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- Brandt, Peter, et al.
(författare)
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Chromium-salen-mediated alkene epoxidation : a theoretical and experimental study indicates the importance of spin-surface crossing and the presence of a discrete intermediate.
- 2002
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Ingår i: Chemistry - A European Journal. - 0947-6539 .- 1521-3765. ; 8:18, s. 4299-307
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism of alkene epoxidation by chromium(v) oxo salen complexes has been studied by DFT and experimental methods. The reaction is compared to the closely related Mn-catalyzed process in an attempt to understand the dramatic difference in selectivity between the two systems. Overall, the studies show that the reactions have many similarities, but also a few critical differences. In agreement with experiment, the chromium system requires a change from low- to high-spin in the catalytic cycle, whereas the manganese system can proceed either with spin inversion or entirely on the high-spin surface. The low-spin addition of metal oxo species to an alkene leads to an intermediate which forms epoxide either with a barrier on the low-spin surface or without a barrier after spin inversion. Supporting evidence for this intermediate was obtained by using vinylcyclopropane traps. The chromium(v) oxo complexes can adopt a stepped shape or form a more concave surface, analogous to previous results on manganese salen complexes.
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| 2. |
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| 3. |
- Brandt, Peter, et al.
(författare)
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Molecular Mechanics (MM3) Parameters for Ruthenium(II)-Polypyridyl Complexes.
- 1998
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Ingår i: Inorganic Chemistry. - 0020-1669 .- 1520-510X. ; 37:16, s. 4120-4127
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Tidskriftsartikel (refereegranskat)abstract
- We have developed molecular mechanics parameters for Ru(II)-polypyridyl coordination compounds with the MM3 force field in MacroModel. X-ray structures, together with a B3LYP frequency calculation on a model system, have been utilized in the parametrization. The performance of the force field and the quality of each parameter is analyzed. A clear qualitative correlation have been found between coordination geometry and emission properties for the ruthenium polypyridyl complexes examined in this paper.
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