Agostic interaction

Formation of a 3-center 2-electron bond between a transition metal and C–H bond

In organometallic chemistry, agostic interaction refers to the intramolecular interaction of a coordinatively-unsaturated transition metal with an appropriately situated C−H bond on one of its ligands. The interaction is the result of two electrons involved in the C−H bond interaction with an empty d-orbital of the transition metal, resulting in a three-center two-electron bond. It is a special case of a C–H sigma complex. Historically, agostic complexes were the first examples of C–H sigma complexes to be observed spectroscopically and crystallographically, due to intramolecular interactions being particularly favorable and more often leading to robust complexes. Many catalytic transformations involving oxidative addition and reductive elimination are proposed to proceed via intermediates featuring agostic interactions. Agostic interactions are observed throughout organometallic chemistry in alkyl, alkylidene, and polyenyl ligands.

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