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–C⋯M 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.