Skip to Main content Skip to Navigation
Journal articles

Synthesis and Reactions of [Cp*Yb-2](2)(mu-Me) and [Cp*Yb-2](2)(mu-Me)(Me) and Related Yb-2(II, III) and Yb-2(III, III) Compounds

Abstract : A new type of synthesis, referred to as oxidative methylation, is developed for [Cp*Yb-2](2)(mu-X) and [Cp*Yb-2](2)(mu-X)(X), where X = Me, using MeCu or Cp*2VMe as the methyl transfer reagent and Cp*Yb-2. The synthetic methodology is extended to other X derivatives such as the halides and BH4. Reaction of [Cp*Yb-2](2)(mu-Me)(Me) and H-2 yields the mixed-valent hydride [Cp*Yb-2](2)(mu-H), which eliminates H-2 on gentle heating, forming Cp*Yb-2. When Cp*2VX is replaced by Cp*2TiX, 1:1 adducts based upon Ti(III,d(1)) are isolated. The X-ray crystal structure of [Cp*Yb-2](mu-Me)[TiCp*(2)] shows that the methyl group bridges the two different decamethylmetallocene fragments in a near-linear fashion, a geometry that is likely to resemble the transition state of the single-electron-transfer precursor complex. A CASSCF computational study on the mixed-valent hydride [Cp*Yb-2](2)(mu-H) shows that the ground state is a spin doublet in which the hydride forms a symmetric bridge to both Yb atoms. The three spins forming the ground-state doublet are aligned as Yb(f(13)(alpha),(d(z2))(0))center dot center dot center dot H center dot center dot center dot Yb(f(13)(alpha),(d(z2))(1)(beta)), and the unpaired d electron is delocalized between the d(z2) orbitals of the two Yb centers via the hydride bridge using the sigma* orbital of the Yb(d(z2))-H bond. The first excited state lies 0.09 eV (725 cm(-1)) higher in energy and is a spin quartet in which the three spins are aligned as Yb(f(13)(alpha),(d(z2))(0))center dot center dot center dot H center dot center dot center dot Yb(f(13)(alpha),(d(z2))(1)(alpha)), also giving rise to delocalization of the d electron between the d(z2) orbitals of the two Yb centers. The second spin doublet resembles the Lewis structure with an asymmetric mu-H bridge in which the Yb(II) metallocene has a closed-shell electronic configuration and is approximately 0.15 eV (1210 cm(-1)) higher in energy than the ground-state delocalized open-shell doublet. The electronic structure of the mixed-valent methyl is closely related to that of the hydride, but the methyl group is localized on the Cp*Yb-2(III) fragment. Electronic energies (Delta E) computed at the DFT (B3PW91) level of theory provide insights into the thermochemistry of the formation and decomposition of [Cp*Yb-2](2)(mu-H). The BDE for Yb-H is ca. 15 kcal/mol stronger than that for the corresponding Yb-Me in the monomeric metallocenes. In contrast, formation of [Cp*Yb-2](2)(mu-CH3) is ca. 60 kcal/mol more exothermic than the formation of [Cp*Yb-2](2)(mu-H). This difference is ascribed to enhanced intramolecular steric repulsion between the Cp*Yb-2 moieties in the linear Yb-H-Yb unit.
Document type :
Journal articles
Complete list of metadatas

https://hal.insa-toulouse.fr/hal-01961151
Contributor : Insa Toulouse Scd <>
Submitted on : Wednesday, December 19, 2018 - 5:16:24 PM
Last modification on : Tuesday, March 3, 2020 - 11:40:04 AM

Identifiers

  • HAL Id : hal-01961151, version 1

Citation

Marc D. Walter, Philip T. Matsunaga, Carol J. Burns, Laurent Maron, Richard A. Andersen. Synthesis and Reactions of [Cp*Yb-2](2)(mu-Me) and [Cp*Yb-2](2)(mu-Me)(Me) and Related Yb-2(II, III) and Yb-2(III, III) Compounds. Organometallics, 2017, 36 (23), pp.4564--4578. ⟨hal-01961151⟩

Share

Metrics

Record views

25