In this paper we describe a range of model d(0) metal ethyl compounds and related complexes, studied by DFT calculations and high resolution X-ray diffraction. The concept of ligand-opposed charge concentrations (LOCCs) for d(0) metal complexes is extended to include both cis-and trans-ligand-induced charge concentrations (LICCs) at the metal, which arise as a natural consequence of covalent metal-ligand bond formation in transition metal alkyl complexes. The interplay between locally induced sites of increased Lewis acidity and an ethyl ligand is crucial to the development of a beta-agostic interaction in d(0) metal alkyl complexes, which is driven by delocalization of the M-C bonding electrons. Topological analysis of theoretical and experimental charge densities reveals LICCs at the metal atom, and indicates delocalization of the M-C valence electrons over the alkyl fragment, with depletion of the metal-directed charge concentration (CC) at the alpha-carbon atom, and a characteristic ellipticity profile for the C(alpha)-C(beta) bond. These ellipticity profiles and the magnitude of the CC values at C(alpha) and C(beta) provide experimentally observable criteria for assessing quantitatively the extent of delocalization, with excellent agreement between experiment and theory. Finally, a concept is proposed which promises systematic control of the extent of C-H activation in agostic complexes.
The structure, energetics, and electron density in the inclusion complex of He in adamantane, C10H16, have been studied by density functional theory calculations at the B3LYP6-311++G(2p,2d) level. Topological analysis of the electron density shows that the He atom is connected to the four tertiary tC atoms in the cage by atomic interaction lines with (3,-1) critical points. The calculated dissociation energy of the complex He@adamantane(g)=adamantane(g) + He(g) of DeltaE=-645 kJ mol(-1) nevertheless shows that the He-tC interactions are antibonding.
In this paper we present the results of density functional theory (DFT) calculations on the ethyl ligand and some related organic moieties; we then proceed to consider a range of alkyllithium complexes studied by DFT calculations and high‐resolution X‐ray and neutron diffraction. Topological analysis of the charge density is used to follow changes in the electronic structure of the organic fragment. The charge concentrations (CCs) in the valence shell at the α and β atoms reveal faithfully the delocalization of the lone pair at the Cα atom or of the Li−C bonding electrons. Negative hyperconjugation is thus shown to arise from delocalization of the lone pair or the Li−C bonding electrons over the alkyl fragment, with depletion of the metal‐directed charge concentration at Cα, and characteristic ellipticity profiles for the bonds involved in hyperconjugative delocalization. In the case of so‐called lithium agostic complexes, we show that close Li⋅⋅⋅H contacts are a consequence of this delocalization and further secondary interactions, with Li⋅⋅⋅H−C agostic interactions, playing only a minor role. The ellipticity profiles and the magnitude of the CCs at Cα provide a quantitative measure of the extent of delocalization, and show excellent agreement between experiment and theory.
Steric factors govern the formation of half-sandwich complexes (C5Me4R)Ln[N(SiHMe2)2]2 according to acid-base reactions utilising Ln[N(SiHMe2)2)3(thf)2 and substituted cyclopentadienes. Subsequent trimethylaluminium-promoted silylamide elimination produces the first half-sandwich bis(tetramethylaluminate) complexes (C5Me4R)Ln(AlMe4)2.
Combined experimental and theoretical charge density studies of the complex [Ni(g 2 -C 2 H 4 )dbpe] (dbpe = Bu t 2 PCH 2 CH 2 PBu t 2 ), 1, reveal how the location and magnitude of charge concentrations in the valence shell of the metal atom influence the rand p-components of the metal-olefin interaction.
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