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Thomas P Fehlner - One of the best experts on this subject based on the ideXlab platform.
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Ruthenacarboranes from the Reaction of nido-1,2-(Cp*RuH)2B3H7 with HC⋮CCO2Me, Cp* = η5-C5Me5. Hydrometalation, Alkyne Incorporation, and Functional Group Modification via Cooperative Metal−Boron Interactions within a Metallaborane Cluster Framework
Journal of the American Chemical Society, 2003Co-Authors: And Alicia M Beatty, Thomas P FehlnerAbstract:Reaction of nido-1,2-(Cp*RuH)2B3H7, 1, and methyl acetylene monocarboxylate under kinetic control generates nido-1,2-(Cp*Ru)2(μ-C{[CO2Me]Me})B3H7 (a pair of geometric isomers, 3 and 5) and nido-1,2-(Cp*Ru)2(1,3-μ-C{[CH2CO2Me]H})B3H7, 4, which display the first examples of exo-cluster μ-alkylidene Ru−B bridges generated by Hydrometalation of an alkyne on the cluster framework. Both 3 and 5, but not 4, rearrange into arachno-2,8-μ(C)-5-η1(O)-Me{CO2Me}C-1,2-(Cp*Ru)2B3H7, 2, in which an unprecedented intramolecular coordination of the carbonyl oxygen atom of the alkyne substituent to a boron framework site opens the ruthenaborane skeleton. Compound 2, in turn, is an intermediate in the formation of the ruthenacarborane nido-1,2-(Cp*Ru)2-3-OH-4-OMe-5-Me-4,5-C2B2H5, 12, in which the carbonyl−oxygen double bond has been cleaved as its oxygen atom inserts into a B−H bond and the carbonyl carbon inserts into the metallaborane framework. In a parallel reaction pathway, nido-1,2-(Cp*Ru)2-5-CO2Me-4,5-C2B2H7, 6, nido-...
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ruthenacarboranes from the reaction of nido 1 2 cp ruh 2b3h7 with hc cco2me cp η5 c5me5 Hydrometalation alkyne incorporation and functional group modification via cooperative metal boron interactions within a metallaborane cluster framework
Journal of the American Chemical Society, 2003Co-Authors: And Alicia M Beatty, Thomas P FehlnerAbstract:Reaction of nido-1,2-(Cp*RuH)2B3H7, 1, and methyl acetylene monocarboxylate under kinetic control generates nido-1,2-(Cp*Ru)2(μ-C{[CO2Me]Me})B3H7 (a pair of geometric isomers, 3 and 5) and nido-1,2-(Cp*Ru)2(1,3-μ-C{[CH2CO2Me]H})B3H7, 4, which display the first examples of exo-cluster μ-alkylidene Ru−B bridges generated by Hydrometalation of an alkyne on the cluster framework. Both 3 and 5, but not 4, rearrange into arachno-2,8-μ(C)-5-η1(O)-Me{CO2Me}C-1,2-(Cp*Ru)2B3H7, 2, in which an unprecedented intramolecular coordination of the carbonyl oxygen atom of the alkyne substituent to a boron framework site opens the ruthenaborane skeleton. Compound 2, in turn, is an intermediate in the formation of the ruthenacarborane nido-1,2-(Cp*Ru)2-3-OH-4-OMe-5-Me-4,5-C2B2H5, 12, in which the carbonyl−oxygen double bond has been cleaved as its oxygen atom inserts into a B−H bond and the carbonyl carbon inserts into the metallaborane framework. In a parallel reaction pathway, nido-1,2-(Cp*Ru)2-5-CO2Me-4,5-C2B2H7, 6, nido-...
Alois Furstner - One of the best experts on this subject based on the ideXlab platform.
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trans hydrogenation gem hydrogenation and trans Hydrometalation of alkynes an interim report on an unorthodox reactivity paradigm
Journal of the American Chemical Society, 2019Co-Authors: Alois FurstnerAbstract:cis-Delivery of H2 to the π-system of an unsaturated substrate is the canonical course of metal catalyzed hydrogenation reactions. The semireduction of internal alkynes with the aid of [Cp*Ru]-based catalysts violates this rule and affords E-alkenes by direct trans-hydrogenation. A pathway involving σ-complexes and metallacyclopropenes accounts for this unconventional outcome. Connected to this process is an even more striking reactivity mode, in which both H atoms of H2 are delivered to one and the same C atom. Such gem-hydrogenation of stable carbogenic compunds is a fundamentally new transformation that leads to the formation of discrete metal carbene complexes. Computational studies suggest that the trans- and the gem-pathway have similar barriers, but polar substituents in the vicinity of the reacting triple bond provide opportunities for imposing selectivity and control. Moreover, it is shown that catalytic trans-hydrogenation is by no means a singularity: rather, the underlying principle is also ma...
