t-Bu3P-ligated complexes were significantly lower (ca. 3 kcal/mol) than those previously reported from NHC-ligated complexes. The rates of reactions from complexes containing a series of electronically and sterically varied anilido ligands showed that the Reductive Elimination is slower from complexes of less electron-rich or more sterically hindered anilido ligands than from those containing more electron-rich and less hindered anilido ligands. Reductive Elimination of alkylamines also occurred from complexes bearing bidentate P,O ligands. The rates of reactions of these four-coordinate complexes were slower than those for reactions of the three-coordinate, t-Bu3P-ligated complexes. The calculated pathway for Reductive Elimination from rigid, 2-methoxyarylphosphine-ligated complexes does not involve initial dissociation of the oxygen. Instead, Reductive Elimination is calculated to occur directly from the four-coordinate complex in concert with a lengthening of the Pd–O bond. To investigate this effect experimentally, a four-coordinate Pd(II) anilido complex containing a flexible, aliphatic linker between the P and O atoms was synthesized. Reductive Elimination from this complex was faster than that from the analogous complex containing the more rigid, aryl linker. The flexible linker enables full dissociation of the ether ligand during Reductive Elimination, leading to the faster reaction of this complex
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Reductive Elimination of alkylamines from low valent alkylpalladium ii amido complexes
Journal of the American Chemical Society, 2012Co-Authors: Patrick S Hanley, Seth L Marquard, Thomas R Cundari, John F. HartwigAbstract:A series of three-coordinate norbornylpalladium amido complexes ligated by bulky N-heterocyclic carbene (NHC) ligands were prepared that undergo Reductive Eliminations to form the alkyl–nitrogen bond of alkylamine products. The rates of Reductive Elimination reveal that complexes containing more-electron-donating amido groups react faster than those with less-electron-donating amido groups, and complexes containing more-sterically bulky amido groups undergo Reductive Elimination more slowly than complexes containing less-sterically bulky amido groups. Complexes ligated by more-electron-donating ancillary NHC ligands undergo Reductive Elimination faster than complexes ligated by less-electron-donating NHC ligands. In contrast to the Reductive Elimination of benzylamines from bisphosphine-ligated palladium amides, these reactions occur with retention of configuration at the alkyl group, indicating that these Reductive Eliminations proceed by a concerted pathway. The experimentally determined free energy bar...
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Reductive Elimination from arylpalladium cyanide complexes.
Journal of the American Chemical Society, 2012Co-Authors: Jessica L. Klinkenberg, John F. HartwigAbstract:We report the isolation and characterization of arylpalladium cyanide complexes that undergo Reductive Elimination to form arylnitriles. The rates of Reductive Elimination from a series of arylpalladium cyanide complexes reveal that the electronic effects on the Reductive Elimination from arylpalladium cyanide complexes are distinct from those on Reductive Reductive Eliminations from arylpalladium alkoxo, amido, thiolate, and enolate complexes. Arylpalladium cyanide complexes containing aryl ligands with electron-donating substituents undergo Reductive Elimination of aromatic nitriles faster than complexes containing aryl ligands with electron-withdrawing substituents. In addition, the transition state for the Reductive Elimination of the aromatic nitrile is much different from that for Reductive Eliminations that occur from most other arylpalladium complexes. Computational studies indicate that the Reductive Elimination of an arylnitrile from Pd(II) occurs through a transition state more closely related ...
Karen I Goldberg - One of the best experts on this subject based on the ideXlab platform.
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Reductive Elimination and dissociative β hydride abstraction from pt iv hydroxide and methoxide complexes
Organometallics, 2009Co-Authors: Nicole A Smythe, Kyle A Grice, Scott B Williams, Karen I GoldbergAbstract:The platinum(IV) hydroxide and methoxide complexes fac-(dppbz)PtMe3(OR) (dppbz = o-bis(diphenylphosphino)benzene; R = H (1), CH3 (2)) have been prepared and characterized. Thermolysis of hydroxide 1 produces (dppbz)PtMe2 (3) and methanol in a rare example of directly observed sp3 carbon−oxygen Reductive Elimination from a metal center to form an alcohol. Competitive carbon−carbon Reductive Elimination to form (dppbz)PtMe(OH) (5) and ethane also occurs. In contrast, the major reaction observed upon thermolysis of the methoxide analog 2 is neither carbon−oxygen nor carbon−carbon Reductive Elimination. Instead, products expected from formal β-hydride Elimination followed by carbon−hydrogen Reductive Elimination are detected. Mechanistic studies suggest the operation of an alternative mechanism to that most commonly accepted for this fundamental reaction; a dissociative β-hydride abstraction pathway is proposed.
