Document Detail


Coexistence of Lewis Acid and Base Functions: A Generalized View of the Frustrated Lewis Pair Concept with Novel Implications for Reactivity.
MedLine Citation:
PMID:  23306869     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
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 H(2) 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.
Authors:
Heinz Berke; Yanfeng Jiang; Xianghua Yang; Chunfang Jiang; Subrata Chakraborty; Anne Landwehr
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2013-1-11
Journal Detail:
Title:  Topics in current chemistry     Volume:  -     ISSN:  0340-1022     ISO Abbreviation:  Top Curr Chem     Publication Date:  2013 Jan 
Date Detail:
Created Date:  2013-1-11     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0432204     Medline TA:  Top Curr Chem     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Affiliation:
Anorganisch-chemisches Institut, Universität Zürich, Winterthurer Strasse 190, 8057, Zürich, Switzerland, hberke@aci.uzh.ch.
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