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ruthenium catalyzed alkyne trans Hydrometalation mechanistic insights and preparative implications
Journal of the American Chemical Society, 2017Co-Authors: Dragosadrian Rosca, Karin Radkowski, Larry M Wolf, Minal Wagh, Richard Goddard, Walter Thiel, Alois FurstnerAbstract:[Cp*RuCl]4 (1) has previously been shown to be the precatalyst of choice for stereochemically unorthodox trans-Hydrometalations of internal alkynes. Experimental and computational data now prove that the alkyne primarily acts as a four-electron donor ligand to the catalytically active metal fragment [Cp*RuCl] but switches to adopt a two-electron donor character once the reagent R3MH (M = Si, Ge, Sn) enters the ligand sphere. In the stereodetermining step the resulting loaded complex evolves via an inner-sphere mechanism into a ruthenacyclopropene which swiftly transforms into the product. In accord with the low computed barriers, spectral and preparative data show that the reaction is not only possible but sometimes even favored at low temperatures. Importantly, such trans-Hydrometalations are distinguished by excellent levels of regioselectivity when unsymmetrical alkynes are used that carry an −OH or −NHR group in vicinity of the triple bond. A nascent hydrogen bridge between the protic substituent and ...
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Hydroxyl-Assisted trans-Reduction of 1,3-Enynes: Application to the Formal Synthesis of (+)-Aspicilin
Synthesis, 2016Co-Authors: Sebastian Schaubach, Kenichi Michigami, Alois FurstnerAbstract:1,3-Enynes are hardly amenable to trans-Hydrometalation reactions, because they tend to bind the standard ruthenium catalysts too tightly. However, catalysts comprising a [Cp*Ru–Cl] unit allow such compounds to be used, provided they contain an OH group next to the triple bond. This aspect is illustrated by a formal synthesis of the lichen-derived macrolide aspicilin. The required macrocyclic enyne precursor was formed by an efficient ring-closing alkyne metathesis reaction.
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progress in the trans reduction and trans Hydrometalation of internal alkynes applications to natural product synthesis
Bulletin of the Chemical Society of Japan, 2016Co-Authors: Tobias Gylling Frihed, Alois FurstnerAbstract:The classical repertoire of synthetic organic chemistry is short of methods that allow triple bonds to be transformed into (E)-alkenes with high selectivity in the presence of other reducible sites...
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A Rhodium-Catalyzed C−H Activation/Cycloisomerization Tandem
Journal of the American Chemical Society, 2007Co-Authors: Christophe Aïssa, Alois FurstnerAbstract:A reaction cascade comprising a rhodium-catalyzed C−H activation, a subsequent Hydrometalation of an alkylidene cyclopropane in vicinity, regioselective C−C bond activation of the flanking cyclopropane ring, followed by reductive elimination of the resulting metallacycle, opens a new entry into functionalized cycloheptene derivatives. This crossover of C−H activation and higher order cycloaddition has been performed in two different formats, either using alkylidenecyclopropanes with a lateral vinylpyridine moiety or with a pending aldehyde group as the trigger. The reaction tolerates various functional groups, leaves chiral centers α to the reacting sites unaffected, and proceeds with excellent stereoselectivity. Labeling experiments support the proposed mechanism explaining the observed net cycloisomerization process.
And Alicia M Beatty - One of the best experts on this subject based on the ideXlab platform.