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Reductive Elimination of ethane from five coordinate platinum iv alkyl complexes
Inorganic Chemistry, 2007Co-Authors: Avery T Luedtke, Karen I GoldbergAbstract:Five-coordinate platinum(IV) alkyl complexes bearing sterically non-demanding pyridylpyrrolide ligands, (LX)PtMe3 [LX = 3,5-di-tert-butyl-2-(2-pyridyl)pyrrolide (3a) and 3,5-diphenyl-2-(2-pyridyl)pyrrolide (3b)] have been prepared. An X-ray structure of 3a estab-lishes that it is a five-coordinate PtIV complex with a square-pyramidal geometry. Thermolysis of 3a or 3b in C6D6 with ethylene results in Reductive Elimination of ethane (C2H6) and methane (CH4 and CH3D) and the formation of cyclometalated platinum(II) ethylene complexes 4a or 4b, respectively. Results of kinetic investigations of the reaction of 3b are consistent with a mechanism of direct C−C Reductive Elimination from the five-coordinate PtIV compound. Thermolysis of 3a in C6D6 with no ethylene present forms a novel dinuclear complex (5-d6).
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alkyl carbon nitrogen Reductive Elimination from platinum iv sulfonamide complexes
Journal of the American Chemical Society, 2007Co-Authors: Andrew V Pawlikowski, And April D Getty, Karen I GoldbergAbstract:Platinum(IV) complexes containing monodentate sulfonamide ligands, fac-(dppbz)PtMe3(NHSO2R) (dppbz = o-bis(diphenylphosphino)benzene; R = p-C6H4(CH2)3CH3 (1a), p-C6H4CH3 (1b), CH3 (1c)), have been synthesized and characterized, and their thermal reactivity has been explored. Compounds 1a−c undergo competitive C−N and C−C Reductive Elimination upon thermolysis to form N-methylsulfonamides and ethane, respectively. Selectivity for either C−N or C−C bond formation can be achieved by altering the reaction conditions. Good yields of the C−N-coupled products were observed when the thermolyses of 1a−c were conducted in benzene-d6. In contrast, exclusive C−C Reductive Elimination occurred upon themolysis of 1a,b in nitrobenzene-d5. When the thermolyses of 1a were performed in the presence of sulfonamide anion NHSO2R- in benzene-d6, ethane Elimination was completely inhibited and C−N Reductive Elimination products were formed in high yield. Mechanistic studies support a two-step reaction pathway involving initial ...
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Studies of Reductive Elimination reactions to form carbon-oxygen bonds from Pt(IV) complexes.
Journal of the American Chemical Society, 2001Co-Authors: B. Scott Williams And, Karen I GoldbergAbstract:The platinum(IV) complexes fac-L2PtMe3(OR) (L2 = bis(diphenylphosphino)ethane, o-bis(diphenylphosphino)benzene, R = carboxyl, aryl; L = PMe3, R = aryl) undergo Reductive Elimination reactions to form carbon−oxygen bonds and/or carbon−carbon bonds. The carbon−oxygen Reductive Elimination reaction produces either methyl esters or methyl aryl ethers (anisoles) and L2PtMe2, while the carbon−carbon Reductive Elimination reaction affords ethane and L2PtMe(OR). Choice of reaction conditions allows the selection of either type of coupling over the other. A detailed mechanistic study of the Reductive Elimination reactions supports dissociation of the OR- ligand as the initial step for the C−O bond formation reaction. This is followed by a nucleophilic attack of OR- upon a methyl group bound to the Pt(IV) cation to produce the products MeOR and L2PtMe2. C−C Reductive Elimination proceeds from L2PtMe3(OR) by initial L (L = PMe3) or OR- (L2 = dppe, dppbz) dissociation, followed by C−C coupling from the resulting five...
