Principles and Applications of Density Functional Theory in Inorganic Chemistry II
It is difficult to overestimate the impact that density functional theory has had on computational quantum chemistry over the last two decades. Indeed, this period has seen it grow from little more than a theoreticalcuriosity to become a central tool in t
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Agostic Interactions from a Computational Perspective: One Name, Many Interpretations Eric Clot · Odile Eisenstein (*) Laboratoire de Structure et Dynamique des Systmes Molculaires et Solides (UMR 5636), cc14, Universit Montpellier 2, 34095 Montpellier Cedex 05, France [email protected]
1 1.1 1.2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Definition of the Agostic Interaction . . . . . . . . . . . . . . . . . . . . . . . Focus and Limitations of this Review. . . . . . . . . . . . . . . . . . . . . . .
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2 2.1 2.2
The C-H Agostic Interaction, from Early Studies to Recent Interpretations . The a-Agostic Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The b-Agostic Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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The Agostic C-H Bond with a Non-Transition Metal Centre. . . . . . . . . .
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4 4.1 4.2
X-H Agostic Bonds with X Different from C . . . . . . . . . . . . . . . . . . The B-H Agostic Bond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Si-H Agostic Bond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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5 5.1 5.2 5.3
X-Y Agostic with Y Different from H . The C-C Agostic Interaction. . . . . . . The Si-C Agostic Interaction . . . . . . X-Y Agostic with Y Bearing Lone Pairs .
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6 6.1 6.2 6.3
The High Sensitivity of the C-H Agostic Interaction to the Nature of the Molecule. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Energetic Magnitude of the Agostic Interaction . . . . . . . . . The Steric Influence of the Ligands . . . . . . . . . . . . . . . . . . . The Agostic Interaction: One Weak Interaction Among Other Ones.
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Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Abstract The agostic bond defines an intramolecular interaction where a s bond is geometrically close to an electron deficient centre (often a transition metal). The computational studies on this energetically weak interaction are reviewed and discussed. Various types of s bonds have been considered (C-H, C-C, Si-H, Si-C, B-H). It is suggested that a C-X bond in which X carries a lone pair should preferably not be viewed as agostic. The factors that contribute to his occurrence are discussed. In particular, the agostic interaction is very sensitive to steric effects. Explanations based on molecular orbital analysis, electron delocalization and topological analysis of the electron density are presented. Keywords Agostic interaction · Weak interaction · Bond activation · Computational studies · DFT · QM/MM calculations · Molecular orbitals · Topological analysis · Steric effects
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