The structure of hexamethyltungsten, W(CH3)6, was determined by x-ray single-crystal diffraction at −163°C. The molecule has a strongly distorted trigonal prismatic structure with C3v symmetry. This irregular structure is not a result of intermolecular forces, but rather represents its true molecular structure. A similar structure, which deviates less from the ideal trigonal prismatic structure, was determined for hexamethylrhenium, Re(CH3)6. Although these structures violate the simplistic models used to predict the geometry of molecules, they are at least in part explainable by the molecular orbital model.

https://science.sciencemag.org/content/sci/271/5249/626.full.pdf

Crystal and Molecular Structures of Hexamethyltungsten and Hexamethylrhenium

Under certain circumstances, metal complexes with a formal d(0) electronic configuration may exhibit structures that violate the traditional structure models, such as the VSEPR concept or simple ionic pictures. Some examples of such behavior, such as the bent gas-phase structures of some alkaline earth dihalides, or the trigonal prismatic coordination of some early transition metal chalcogenides or pnictides, have been known for a long time. However, the number of molecular examples for "non-VSEPR" structures has increased dramatically during the past decade, in particular in the realm of organometallic chemistry. At the same time, various theoretical models have been discussed, sometimes controversially, to explain the observed, unusual structures. Many d(0) systems are important in homogeneous and heterogeneous catalysis, biocatalysis (e.g. molybdenum or tungsten enzymes), or materials science (e.g. ferroelectric perovskites or zirconia). Moreover, their electronic structure without formally nonbonding d orbitals makes them unique starting points for a general understanding of structure, bonding, and reactivity of transition metal compounds. Here we attempt to provide a comprehensive view, both of the types of deviations of d(0) and related complexes from regular coordination arrangements, and of the theoretical framework that allows their rationalization. Many computational and experimental examples are provided, with an emphasis on homoleptic mononuclear complexes. Then the factors that control the structures are discussed in detail. They are a) metal d orbital participation in sigma bonding, b) polarization of the outermost core shells, c) ligand repulsion, and d) pi bonding. Suggestions are made as to which of the factors are the dominant ones in certain situations. In heteroleptic complexes, the competition of sigma and pi bonding of the various ligands controls the structures in a complicated fashion. Some guidelines are provided that should help to better understand the interrelations. Bent's rule is of only very limited use in these types of systems, because of the paramount influence of pi bonding. Finally, computed and measured structures of multinuclear complexes are discussed, including possible consequences for the properties of bulk solids.

“Non-VSEPR” Structures and Bonding in d0 Systems

6.02 – Pyrimidines and their Benzo Derivatives

Palladium catalysed intramolecular coupling of aryl and benzylic halides and related tandem cyclisations. A simple synthesis of hippadine.

Flüchtige Metallalkoxide nach dem Konzept der Donorfunktionalisierung

/pdf/stannylation-reactions-and-palladium-catalysis-in-the-3zygatq69u.pdf

Stannylation Reactions and Palladium Catalysis in the Syntheses of Unsymmetrical Biheteroaryls.

Die IR- und Ramanspektren der monomeren Hexamethoxide des Wolframs und Molybdans sowie des ionischen [Me4Sb]+[Sb(OMe)6]− (dargestellt aus [Sb(OMe)5]2 und Me4SbOMe; Me = CH3) werden aufgenommen und der Punktgruppe C3i zugeordnet. Kraftkonstantenrechnungen fur W(OMe)6 und fur [Sb(OMe)6]− ergeben praktisch identische WO- und SbO-Valenzkraftkonstanten (2,56 N/cm), dagegen sind die ubrigen Kraftkonstanten signifikant verschieden.



Vibrational Spectra and Force Constants of W(OCH3)6, Mo(OCH3)6, and [Sb(CH3)4][Sb(OCH3)6]



The infrared and Raman spectra of the monomeric hexamethoxides of Tungsten and Molybdenum and of the ionic compound [Me4Sb]+[Sb(OMe)6]− (prepared from [Sb(OMe)5]2 and Me4SbOMe; Me = CH3) are recorded and interpreted on the basis of C3i symmetry. The force fields of W(OMe)6 and [Sb(OMe)6]− are calculated using the same basis set of force constants. Both WO- and SbO- stretching force constants are identical (2.56 N/cm), however the other parts of the valence force field are markedly different.

Schwingungsspektren und Kraftkonstanten von W(OCH3)6, Mo(OCH3)6 und [Sb(CH3)4][Sb(OCH3)6]

/pdf/the-molecular-structure-of-tungsten-hexamethoxide-w-och3-6-128sep4n03.pdf

The Molecular Structure of Tungsten Hexamethoxide, W(OCH3)6, by Gas Electron Diffraction.

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Stannylation Reactions and Palladium Catalysis in the Syntheses of Unsymmetrical Biheteroaryls.

Schwingungsspektren und Kraftkonstanten von W(OCH3)6, Mo(OCH3)6 und [Sb(CH3)4][Sb(OCH3)6]

The Molecular Structure of Tungsten Hexamethoxide, W(OCH3)6, by Gas Electron Diffraction.