Arkadi Vigalok - One of the best experts on this subject based on the ideXlab platform.
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Selective Aryl–Fluoride Reductive Elimination from a Platinum(IV) Complex
Angewandte Chemie (International ed. in English), 2015Co-Authors: Ina S. Dubinsky-davidchik, Israel Goldberg, Arkadi Vigalok, Andrei N. VedernikovAbstract:A difluoro(mesityl)platinum(IV) complex underwent highly selective Reductive Elimination of 2-fluoromesitylene upon heating in toluene. Kinetic analysis and DFT calculations suggest that the CF coupling involves a five-coordinate PtIV transient intermediate resulting from the rate-limiting dissociation of the pyridine ligand.
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Electrophilic Halogenation-Reductive Elimination Chemistry of Organopalladium and -Platinum Complexes
ChemInform, 2015Co-Authors: Arkadi VigalokAbstract:ConspectusTransition metal-catalyzed organic transformations often reveal competing reaction pathways. Determining the factors that control the selectivity of such reactions is of extreme importance for the design of reliable synthetic protocols. Herein, we present the account of our studies over the past decade aimed at understanding the selectivity of Reductive Elimination chemistry of organotransition metal complexes under electrophilic halogenation conditions. Much of our effort has focused on finding the conditions for selective formation of carbon (aryl)–halogen bonds in the presence of competing C–C Reductive Elimination alternatives. In most cases, the latter was the thermodynamically preferred pathway; however, we found that the reactions could be diverted toward the formation of aryl–iodine and aryl–bromine bonds under kinetic conditions. Of particular importance was to maintain the complex geometry that prohibits C–C Elimination while allowing for the Elimination of carbon–halogen bonds. This w...
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Electrophilic Halogenation–Reductive Elimination Chemistry of Organopalladium and -Platinum Complexes
Accounts of chemical research, 2015Co-Authors: Arkadi VigalokAbstract:ConspectusTransition metal-catalyzed organic transformations often reveal competing reaction pathways. Determining the factors that control the selectivity of such reactions is of extreme importance for the design of reliable synthetic protocols. Herein, we present the account of our studies over the past decade aimed at understanding the selectivity of Reductive Elimination chemistry of organotransition metal complexes under electrophilic halogenation conditions. Much of our effort has focused on finding the conditions for selective formation of carbon (aryl)–halogen bonds in the presence of competing C–C Reductive Elimination alternatives. In most cases, the latter was the thermodynamically preferred pathway; however, we found that the reactions could be diverted toward the formation of aryl–iodine and aryl–bromine bonds under kinetic conditions. Of particular importance was to maintain the complex geometry that prohibits C–C Elimination while allowing for the Elimination of carbon–halogen bonds. This w...
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Aryl-halide versus aryl-aryl Reductive Elimination in Pt(IV)-phosphine complexes.
Journal of the American Chemical Society, 2006Co-Authors: Anette Yahav-levi, Israel Goldberg, Arkadi VigalokAbstract:Upon the addition of Br2 to complexes (P−P)Pt(Ar)2, two different products were observed, depending on the bite angle of the bidentate phosphine ligand: a Pt(II) aryl bromide complex, the product of C−Br Reductive Elimination, and Pt(IV) oxidative addition complex. At high temperatures, the latter exclusively gave the product of the C−C Reductive Elimination.
F. Dean Toste - One of the best experts on this subject based on the ideXlab platform.
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Halide-Dependent Mechanisms of Reductive Elimination from Gold(III).
Journal of the American Chemical Society, 2015Co-Authors: Matthew S. Winston, William J. Wolf, F. Dean TosteAbstract:Two unique organometallic halide series (Ph3P)Au(4-Me-C6H4)(CF3)(X) and (Cy3P)Au(4-F-C6H4)(CF3)(X) (X = I, Br, Cl, F) have been synthesized. The PPh3-supported complexes can undergo both Caryl–X and Caryl–CF3 Reductive Elimination. Mechanistic studies of thermolysis at 122 °C reveal a dramatic reactivity and kinetic selectivity dependence on halide ligand. For X = I or F, zero-order kinetic behavior is observed, while for X = Cl or Br, kinetic studies implicate product catalysis. The selectivity for Caryl–CF3 bond formation increases in the order X = I < Br < Cl < F, with exclusively Caryl–I bond formation when X = I, and exclusively Caryl–CF3 bond formation when X = F. Thermodynamic measurements show that Au(III)–X bond dissociation energies increase in the order X = I < Br < Cl, and that ground state Au(III)–X bond strength ultimately dictates selectivities for Caryl–X and Caryl–CF3 Reductive Elimination.
