Origin of β-agostic interaction in d0 transition metal alkyl complexes: Influence of ligands

Publication date: Available online 3 February 2018 Source:Journal of Organometallic Chemistry Author(s): Shyama Ramakrishnan, Eluvathingal D. Jemmis Classical picture of agostic interaction involves a three-center two-electron interaction where the metal center has valence electron count less than sixteen. Though unsaturation on metal center is a necessary condition, it is not sufficient to show agostic interaction. For example, TiEtCl3 and its diphosphine adduct TiEtCl3(dmpe) have d0-metal center and the electron count is far less from 18 electrons for both. But TiEtCl3 shows no agostic interaction while TiEtCl3(dmpe) has an agostic interaction. An explanation based on negative hyperconjugation is put forward to explain the special case of C-H activation using d0-metal centers, which is also not sufficient. On electronic and steric grounds, TiEtCl3, rather than TiEtCl3(dmpe), is expected to exhibit agostic interaction, contrary to the experimental observation. If a molecule possesses vacant orbital in the plane of the M-Cα-Cβ-H fragment with appropriate energy, agostic interaction follows. How the nature and arrangement of the ligands around the metal center influence the origin of β-agostic interaction in d0 transition metal alkyl complexes is described in this paper. Octahedral type of arrangement of ligands around metal center in TiEtCl3(dmpe) and the π* orbitals of CN and CF3 group help TiEt(CN)3 and TiEt(CF3)3 to be agostic. Graphical abstract

Source: Journal of Organometallic Chemistry - February 3, 2018 Category: Chemistry Source Type: research