The σ‐CAM Mechanism: σ Complexes as the Basis of σ‐Bond Metathesis at Late‐Transition‐Metal Centers
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- 23 March 2007
- journal article
- review article
- Published by Wiley in Angewandte Chemie International Edition in English
- Vol. 46 (15) , 2578-2592
- https://doi.org/10.1002/anie.200603224
Abstract
Complexes in which a σ‐HE bond (E=H, B, Si, C) acts as a two‐electron donor to the metal center are called σ complexes. Clues that it is possible to interconvert σ ligands without a change in oxidation state derive from CH activation reactions effecting isotope exchange and from dynamic rearrangements of σ complexes (see Frontispiece). Through these pathways, metathesis of ME bonds can occur at late transition metals. We call this process σ‐complex‐assisted metathesis, or σ‐CAM, which is distinct from the familiar σ‐bond metathesis (typical for d0 metals and requiring no intermediate) and from oxidative‐reductive elimination mechanisms (inherently requiring intermediates with changed oxidation states and sometimes involving σ complexes). There are examples of σ‐CAM mechanisms in catalysis, especially for alkane borylation and isotope exchange of alkanes. It may also occur in silylation and alkene hydrogenation.Keywords
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