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Coexistence of lewis acid and base functions: a generalized view of the frustrated lewis pair concept with novel implications for reactivity


Berke, H; Jiang, Y; Yang, X; Jiang, C; Chakraborty, S; Landwehr, A (2013). Coexistence of lewis acid and base functions: a generalized view of the frustrated lewis pair concept with novel implications for reactivity. In: Erker, G; Stephan, D W. Frustrated Lewis Pairs II. Heidelberg New York Dordrecht London: Springer, 27-57.

Abstract

Sterically congested Lewis pairs cannot form Lewis adducts; instead they establish encounter complexes of “frustrated” Lewis pairs (FLPs). These encounter complexes have recently been recognized to be capable of activating, i.e., splitting, homopolar and polar single and double bonds, which rendered a new reactivity principle. With the help of qualitative orbital considerations this chapter reviews and explains the reactivity of FLPs toward homopolar Z–Z or Z–Z′ single bonded molecules, such as H–H and C–H single bonds, assuming in the encounter complexes the action of strongly polarizing Coulombic fields originating from the FLP constituents. This reactivity principle has been extended in its view to the activating potential for homopolar Z–Z or Z–Z′ single bonds of strongly polarized [X–Y ↔ X(+)–Y|(−)] σ and [X=Y ↔ X(+)–Y|(−)] π bonded molecules (X,Y = atoms or molecular fragments; electronegativity of X < electronegativity of Y). A striking analogy in the reaction behavior of FLPs and strongly polarized σ and π bonded molecules could be revealed based on the analyses of selected examples of “metal-free” (main group element reactions) or metal-based (containing transition metals) σ bond metathesis reactions and σ bond additions of H2 and alkanes to polarized main group element and metal to ligand π bonds. Related to the described polar reaction types are Z,Z′ double atom or group transfers between highly polarized double bonds of XY and X′Y′ molecules combining a Z,Z′ elimination with an addition process. Multiple consecutive Z,Z′ double atom or group transfers are denoted as double H transfer cascade reactions. Analyzed by examples are concerted or stepwise double H transfers and double H transfer cascades with Z,Z′=H,H from the “metal-free” and metal-based realms: the Meerwein– Pondorf–Verley reduction, H,H exchanges between amine boranes and between amine boranes and unsaturated organic compounds, and the crucial H,H transfer steps of Noyori’s bifunctional and Shvo type transfer hydrogenation catalyses.

Abstract

Sterically congested Lewis pairs cannot form Lewis adducts; instead they establish encounter complexes of “frustrated” Lewis pairs (FLPs). These encounter complexes have recently been recognized to be capable of activating, i.e., splitting, homopolar and polar single and double bonds, which rendered a new reactivity principle. With the help of qualitative orbital considerations this chapter reviews and explains the reactivity of FLPs toward homopolar Z–Z or Z–Z′ single bonded molecules, such as H–H and C–H single bonds, assuming in the encounter complexes the action of strongly polarizing Coulombic fields originating from the FLP constituents. This reactivity principle has been extended in its view to the activating potential for homopolar Z–Z or Z–Z′ single bonds of strongly polarized [X–Y ↔ X(+)–Y|(−)] σ and [X=Y ↔ X(+)–Y|(−)] π bonded molecules (X,Y = atoms or molecular fragments; electronegativity of X < electronegativity of Y). A striking analogy in the reaction behavior of FLPs and strongly polarized σ and π bonded molecules could be revealed based on the analyses of selected examples of “metal-free” (main group element reactions) or metal-based (containing transition metals) σ bond metathesis reactions and σ bond additions of H2 and alkanes to polarized main group element and metal to ligand π bonds. Related to the described polar reaction types are Z,Z′ double atom or group transfers between highly polarized double bonds of XY and X′Y′ molecules combining a Z,Z′ elimination with an addition process. Multiple consecutive Z,Z′ double atom or group transfers are denoted as double H transfer cascade reactions. Analyzed by examples are concerted or stepwise double H transfers and double H transfer cascades with Z,Z′=H,H from the “metal-free” and metal-based realms: the Meerwein– Pondorf–Verley reduction, H,H exchanges between amine boranes and between amine boranes and unsaturated organic compounds, and the crucial H,H transfer steps of Noyori’s bifunctional and Shvo type transfer hydrogenation catalyses.

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Additional indexing

Item Type:Book Section, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:2013
Deposited On:23 Jan 2014 10:28
Last Modified:05 Apr 2016 17:30
Publisher:Springer
ISSN:0340-1022
ISBN:978-3-642-37758-7
Publisher DOI:https://doi.org/10.1007/128_2012_400

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