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Digitale Medien

Mechanisms of Cyclopalladation Reactions in Acetic Acid: Not So Simple One-Pot Processes (2000)

Gómez, Montserrat ; Granell, Jaume ; Martinez, Manuel

Weinheim : Wiley-Blackwell

Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 217-224

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ISSN: 1434-1948

Schlagwort(e): Reaction mechanisms ; Cyclopalladation ; Acetic acid ; Pd-C bond stability ; Polynuclear species ; Palladium ; Chemistry ; General Chemistry

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: The processes operating during the synthetic cyclopalladation reactions of imines in acetic acid have been studied from a kinetico-mechanistic point of view. These reactions include a fast initial coordination to the palladium through the N-donor atom of the imine, followed by the proper C-H bond activation to produce the acetato bridged dimeric species. At this point, the lability of the bridging acetato groups, the hydrolysis of the C-Pd bonds, and/or the hydrolysis of C=N exo bonds contribute to the generation of dark red polynuclear compounds. The processes occurring after the C-H activation have been followed kinetically, both from palladium acetate plus imine, and the synthetically pure isolated acetato dimers as starting materials. The kinetic and activation parameters have been found identical within experimental error whatever the starting material was (k323 = 1.5 × 10-4 s-1; ΔH# = 51 kJ mol-1; ΔS# = -163 JK-1 mol-1 ΔV# = +19 cm3 mol-1 for the 4-ClC6H4-CH=N-CH2-C6H5 imine derivative 1a). Acidolysis of C-Pd bonds has been found to occur in these polynuclear species. When alternative monomeric Cbenzylic-Pd bond-containing complexes are possible follow ups of the reactions produce them as final dead-end complexes (k323 = 2.2 × 10-5 s-1; ΔH# = 61 kJ mol-1; ΔS# = JK-1 mol-1 ΔV# ≈ 0 cm3 cm-1 for the [2,4,6-(CH3)3]C6H2-CH=N-CH2-[2-(CH3]C6[H4] imine derivative 3d). The same study has been carried out with primary amines in order to check the validity of the data if C=N bond hydrolysis is taking place in the imine derivatives with exo C=N bonds. For complexes with similar type of metallacycles, the results agree reasonably well with the proposed mechanism [k323 = 1.2·10-4 s-1, ΔH# = 46 kJ·mol-1, ΔS# = -180 J·K-1mol-1, ΔV# = -16 cm3·mol-1 for the polynuclear formation of the C6H5-CH2-NH2 derivative 4e; k323 = 3.0·10-4 s-1, ΔH# = 55 kJ·mol-1, ΔS

Zusätzliches Material: 1 Ill.

Materialart: Digitale Medien

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Digitale Medien

Quantitative morphological changes in neurons and glia in the frontal lobe of the aging rat (1993)

Peinado, Maria Angeles ; Martinez, Manuel ; Pedrosa, Juán Angel ; [weitere]

New York, NY [u.a.] : Wiley-Blackwell

The @Anatomical Record 237 (1993), S. 104-108

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ISSN: 0003-276X

Schlagwort(e): Neuronal density ; Glial density ; Cytomorphometry ; Old ; Life and Medical Sciences ; Cell & Developmental Biology

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Medizin

Notizen: The quantitative morphological changes in neurons and glia during the aging process were analyzed in the different cortical layers, grouped as I, II-IV, V, and VI, of the frontal cortex of the rat. The parameters analyzed were cortical volume, neuronal density, glial density, and neuronal soma and nucleus areas. No changes with age were found in the volume of the layers, in neuronal density (with the exception of layer I), or in the area of the neuronal soma. However, older animals showed a 10 to 20% increase in glial density, depending on the layer studied. In addition, there was an age-related decrease in the area of the neuronal nucleus in layers II-IV, V, and VI. These results support the idea that the aging frontal cortex undergoes structural changes that may be involved in the morphological basis of memory and cognitive impairments characteristic of aging. © 1993 Wiley-Liss, Inc.

Zusätzliches Material: 4 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/ar.1092370110

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