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Issue 7, 2020
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Equilibria and mesomerism/valence tautomerism of group 4 metallocene complexes

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Abstract

In this account, examples of the influence of equilibrium and mesomerism/valence tautomerism on reactions of selected group 4 metallocene complexes will be discussed. Complexes of bis(trimethylsilyl)acetylene Me3SiC2SiMe3 (mono-functional alkynes: C[triple bond, length as m-dash]C) in Cp′2M(η2-Me3SiC2SiMe3) (Cp′ = substituted η5-cyclopentadienyl), of α-di-Ph2P- (hetero-tri-functional: P, C[triple bond, length as m-dash]C, P) in Cp′2M(η2-Ph2C2PPh2), and of α-mono-SiH- (hetero-bi-functional: C[triple bond, length as m-dash]C, SiH) and α-di-SiH-substituted alkynes (hetero-tri-functional: SiH, C[triple bond, length as m-dash]C, SiH) in Cp′2M(η2-Me3SiC2SiMe2H) and Cp′2M(η2-HMe2SiC2SiMe2H), respectively, were considered. Additionally, unusual all-C-metallacycles like metallacyclopentynes Cp′2M[η2-C(R2)–C2–C(R2)–] (formed by coordination of tri-functional trienes: C[double bond, length as m-dash]C, C[double bond, length as m-dash]C, C[double bond, length as m-dash]C), five-membered metallacycloallenes Cp′2M[η2-C(R)[double bond, length as m-dash]C[double bond, length as m-dash]C(R)–C(R2)–] (formed by coordination of bi-functional enynes: C[double bond, length as m-dash]C, C[triple bond, length as m-dash]C), metallacyclocumulenes Cp′2M[η2-C(R)[double bond, length as m-dash]C[double bond, length as m-dash]C[double bond, length as m-dash]C(R)–] (formed by coordination of bi-functional diynes: C[triple bond, length as m-dash]C, C[triple bond, length as m-dash]C), and seven-membered metallacyclocumulenes Cp′2M[η2-C(R)[double bond, length as m-dash]C(C2R)–C(R)[double bond, length as m-dash]C[double bond, length as m-dash]C[double bond, length as m-dash]C(R)–] (formed by coordination of two bi-functional diynes: C[triple bond, length as m-dash]C, C[triple bond, length as m-dash]C), with M = Ti, Zr, and Hf were selected as examples for considerations of equilibrium and mesomerism/valence tautomerism. On the basis of spectroscopic investigations, their molecular structures and selected calculations, it is discussed how the different interpretations of the equilibrium and mesomerism/valence tautomerism are in line with observed reactivity patterns.

Graphical abstract: Equilibria and mesomerism/valence tautomerism of group 4 metallocene complexes

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Article information


Submitted
19 Nov 2019
First published
18 Mar 2020

Chem. Soc. Rev., 2020,49, 2119-2139
Article type
Review Article

Equilibria and mesomerism/valence tautomerism of group 4 metallocene complexes

U. Rosenthal, Chem. Soc. Rev., 2020, 49, 2119
DOI: 10.1039/C9CS00637K

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