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Ruthenacarboranes from the Reaction of nido-1,2-(Cp*RuH)2B3H7 with HC⋮CCO2Me, Cp* = η5-C5Me5. Hydrometalation, Alkyne Incorporation, and Functional Group Modification via Cooperative Metal−Boron Interactions within a Metallaborane Cluster Framework
Journal of the American Chemical Society, 2003Co-Authors: And Alicia M Beatty, Thomas P FehlnerAbstract:Reaction of nido-1,2-(Cp*RuH)2B3H7, 1, and methyl acetylene monocarboxylate under kinetic control generates nido-1,2-(Cp*Ru)2(μ-C{[CO2Me]Me})B3H7 (a pair of geometric isomers, 3 and 5) and nido-1,2-(Cp*Ru)2(1,3-μ-C{[CH2CO2Me]H})B3H7, 4, which display the first examples of exo-cluster μ-alkylidene Ru−B bridges generated by Hydrometalation of an alkyne on the cluster framework. Both 3 and 5, but not 4, rearrange into arachno-2,8-μ(C)-5-η1(O)-Me{CO2Me}C-1,2-(Cp*Ru)2B3H7, 2, in which an unprecedented intramolecular coordination of the carbonyl oxygen atom of the alkyne substituent to a boron framework site opens the ruthenaborane skeleton. Compound 2, in turn, is an intermediate in the formation of the ruthenacarborane nido-1,2-(Cp*Ru)2-3-OH-4-OMe-5-Me-4,5-C2B2H5, 12, in which the carbonyl−oxygen double bond has been cleaved as its oxygen atom inserts into a B−H bond and the carbonyl carbon inserts into the metallaborane framework. In a parallel reaction pathway, nido-1,2-(Cp*Ru)2-5-CO2Me-4,5-C2B2H7, 6, nido-...
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ruthenacarboranes from the reaction of nido 1 2 cp ruh 2b3h7 with hc cco2me cp η5 c5me5 Hydrometalation alkyne incorporation and functional group modification via cooperative metal boron interactions within a metallaborane cluster framework
Journal of the American Chemical Society, 2003Co-Authors: And Alicia M Beatty, Thomas P FehlnerAbstract:Reaction of nido-1,2-(Cp*RuH)2B3H7, 1, and methyl acetylene monocarboxylate under kinetic control generates nido-1,2-(Cp*Ru)2(μ-C{[CO2Me]Me})B3H7 (a pair of geometric isomers, 3 and 5) and nido-1,2-(Cp*Ru)2(1,3-μ-C{[CH2CO2Me]H})B3H7, 4, which display the first examples of exo-cluster μ-alkylidene Ru−B bridges generated by Hydrometalation of an alkyne on the cluster framework. Both 3 and 5, but not 4, rearrange into arachno-2,8-μ(C)-5-η1(O)-Me{CO2Me}C-1,2-(Cp*Ru)2B3H7, 2, in which an unprecedented intramolecular coordination of the carbonyl oxygen atom of the alkyne substituent to a boron framework site opens the ruthenaborane skeleton. Compound 2, in turn, is an intermediate in the formation of the ruthenacarborane nido-1,2-(Cp*Ru)2-3-OH-4-OMe-5-Me-4,5-C2B2H5, 12, in which the carbonyl−oxygen double bond has been cleaved as its oxygen atom inserts into a B−H bond and the carbonyl carbon inserts into the metallaborane framework. In a parallel reaction pathway, nido-1,2-(Cp*Ru)2-5-CO2Me-4,5-C2B2H7, 6, nido-...
Dieter Lentz - One of the best experts on this subject based on the ideXlab platform.
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Organocatalytic C−F Bond Activation with Alanes
Chemistry - A European Journal, 2018Co-Authors: Alma D. Jaeger, Christian Ehm, Dieter LentzAbstract:© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. Hydrodefluorination reactions (HDF) of per- and polyfluorinated olefins and arenes by cheap aluminum alkyl hydrides in non-coordinating solvents can be catalyzed by O and N donors. TONs with respect to the organocatalysts of up to 87 have been observed. Depending on substrate and concentration, high selectivities can be achieved. For the prototypical hexafluoropropene, however, low selectivities are observed (E/Z≈2). DFT studies show that the preferred HDF mechanism for this substrate in the presence of donor solvents proceeds from the dimer Me 4 Al 2 (μ-H) 2 THF by nucleophilic vinylic substitution (S N V)-like transition states with low selectivity and without formation of an intermediate, not via hydrometallation or σ-bond metathesis. In the absence of donor solvents, hydrometallation is preferred but this is associated with inaccessibly high activation barriers at low temperatures. Donor solvents activate the aluminum hydride bond, lower the barrier for HDF significantly, and switch the product preference from Z to E. The exact nature of the donor has only a minimal influence on the selectivity at low concentrations, as the donor is located far away from the active center in the transition states. The mechanism changes at higher donor concentrations and proceeds from Me 2 AlHTHF via S N V and formation of a stable intermediate, from which elimination is unselective, which results in a loss of selectivity.
