Agostic interaction

From Wikipedia, the free encyclopedia

The word agostic was first coined for organometallic chemistry by Malcolm Green and Maurice Brookhart to describe a weak bonding interaction between a transition metal and a C-H bond on a carbon atom that is held close to the metal center through an additional π- or σ-bond.[1] It is derived from the Greek word for "to hold close to oneself". This interaction closely resembles the transition state of an oxidative addition or reductive elimination reaction. Agostic interactions are best demonstrated by crystallography, but can be inferred by the presence of a 1H NMR peak that is shifted upfield from that of a normal aryl or alkane. towards that of a hydride ligand. The coupling constant JCH is typically lowered to 70-100 Hz versus the 125 Hz expected for a normal sp3 carbon-hydrogen bond.

Agostic bonds sometimes play a role in catalysis by increasing 'rigidity' in transition states. For instance, in Ziegler-Natta catalysis the highly electrophilic metal center has agostic interactions with the growing polymer chain.[2]

The term agostic has incorrectly been extended to include other two-electron three-center bonding interactions such as the complexation of H2 to tungsten illustrated in W(CO)3(PPri3)2H2.[3]

[edit] References

  1. ^ Maurice Brookhart, Malcolm L. H. Green, Carbon-hydrogen-transition metal bonds. Journal of Organometallic Chemistry, 250(1), 395-408 (1983).
  2. ^ Reference
  3. ^ Kubas, G. J., "Metal Dihydrogen and σ-Bond Complexes", Kluwer Academic/Plenum Publishers: New York, 2001

[edit] Web Page

Warning: This template has been placed on a non talk page. This template should be placed on Talk pages only.
WikiProject on Chemistry
Portal:Chemistry
 Chemistry Portal
This article is within the scope of WikiProject Chemistry, which collaborates on Chemistry and related subjects on Wikipedia. To participate, help improve this article or visit the project page for details on the project.

Article Grading: The article has not been rated for quality and/or importance yet. Please rate the article and then leave comments here to explain the ratings and/or to identify the strengths and weaknesses of the article..
Retrieved from "http://en.wikipedia.org../../../a/g/o/Agostic_interaction.html"