Agostic interactions other ligands

Electron density calculations have been carried out on Gp2ScR (R=H, Me, Et, Prn, vinyl, acetylide). Geometry optimizations revealed an agostic interaction for R= Et, whereas Me and Pr are bonded to the metal center without agostic interactions. Other density functional studies have been carried out on the complexes Cp2LnCl and Cp2LnX(THF) (Ln = La-Lu X = F, Cl, Br, I). In these mixed ligand complexes, Ln-Cp and Ln-THF bonds are... 

In hypersilyl sodium and potassium both, infra- and intermolecular M "H-C agostic interactions occur, leading to short M -C distances. Interactions of this type were found in many other alkali metal compounds - a survey is given in reference [5]. In the hypersilyl lithiiun dimers only short znframolecular M--H-C contacts are observed (M "C 239, 245 pm), combined with a significant lengthening of the involved Si-C bonds (191 pm) and a pronounced tilting of the hypersilyl ligands (Fig. 3). 

This convention may also be used for ligands in which o-bonds are coordinated in a side-on fashion, such as the H-H bond in complexes of dihydrogen (i.e. r 2-H2)5 or the saturated C-H bonds in agostic interactions.6 The p symbol and locants for agostic interactions are placed separately from other locants at the end of the ligand name. In Example 30 the agostic bond is denoted by a half arrow. 

Other examples of C-H H-M short contacts [44] were found in iridium complexes, and the competition between agostic interactions and hydrogen bonds was tested by QMMM calculations for several R groups hanging from an orthometallated benzoquinoline ligand. The agostic structure is favored for t-Bu, but the hydrogen bond is preferred by isopropyl [44b]. 

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