Mechanisms of dihydrogen activation by zirconocene alkyl and hydride derivatives : A molecular orbital analysis of a 'direct hydrogen transfer' reaction mode

Brintzinger, Hans-Herbert

Mechanisms of dihydrogen activation by zirconocene alkyl and hydride derivatives : A molecular orbital analysis of a 'direct hydrogen transfer' reaction mode

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Brintzinger_239141.pdfGröße: 456.19 KBDownloads: 292

Datum

1979

Open Access-Veröffentlichung

Open Access Green

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Chemie

Publikationstyp

Zeitschriftenartikel

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Published

Erschienen in

Journal of Organometallic Chemistry. 1979, 171(3), pp. 337-344. ISSN 0022-328X. Available under: doi: 10.1016/S0022-328X(00)82657-1

Zusammenfassung

The formation of an adduct between a dihydrogen and a d⁰ species of the general type (C₅R₅)₂Zr(R′)₂ (R,R′ = H or CH₃) is suggested to involve a process analogous to that in CO adduct formation, and is studied by an extended Hückel molecular orbital analysis. Back donation into σ* H₂ orbitals arises from high-lying M-R′ bonding orbitals and determines the stability of alternative adduct geometries. Two isomeric H₂ adducts can interconvert by an intramolecular hydrogen shift. With D₂, this reaction sequence leads to hydrogen isotope exchange. The transition state of this reaction mode contains a three-centre (H⋯H⋯H)⁻ ligand configuration with bonding properties similar to those of an allyl ligand; it does not involve an oxidative change in the charge on the metal nor generation of a positively charged, protonic hydrogen species by heterolytic H₂ cleavage. The term ‘direct hydrogen transfer’ is proposed for this type of elementary reaction. For H₂-induced alkane elimination from group IV metallocene alkyl derivatives, an analogous reaction mechanism, involving formation of a H₂ adduct and a subsequent intramolecular hydrogen shift toward the alkyl ligand, is predicted to proceed with moderate activation energies.

Fachgebiet (DDC)

540 Chemie

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ISO 690

BRINTZINGER, Hans-Herbert, 1979. Mechanisms of dihydrogen activation by zirconocene alkyl and hydride derivatives : A molecular orbital analysis of a 'direct hydrogen transfer' reaction mode. In: Journal of Organometallic Chemistry. 1979, 171(3), pp. 337-344. ISSN 0022-328X. Available under: doi: 10.1016/S0022-328X(00)82657-1

BibTex

@article{Brintzinger1979Mecha-23914,
  year={1979},
  doi={10.1016/S0022-328X(00)82657-1},
  title={Mechanisms of dihydrogen activation by zirconocene alkyl and hydride derivatives : A molecular orbital analysis of a 'direct hydrogen transfer' reaction mode},
  number={3},
  volume={171},
  issn={0022-328X},
  journal={Journal of Organometallic Chemistry},
  pages={337--344},
  author={Brintzinger, Hans-Herbert}
}

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    <dcterms:abstract xml:lang="eng">The formation of an adduct between a dihydrogen and a d&lt;sup&gt;0&lt;/sup&gt; species of the general type (C&lt;sub&gt;5&lt;/sub&gt;R&lt;sub&gt;5&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;Zr(R′)&lt;sub&gt;2&lt;/sub&gt; (R,R′ = H or CH&lt;sub&gt;3&lt;/sub&gt;) is suggested to involve a process analogous to that in CO adduct formation, and is studied by an extended Hückel molecular orbital analysis. Back donation into σ* H&lt;sub&gt;2&lt;/sub&gt; orbitals arises from high-lying M-R′ bonding orbitals and determines the stability of alternative adduct geometries. Two isomeric H&lt;sub&gt;2&lt;/sub&gt; adducts can interconvert by an intramolecular hydrogen shift. With D&lt;sub&gt;2&lt;/sub&gt;, this reaction sequence leads to hydrogen isotope exchange. The transition state of this reaction mode contains a three-centre (H⋯H⋯H)&lt;sup&gt;−&lt;/sup&gt; ligand configuration with bonding properties similar to those of an allyl ligand; it does not involve an oxidative change in the charge on the metal nor generation of a positively charged, protonic hydrogen species by heterolytic H&lt;sub&gt;2&lt;/sub&gt; cleavage. The term ‘direct hydrogen transfer’ is proposed for this type of elementary reaction. For H&lt;sub&gt;2&lt;/sub&gt;-induced alkane elimination from group IV metallocene alkyl derivatives, an analogous reaction mechanism, involving formation of a H&lt;sub&gt;2&lt;/sub&gt; adduct and a subsequent intramolecular hydrogen shift toward the alkyl ligand, is predicted to proceed with moderate activation energies.</dcterms:abstract>
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