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Valence Charge Concentrations, Electron Delocalization and β‐Agostic Bonding in d 0 Metal Alkyl Complexes
Author(s) -
Scherer Wolfgang,
Sirsch Peter,
Shorokhov Dmitry,
Tafipolsky Maxim,
McGrady G. Sean,
Gullo Emanuel
Publication year - 2003
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.200304909
Subject(s) - agostic interaction , delocalized electron , alkyl , chemistry , crystallography , metal , valence electron , ligand (biochemistry) , valence (chemistry) , atom (system on chip) , covalent bond , density functional theory , electron localization function , computational chemistry , electron , physics , organic chemistry , biochemistry , receptor , quantum mechanics , computer science , embedded system
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 β‐agostic interaction in d 0 metal alkyl complexes, which is driven by delocalization of the MC bonding electrons. Topological analysis of theoretical and experimental charge densities reveals LICCs at the metal atom, and indicates delocalization of the MC valence electrons over the alkyl fragment, with depletion of the metal‐directed charge concentration (CC) at the α‐carbon atom, and a characteristic ellipticity profile for the C α C β bond. These ellipticity profiles and the magnitude of the CC values at C α and C β 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 CH activation in agostic complexes.