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Transmetalation Reaction (transmetalation + reaction)

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Chemistry100%

Selected Abstracts

Transmetalation Reactions from Fischer Carbene Complexes to Late Transition Metals: A DFT Study

CHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2008
Israel Fernández Dr.
Abstract Transmetalation reactions from chromium(0) Fischer carbene complexes to late-transition-metal complexes (palladium(0), copper(I), and rhodium(I)) have been studied computationally by density functional theory. The computational data were compared with the available experimental data. In this study, the different reaction pathways involving the different metal atoms have been compared with each other in terms of their activation barriers and reaction energies. Although the reaction profiles for the transmetalation reactions to palladium and copper are quite similar, the computed energy values indicate that the process involving palladium as catalyst is more favorable than that involving copper. In contrast to these transformations, which occur via triangular heterobimetallic species, the transmetalation reaction to rhodium leads to a new heterobimetallic species in which a carbonyl ligand is also transferred from the Fischer carbene to the rhodium catalyst. Moreover, the structure and bonding situation of the so far elusive heterobimetallic complexes are briefly discussed. La reacción de transmetalación catalítica desde cromo(0) Fischer carbenos a metales de transición tardía (Pd0, CuIand RhI) se ha estudiado computacionalmente usando DFT. Los resultados computacionales se han comparado con los datos experimentales disponibles. Las barreras y las energías de reacción se han comparado en los caminos de reacción obtenidos para los metales considerados. Mientras que los perfiles de reacción para la transmetalación desde Cr a Pd o Cu son similares, los valores calculados indican que aquellos procesos que implican catalizadores de Pd son más favorables que los que implican Cu. En claro contraste con estas transformaciones, que ocurren a través de especies heterobimetálicas con geometría triangular, la reacción con Rh forma nuevas especies heterobimetálicas en las que se ha transferido un ligando carbonilo desde el complejo de Fischer al catalizador de Rh. Adicionalmente, se discute la estructura y la forma de enlace de éstos complejos heterobimetálicos no aislados hasta este momento. [source]

First Example of a Gold(I) N -Heterocyclic-Carbene-Based Initiator for the Bulk Ring-Opening Polymerization of L -Lactide

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2006
Lipika Ray
Abstract Synthesis, structure, and catalysis studies of two Au- and Ag-based initiators, namely, [3-(N - tert -butylacetamido)-1-(2-hydroxycyclohexyl)imidazol-2-ylidene]AuCl (1c) and [3-(N - tert -butylacetamido)-1-(2-hydroxycyclohexyl)imidazol-2-ylidene]AgCl (1b), for the bulk ring-opening polymerization of L -lactide are reported. Specifically, gold complex 1c was obtained from silver complex 1b by the transmetalation reaction with (SMe2)AuCl. Silver complex 1b was synthesized by the treatment of 3-(N - tert -butylacetamido)-1-(2-hydroxycyclohexyl)imidazolium chloride (1a) with Ag2O. Compound 1a was synthesized directly from the reaction of N - tert -butyl-2-chloroacetamide, cyclohexene oxide, and imidazole. The molecular structures of 1a, 1b, and 1c have been determined by X-ray diffraction studies. The formation of neutral monomeric complexes with linear geometries at the metal centers was observed for both 1b and 1c. The Au and Ag complexes 1c and 1b successfully catalyzed the bulk ring-opening polymerization of L -lactide at elevated temperatures under solvent-free melt conditions to produce moderate to low molecular weight polylactide polymers with narrow molecular weight distributions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Transmetalation Reactions from Fischer Carbene Complexes to Late Transition Metals: A DFT Study

CHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2008
Israel Fernández Dr.
Abstract Transmetalation reactions from chromium(0) Fischer carbene complexes to late-transition-metal complexes (palladium(0), copper(I), and rhodium(I)) have been studied computationally by density functional theory. The computational data were compared with the available experimental data. In this study, the different reaction pathways involving the different metal atoms have been compared with each other in terms of their activation barriers and reaction energies. Although the reaction profiles for the transmetalation reactions to palladium and copper are quite similar, the computed energy values indicate that the process involving palladium as catalyst is more favorable than that involving copper. In contrast to these transformations, which occur via triangular heterobimetallic species, the transmetalation reaction to rhodium leads to a new heterobimetallic species in which a carbonyl ligand is also transferred from the Fischer carbene to the rhodium catalyst. Moreover, the structure and bonding situation of the so far elusive heterobimetallic complexes are briefly discussed. La reacción de transmetalación catalítica desde cromo(0) Fischer carbenos a metales de transición tardía (Pd0, CuIand RhI) se ha estudiado computacionalmente usando DFT. Los resultados computacionales se han comparado con los datos experimentales disponibles. Las barreras y las energías de reacción se han comparado en los caminos de reacción obtenidos para los metales considerados. Mientras que los perfiles de reacción para la transmetalación desde Cr a Pd o Cu son similares, los valores calculados indican que aquellos procesos que implican catalizadores de Pd son más favorables que los que implican Cu. En claro contraste con estas transformaciones, que ocurren a través de especies heterobimetálicas con geometría triangular, la reacción con Rh forma nuevas especies heterobimetálicas en las que se ha transferido un ligando carbonilo desde el complejo de Fischer al catalizador de Rh. Adicionalmente, se discute la estructura y la forma de enlace de éstos complejos heterobimetálicos no aislados hasta este momento. [source]

The Kinetic Acidity of Oligofluorobenzenes Correlated with Their Gas Phase Deprotonation Energies

CHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2005
Manfred Schlosser Prof. Dr.
Abstract The relative reactivities of fluorobenzene, all di-, tri-, and tetrafluorobenzenes and pentafluorobenzene toward sec -butyllithium have been assessed in tetrahydrofuran at ,100,°C. At this temperature no subsequent transmetalation reactions take place but those compromise the outcome of the competition experiments if the latter are conducted at ,75,°C. The rates determined at ,100,°C reflect the basicity differences between the naked (oligo)fluorophenyl anions to the extent of 10,%. [source]