  Agostic interactions are covalent intramolecular interactions between an
electron deficient metal and a sigma-bond in close geometrical proximity to the
metal atom. While the classic cases involve CH sigma-bonds close to early
transition metals like titanium, many more agostic systems have been proposed
which contain CH, SiH, BH, CC and SiC sigma-bonds coordinated to a wide range
of metal atoms. Recent computational studies of a multitude of agostic
interactions are reviewed in this contribution. It is highlighted how several
difficulties with the theoretical description of the phenomenon arise because
of the relative weakness of this interaction. The methodology used to compute
and interpret agostic interactions is presented and different approaches such
as atoms in molecules (AIM), natural bonding orbitals (NBO) or the electron
localization function (ELF) are compared and put into context. A brief overview
of the history and terminology of agostic interactions is given in the
introduction and fundamental differences between alpha, beta; and other agostic
interactions are explained.

Chemical Physics