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competition of nucleophilic aromatic substitution σ bond metathesis and syn Hydrometalation in titanium iii catalyzed hydrodefluorination of arenes
Chemistry-an Asian Journal, 2016Co-Authors: Juliane Kruger, Jakob Leppkes, Dieter LentzAbstract:Several functionalized and non-functionalized perfluoroarenes are catalytically transformed into their para hydrodefluorinated (HDF) products by using catalytic amounts titanocene difluoride and stoichiometric amounts diphenylsilane. Turnover numbers (TON) up to 93 are observed. Solution DFT calculations at the M06-2X/TZ(PCM)//M06-2X/TZ(PCM) level of theory provide insight into the mechanism of Ti(III)-catalyzed aromatic HDF. Two different substrate approaches, with Ti-F interaction (pathway A) and without Ti-F interaction (pathway B), are possible. Pathway A leads to SBM TS, whereas pathway B proceeds via a two-step mechanism through a syn hydrometallation intermediate or through a Meisenheimer intermediate. Both pathways are competitive over a broad range of substrates.
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Competition of Nucleophilic Aromatic Substitution, σ‐Bond Metathesis, and syn Hydrometalation in Titanium(III)‐Catalyzed Hydrodefluorination of Arenes
Chemistry-an Asian Journal, 2016Co-Authors: Juliane Kruger, Jakob Leppkes, Dieter LentzAbstract:Several functionalized and non-functionalized perfluoroarenes are catalytically transformed into their para hydrodefluorinated (HDF) products by using catalytic amounts titanocene difluoride and stoichiometric amounts diphenylsilane. Turnover numbers (TON) up to 93 are observed. Solution DFT calculations at the M06-2X/TZ(PCM)//M06-2X/TZ(PCM) level of theory provide insight into the mechanism of Ti(III)-catalyzed aromatic HDF. Two different substrate approaches, with Ti-F interaction (pathway A) and without Ti-F interaction (pathway B), are possible. Pathway A leads to SBM TS, whereas pathway B proceeds via a two-step mechanism through a syn hydrometallation intermediate or through a Meisenheimer intermediate. Both pathways are competitive over a broad range of substrates.
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Hydrometalation of fluoroallenes
Dalton Transactions, 2009Co-Authors: Moritz F Kuhnel, Dieter LentzAbstract:Tetrafluoroallene (1) and 1,1-difluoroallene (2) react under mild conditions with group 6 and 7 transition metal hydride complexes Cp(CO)3MoH (4), CO5MnH (5), Cp2WH2 (9), and Cp2MoH2 (10) to give the new fluoropropenyl complexes 6a, 7a, 11, 12, 15a–c, and 16a–c, which were characterized by single crystal X-ray diffraction. Complexes 6a and 7a undergo thermally induced 1,3-fluorine migration, whereas 11 and 12 show hindered rotation around the carbon metal single bond.
Nobuharu Iwasawa - One of the best experts on this subject based on the ideXlab platform.
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silyl ligand mediated reversible β hydrogen elimination and Hydrometalation at palladium
Chemistry: A European Journal, 2014Co-Authors: Jun Takaya, Nobuharu IwasawaAbstract:The mechanism and origin of the facile β-hydrogen elimination and Hydrometalation of a palladium complex bearing a phenylene-bridged PSiP pincer ligand are clarified. Experimental and theoretical studies demonstrate a new mechanism for β-hydrogen elimination and Hydrometalation mediated by a silyl ligand at palladium, which enables direct interconversion between an ethylpalladium(II) complex and an η2-(Si-H)palladium(0) complex without formation of a square-planar palladium(II) hydride intermediate. The flexibility of the PSiP pincer ligand enables it to act as an efficient scaffold to deliver the hydrogen atom as a hydride ligand.
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Silyl Ligand Mediated Reversible β‐Hydrogen Elimination and Hydrometalation at Palladium
Chemistry: A European Journal, 2014Co-Authors: Jun Takaya, Nobuharu IwasawaAbstract:The mechanism and origin of the facile β-hydrogen elimination and Hydrometalation of a palladium complex bearing a phenylene-bridged PSiP pincer ligand are clarified. Experimental and theoretical studies demonstrate a new mechanism for β-hydrogen elimination and Hydrometalation mediated by a silyl ligand at palladium, which enables direct interconversion between an ethylpalladium(II) complex and an η2-(Si-H)palladium(0) complex without formation of a square-planar palladium(II) hydride intermediate. The flexibility of the PSiP pincer ligand enables it to act as an efficient scaffold to deliver the hydrogen atom as a hydride ligand.
