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Agostic Interactions in Early Transition‐Metal Complexes: Roles of Hyperconjugation, Dispersion, and Steric Effect
Author(s) -
Lin Xuhui,
Wu Wei,
Mo Yirong
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201900436
Subject(s) - agostic interaction , hyperconjugation , chemistry , steric effects , london dispersion force , valence bond theory , chemical physics , computational chemistry , stereochemistry , metal , molecular orbital , organic chemistry , molecule , van der waals force
The agostic interaction is a ubiquitous phenomenon in catalytic processes and transition‐metal complexes, and hyperconjugation has been well recognized as its origin. Yet, recent studies showed that either short‐range London dispersion or structural constraints could be the driving force, although proper evaluation of the role of hyperconjugation therein is needed. Herein, a simple variant of valence bond theory was employed to study a few exemplary Ti complexes with α‐ or β‐agostic interactions and interpret the agostic effect in terms of the steric effect, hyperconjugation, and dispersion. For the complexes [MeTiCl 3 (dmpe)] and [MeTiCl 3 (dhpe)] with α‐agostic interactions, hyperconjugation plays the dominant role with comparable magnitudes in both systems, but dispersion is solely responsible for the stronger agostic interaction in the former compared with the latter. For the complexes [EtTiCl 3 (dmpe)] and [EtTiCl 3 (dhpe)] with β‐agostic interactions, however, hyperconjugation and dispersion play comparable roles, and the weaker steric repulsion leads to a stronger agostic effect in the former than in the latter. Thus, the present study clarifies the variable and sensitive roles of steric, hyperconjugative, and dispersion interactions in the agostic interaction.