5 years ago

Synthesis and Reactions of [Cp*2Yb]2(μ-Me) and [Cp*2Yb]2(μ-Me)(Me) and Related Yb2(II, III) and Yb2(III, III) Compounds

Synthesis and Reactions of [Cp*2Yb]2(μ-Me) and [Cp*2Yb]2(μ-Me)(Me) and Related Yb2(II, III) and Yb2(III, III) Compounds
Marc D. Walter, Carol J. Burns, Phillip T. Matsunaga, Richard A. Andersen, Laurent Maron
A new type of synthesis, referred to as oxidative methylation, is developed for [Cp*2Yb]2(μ-X) and [Cp*2Yb]2(μ-X)(X), where X = Me, using MeCu or Cp*2VMe as the methyl transfer reagent and Cp*2Yb. The synthetic methodology is extended to other X derivatives such as the halides and BH4. Reaction of [Cp*2Yb]2(μ-Me)(Me) and H2 yields the mixed-valent hydride [Cp*2Yb]2(μ-H), which eliminates H2 on gentle heating, forming Cp*2Yb. When Cp*2VX is replaced by Cp*2TiX, 1:1 adducts based upon Ti(III,d1) are isolated. The X-ray crystal structure of [Cp*2Yb](μ-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*2Yb]2(μ-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(f13(α),(dz2)0)···H···Yb(f13(α),(dz2)1(β)), and the unpaired d electron is delocalized between the dz2 orbitals of the two Yb centers via the hydride bridge using the σ* orbital of the Yb(dz2)–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(f13(α),(dz2)0)···H···Yb(f13(α),(dz2)1(α)), also giving rise to delocalization of the d electron between the dz2 orbitals of the two Yb centers. The second spin doublet resembles the Lewis structure with an asymmetric μ-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*2YbIII fragment. Electronic energies (ΔE) computed at the DFT (B3PW91) level of theory provide insights into the thermochemistry of the formation and decomposition of [Cp*2Yb]2(μ-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*2Yb]2(μ-CH3) is ca. 60 kcal/mol more exothermic than the formation of [Cp*2Yb]2(μ-H). This difference is ascribed to enhanced intramolecular steric repulsion between the Cp*2Yb moieties in the linear Yb–H–Yb unit.

Publisher URL: http://dx.doi.org/10.1021/acs.organomet.7b00384

DOI: 10.1021/acs.organomet.7b00384

You might also like
Discover & Discuss Important Research

Keeping up-to-date with research can feel impossible, with papers being published faster than you'll ever be able to read them. That's where Researcher comes in: we're simplifying discovery and making important discussions happen. With over 19,000 sources, including peer-reviewed journals, preprints, blogs, universities, podcasts and Live events across 10 research areas, you'll never miss what's important to you. It's like social media, but better. Oh, and we should mention - it's free.

  • Download from Google Play
  • Download from App Store
  • Download from AppInChina

Researcher displays publicly available abstracts and doesn’t host any full article content. If the content is open access, we will direct clicks from the abstracts to the publisher website and display the PDF copy on our platform. Clicks to view the full text will be directed to the publisher website, where only users with subscriptions or access through their institution are able to view the full article.