Intramolecular C-C agostic complexes: C-C sigma interactions by another name.

In this comprehensive review the developments in the synthesis, characterization and reactivity of complexes (s-, d- and f-block) in which a C-C single bond interacts with a metal centre are discussed: so called C-CM agostic complexes. Such species are of significant interest with regard to structure and bonding, the activation of C-C single bonds and, thus, catalytic methods of C-C bond formation (or activation). Examples of C-C agostic complexes of early and later transition metals, actinides and group 1 metals are discussed, along with C-C agostic interactions in metallacyclobutanes. Examples of Si-Si∙∙∙M, B-C∙∙∙M and B-B∙∙∙M agostic interactions are also presented. Throughout, the structural, spectroscopic and computational markers that indicate the likely presence of a C-C∙∙∙M agostic interaction in a complex are highlighted.