Characterization of agostic interactions in theory and computation

Abstract

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.Comment: 24 pages, 10 figures, 109 references. Submitted to Coordination Chemistry Review

Electrochemical and Computational Study of Tungsten(0) Ferrocene Complexes: Observation of the Mono-Oxidized Tungsten(0) Ferrocenium Species and Intramolecular Electronic Interactions

“…Moreover, the computed value of 0.045 e•Å -3 for the electron density at the bond critical point, is in the range expected for CH agostic interactions. 36 The structure of this species resembles that found for oxidised products of related chromium (0) carbene complexes upon 2-electron oxidation of the transition metal. 11 This peculiar bonding situation seems to be general for oxidized products of Fischer carbene complexes regardless of the transition metal involved and it implies the normal carbene structure is not retained after oxidation.…”

Substituent Effects on the Electrochemical, Spectroscopic, and Structural Properties of Fischer Mono- and Biscarbene Complexes of Chromium(0)

“…Moreover, the computed value of 0.035 e.Å -3 for the electron density at the bond critical point, is in the range expected for CH agostic interactions. 37 This is further supported by the NBO method which locates a stabilizing electronic donation from the doubly occupied σ(C-H) molecular orbital to the vacant d atomic orbital of the chromium (associated second-order perturbation energy of -36.7 kcal/mol, see Figure 9b). The presence of the vacant orbital is, of course, a direct consequence of the oxidation process which eliminates the two electrons present in the HOMO of 3a (located in the chromium atom).…”

Strength of Si–H ⋯ B charge-inverted hydrogen bonds in 1-silacyclopent-2-enes and 1-silacyclohex-2-enes

“…Bonding properties of the Si-H· · · Y bridge are well known [5][6][7][8][9]. For example, in case of Y being a transition metal, this interaction is called an agostic bond [10][11][12][13] or a σ interaction [12][13][14][15][16][17] depending on a specific situation, whereas if Y is an electron-deficient element (as, for example, boron), this type of interaction was called a "charge-inverted hydrogen bond" (CIHB) [11][12][13][18][19][20][21][22][23][24][25].…”