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Photoinitiated oxidative addition of CF3I to gold(I) and facile aryl-CF3 Reductive Elimination.
Journal of the American Chemical Society, 2014Co-Authors: Matthew S. Winston, William J. Wolf, F. Dean TosteAbstract:Herein we report the mechanism of oxidative addition of CF3I to Au(I), and remarkably fast Caryl–CF3 bond Reductive Elimination from Au(III) cations. CF3I undergoes a fast, formal oxidative addition to R3PAuR′ (R = Cy, R′ = 3,5-F2-C6H4, 4-F-C6H4, C6H5, 4-Me-C6H4, 4-MeO-C6H4, Me; R = Ph, R′ = 4-F-C6H4, 4-Me-C6H4). When R′ = aryl, complexes of the type R3PAu(aryl)(CF3)I can be isolated and characterized. Mechanistic studies suggest that near-ultraviolet light (λmax = 313 nm) photoinitiates a radical chain reaction by exciting CF3I. Complexes supported by PPh3 undergo reversible phosphine dissociation at 110 °C to generate a three-coordinate intermediate that undergoes slow Reductive Elimination. These processes are quantitative and heavily favor Caryl–I Reductive Elimination over Caryl–CF3 Reductive Elimination. Silver-mediated halide abstraction from all complexes of the type R3PAu(aryl)(CF3)I results in quantitative formation of Ar–CF3 in less than 1 min at temperatures as low as −10 °C.
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Exceptionally fast carbon–carbon bond Reductive Elimination from gold(III)
Nature Chemistry, 2014Co-Authors: William J. Wolf, Matthew S. Winston, F. Dean TosteAbstract:Mechanistic studies of Reductive Elimination that forms aryl–aryl bonds from simple mono- and dinuclear gold phosphine complexes are disclosed. The observed rates for Reductive Elimination are unusually fast, even at temperatures as low as –52 °C, providing insight into the fundamental reactivity of oxidized organogold complexes. Reductive Elimination of carbon–carbon bonds occurs in numerous metal-catalysed reactions. This process is well documented for a variety of transition metal complexes. However, carbon–carbon bond Reductive Elimination from a limited number of Au( III ) complexes has been shown to be a slow and prohibitive process that generally requires elevated temperatures. Herein we show that oxidation of a series of mono- and bimetallic Au (I) aryl complexes at low temperature generates observable Au( III ) and Au (II) intermediates. We also show that aryl–aryl bond Reductive Elimination from these oxidized species is not only among the fastest observed for any transition metal, but is also mechanistically distinct from previously studied alkyl–alkyl and aryl–alkyl Reductive Eliminations from Au( III ).
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Exceptionally fast carbon–carbon bond Reductive Elimination from gold( III )
Nature chemistry, 2013Co-Authors: William J. Wolf, Matthew S. Winston, F. Dean TosteAbstract:Reductive Elimination of carbon-carbon bonds occurs in numerous metal-catalysed reactions. This process is well documented for a variety of transition metal complexes. However, carbon-carbon bond Reductive Elimination from a limited number of Au(III) complexes has been shown to be a slow and prohibitive process that generally requires elevated temperatures. Herein we show that oxidation of a series of mono- and bimetallic Au(I) aryl complexes at low temperature generates observable Au(III) and Au(II) intermediates. We also show that aryl-aryl bond Reductive Elimination from these oxidized species is not only among the fastest observed for any transition metal, but is also mechanistically distinct from previously studied alkyl-alkyl and aryl-alkyl Reductive Eliminations from Au(III).
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C(sp(3))-F Reductive Elimination from alkylgold(iii) fluoride complexes.
