The Experts below are selected from a list of 39 Experts worldwide ranked by ideXlab platform
Véronique Gouverneur - One of the best experts on this subject based on the ideXlab platform.
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Stereospecific anti SE2′ fluorination of allenylsilanes: synthesis of enantioenriched propargylic fluorides
Organic & biomolecular chemistry, 2008Co-Authors: Laurence Carroll, Samantha Mccullough, Thomas L. Rees, Timothy D. W. Claridge, Véronique GouverneurAbstract:The electrophilic fluorodesilylation of enantioenriched allenylsilanes proceeds with efficient transfer of chirality. The silylation–fluorination of propargylic alcohols occurs with overall retention of stereochemistry, a result consistent with a stereospecific anti SE2′ Mechanism for the fluorination step.
Yongho Kim - One of the best experts on this subject based on the ideXlab platform.
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Kinetic Isotope Effects as a Probe for the Protonolysis Mechanism of Alkylmetal Complexes: VTST/MT Calculations Based on DFT Potential Energy Surfaces.
Inorganic chemistry, 2016Co-Authors: Binh Khanh Mai, Yongho KimAbstract:Protonolysis by platinum or palladium complexes has been extensively studied because it is the microscopic reverse of the C–H bond activation reaction. The protonolysis of (COD)PtIIMe2, which exhibits abnormally large kinetic isotope effects (KIEs), is proposed to occur via a concerted pathway (SE2 Mechanism) with large tunneling. However, further investigation of KIEs for the protonolysis of ZnMe2 and others led to a conclusion that there is no noticeable correlation between the Mechanism and magnitude of KIE. In this study, we demonstrated that variational transition state theory including multidimensional tunneling (VTST/MT) could accurately predict KIEs and Arrhenius parameters of the protonolysis of alkylmetal complexes based on the potential energy surfaces generated by density functional theory. The predicted KIEs, EaD – EaH values, and AH/AD ratios for the protonolysis of (COD)PtIIMe2 and ZnIIMe2 by TFA agreed very well with experimental values. The protonolysis of ZnMe2 with the concerted pathway...
Mona Hosseini-sarvari - One of the best experts on this subject based on the ideXlab platform.
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Synthesis and Suzuki-Miyaura Cross-Coupling of Enantioenriched Secondary Potassium β-Trifluoroboratoamides: Catalytic, Asymmetric Conjugate Addition of Bisboronic Acid and Tetrakis(dimethylamino)diboron to α,β-Unsaturated Carbonyl Compounds.
Advanced synthesis & catalysis, 2013Co-Authors: Gary A. Molander, Steven R. Wisniewski, Mona Hosseini-sarvariAbstract:Enantioenriched potassium β-trifluoroboratoamides have been synthesized via an asymmetric, copper-catalyzed 1,4-addition of tetrahydroxydiboron (BBA) and tetrakis(dimethylamino)diboron to α,β-unsaturated amides. These dibora reagents provide access to the desired organotrifluoroborates using effective and atom economical sources of boron. The copper-catalyzed β-boration is extended to α,β-unsaturated ketones and esters. Desired potassium organotrifluoroborates are synthesized with yields up to 92% and enantiomeric ratios up to 98:2. The enantioenriched potassium β-trifluoroboratoamides are successfully cross-coupled with an array of aryl and heteroaryl chlorides in high yield with complete stereochemical fidelity as the transmetalation proceeds through an SE2 Mechanism via an open transition state.
Lars Ivar Elding - One of the best experts on this subject based on the ideXlab platform.
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Protonolysis of Dialkyl- and Alkylarylplatinum(II) Complexes and Geometrical Isomerization of the Derived Monoorgano-Solvento Complexes: Clear-Cut Examples of Associative and Dissociative Pathways in Platinum(II) Chemistry.
Inorganic chemistry, 1997Co-Authors: Rafaello Romeo, Maria Rosaria Plutino, Lars Ivar EldingAbstract:SynopsisProtonolysis of the title compounds involves rate-determining proton transfer to the substrate. Subsequent isomerization is dissociative. Activation volumes for the two processes have opposite signs. A new kinetic β-hydrogen accelerating effect for isomerization favoring the fluxionality of a T-shaped 14-electron intermediate is reported.AbstractProtonolysis of the complexes cis-[PtR2(PEt3)2] (R = Me, Et, Prn, Bun, CH2C(Me)3, CH2Si(Me)3) and cis-[Pt(R)(R‘)(PEt3)2] (R = Ph, 2-MeC6H4, 2,4,6-Me3C6H2; R‘ = Me) in methanol selectively cleaves one alkyl group, yielding cis-[Pt(R)(PEt3)2(MeOH)]+ and alkanes. The reactions occur as single-stage conversions from the substrate to the product. There is no evidence by UV and by low-temperature 1H and 31P NMR spectroscopy for the presence of significant amounts of Pt(II) or Pt(IV) intermediate species. Reactions are first order with respect to complex and proton concentrations and are strongly retarded by steric congestion at the Pt−C bond, varying from k2 = (2.65 ± 0.08) × 105 M-1 s-1 for R = R‘ = Et to k2 = 9.80 ± 0.44 M-1s-1 for R = R‘= CH2Si(Me)3. Low enthalpies of activation and largely negative volumes of activation are associated with the process. The Mechanism involves a rate-determining proton transfer either to the metal−carbon σ bond (SE2 Mechanism) or to the metal center (SE(oxidative) Mechanism), followed by fast extrusion of the alkane and simultaneous blocking of the vacant coordination site by the solvent to generate cis-[Pt(R)(PEt3)2(MeOH)]+ species. The subsequent slower process, cis to trans isomerization of cis-[Pt(R)(PEt3)2(MeOH)]+, is characterized by high values of enthalpies of activation, positive entropies of activation, and largely positive volumes of activation. The reaction is shown to proceed through the dissociative loss of the weakly bonded molecule of solvent and the interconversion of two geometrically distinct T-shaped 14-electron 3-coordinate intermediates. The presence of β-hydrogens on the residual alkyl chain produces a great acceleration of the rate (R = Me, ki = 0.0026 s-1; R = Et, ki = 44.9 s-1) as a consequence of the stabilization of the 3-coordinate [Pt(R)(PEt3)2]+ transition state through an incipient agostic interaction. The results of this work, together with those of a previous paper, give a rationale of the “elusive” nature of these compounds. The following factors concur: (i) electron release by the phosphine ligands, (ii) steric repulsion and distortion of the square-planar configuration, and (iii) interaction of the metal with β-hydrogens.
Laurence Carroll - One of the best experts on this subject based on the ideXlab platform.
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Stereospecific anti SE2′ fluorination of allenylsilanes: synthesis of enantioenriched propargylic fluorides
Organic & biomolecular chemistry, 2008Co-Authors: Laurence Carroll, Samantha Mccullough, Thomas L. Rees, Timothy D. W. Claridge, Véronique GouverneurAbstract:The electrophilic fluorodesilylation of enantioenriched allenylsilanes proceeds with efficient transfer of chirality. The silylation–fluorination of propargylic alcohols occurs with overall retention of stereochemistry, a result consistent with a stereospecific anti SE2′ Mechanism for the fluorination step.