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  • C-H bond  (1)
  • Transition metals  (1)
  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Theoretical chemistry accounts 87 (1994), S. 277-292 
    ISSN: 1432-2234
    Schlagwort(e): Acetylene ; C-H bond ; 2nd row transition metals ; Activation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The C-H activation reaction of acetylene by second row transition metal atoms has been studied including electron correlation of all valence electrons. Binding energies have been computed for both π-coordinated complexes and C-H insertion products. It is found that for most atoms the π-coordinated complexes are thermodynamically favoured, just as in the case for the corresponding ethylene reaction. The barrier height for the C-H insertion increases from acetylene to ethylene and to methane. This is in line with the experimental finding that there should be an inverse relation between C-H bond strengths and the difficulty to activate these bonds. To explain the detailed differences between the C-H activation of acetylene and ethylene, the interaction with two, rather than one, π- and π*-orbitals for acetylene is of key importance. The barrier height for the acetylene reaction increases significantly between niobium and molybdenum going to the right in the periodic table, just as for all oxidative addition reactions previously studied. The origin of this increase is that noibium has one empty 4d-orbital but for molybdenum all 4d-orbitals are occupied. Rhodium has the lowest barrier for C-H activation for all systems studied.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Theoretical chemistry accounts 87 (1994), S. 267-275 
    ISSN: 1432-2234
    Schlagwort(e): Transition metals ; d-spaces ; SCF-CI ; Metal atom
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The possibility to use atomic basis sets with only twod-functions describing the metal atom has been investigated, both at the SCF and the CI levels, for the Ni and Pd atoms, their mono-hydrides and their mono-oxides. Using a general contraction scheme, two atomicd-orbitals, corresponding to two of the atomic configurationss 2 d 8,s 1 d 9 ands 0 d 10 were used as the twod-type basis functions. A surprisingly large part of the correlation effect on both atomic excitation energies and on the equilibrium distance and dissociation energies of the hydrides and the oxides was obtained using these small basis sets. It is argued that the reason for this is important “near-degeneracy” effects involving different atomicd-configurations and not dynamic correlation effects.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
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