Chemical science, 2011Co-Authors: Neal P. Mankad, F. Dean TosteAbstract:Rare examples of C(sp3)–F Reductive Elimination were observed from several cis-F2Au(R)(IPr) intermediates generated by oxidation of (IPr)AuR complexes with XeF2. For R groups bearing β-hydrogens, β-hydride Elimination was competitive with C(sp3)–F Reductive Elimination. For strained cyclic R groups and most acyclic R groups lacking β-hydrogens, carbocation-like rearrangements occurred prior to C(sp3)–F Reductive Elimination. Kinetics of the decay of one cis-F2Au(R)(IPr) species, stereochemical analysis of Reductive Elimination with a chiral R group, and DFT analysis collectively suggest C(sp3)–F Reductive Elimination proceeding through transient cationic [(IPr)Au(F)(R)]+ intermediates with significant ionization of the Au–alkyl bonds.
Melanie S. Sanford - One of the best experts on this subject based on the ideXlab platform.
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C(sp3)–O Bond-Forming Reductive Elimination from PdIV with Diverse Oxygen Nucleophiles
Journal of the American Chemical Society, 2014Co-Authors: Nicole M. Camasso, Mónica H. Pérez-temprano, Melanie S. SanfordAbstract:This article describes an investigation of C(sp3)–O bond-forming Reductive Elimination reactions from PdIV complexes. Phenoxide, acetate, difluoroacetate, dimethylphosphate, tosylate, and nitrate nucleophiles are shown to participate in this reaction. In all cases, C(sp3)–O bond formation occurs with high selectivity over potentially competing C(sp2)–O coupling. Additives have a profound impact on the chemoselectivity of these Reductive Elimination reactions. An excess of RO– was found to limit competing C(sp3)–C(sp2) bond-forming Reductive Elimination, while the presence of Lewis acidic cations was found to suppress competing C(sp3)–F coupling. Mechanistic investigations were conducted, and the available data are consistent with a sequence involving pre-equilibrium dissociation of the oxyanion ligand (RO–) followed by nucleophilic attack of RO– on a cationic PdIV–alkyl intermediate.
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competition between sp3 c n vs sp3 c f Reductive Elimination from pdiv complexes
Journal of the American Chemical Society, 2014Co-Authors: Monica H Pereztemprano, Joy M Racowski, Jeff W Kampf, Melanie S. SanfordAbstract:This communication describes the design of a model system that allows direct investigation of competing sp3-C–N and sp3-C–F bond-forming Reductive Elimination from a PdIV fluoro sulfonamide complex. The Reductive Elimination selectivity varies dramatically as a function of reaction additives. A mechanism is proposed that provides a rationale for these effects.
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carbon heteroatom bond forming Reductive Elimination from palladium iv complexes
ChemInform, 2011Co-Authors: Joy M Racowski, Melanie S. SanfordAbstract:This work provides a comprehensive review (1986–2010) of the synthesis, characterization, and reactivity of palladium(IV) complexes that undergo carbon–heteroatom bond-forming Reductive Elimination reactions. In cases where mechanistic information is available, the molecular pathway for C–X bond formation is described in detail. Examples of catalytic transformations that may involve this mechanistic manifold are also presented.
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detailed study of c o and c c bond forming Reductive Elimination from stable c2n2o2 ligated palladium iv complexes
Journal of the American Chemical Society, 2009Co-Authors: Joy M Racowski, Allison R Dick, Melanie S. SanfordAbstract:This paper describes the synthesis of a series of PdIV complexes of general structure (N∼C)2PdIV(O2CR)2 (N∼C = a rigid cyclometalated ligand; O2CR = carboxylate) by reaction of (N∼C)2PdII with PhI(O2CR)2. The majority of these complexes undergo clean C−O bond-forming Reductive Elimination, and the mechanism of this process has been investigated. A variety of experiments, including Hammett plots, Eyring analysis, crossover studies, and investigations of the influence of solvent and additives, suggest that C−O bond-forming Reductive Elimination proceeds via initial carboxylate dissociation followed by C−O coupling from a 5-coordinate cationic PdIV intermediate. The mechanism of competing C−C bond-forming Reductive Elimination from these complexes has also been investigated and is proposed to involve direct Reductive Elimination from the octahedral PdIV centers.
