Quantum Chemical Calculations with the Inclusion of Nonspecific and Specific Solvation: Asymmetric Transfer Hydrogenation with Bifunctional Ruthenium Catalysts.
In: Journal of the American Chemical Society, Jg. 135 (2013-02-20), Heft 7, S. 2604-2619
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Zugriff:
Details of the mechanism of asymmetric transfer hydrogenation of ketones catalyzed by two chiral bifunctional ruthenium complexes, (S)-RuH[(R,R)-OCH(Ph)CH(Ph)NH2](η6-benzene) (Ru-1) or (S)-RuH[(R,R)-p-TsNCH(Ph)CH(Ph)NH2](η?6-mesitylene) (Ru-2), were studied computationally by density functional theory, accounting for the solvation effects by using continuum, discrete, and mixed continuum/discrete solvation models via "solvated supermolecules" approach. In contrast to gas phase quantum chemical calculations, where the reactions were found to proceed via a concerted three-bond asynchronous process through a six-membered pericyclic transition state, incorporation of the implicit and/or explicit solvation into the calculations suggests that the same reactions proceed via two steps in solution: (i) enantio-determining hydride transfer and (ii) proton transfer through the contact ion-pair intermediate, stabilized primarily by ionic hydrogen bonding between the cation and the anion. The calculations suggest that the proton source for neutralizing the chiral RO- anion may be either the amine group of the cationic Ru complex or, more likely, a protic solvent molecule. In the latter case, the reaction may not necessarily proceed via the 16e amido complex Ru[(R,R)-XCH(Ph)CH(Ph)NH](η6-arene). The origin of enantioselectivity is discussed in terms of the newly formulated mechanism. [ABSTRACT FROM AUTHOR]
Titel: |
Quantum Chemical Calculations with the Inclusion of Nonspecific and Specific Solvation: Asymmetric Transfer Hydrogenation with Bifunctional Ruthenium Catalysts.
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Autor/in / Beteiligte Person: | Dub, Pavel A. ; Ikariya, Takao |
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Zeitschrift: | Journal of the American Chemical Society, Jg. 135 (2013-02-20), Heft 7, S. 2604-2619 |
Veröffentlichung: | 2013 |
Medientyp: | academicJournal |
ISSN: | 0002-7863 (print) |
DOI: | 10.1021/ja3097674 |
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