Sm(II) and Yb(II) Assisted C-F Bond Activation of Monofluorinated Alkanes

Abstract

In this study, the lanthanide complexes Sm(HMDS)2 (1), Yb(HMDS)2 (2), Sm(Cp*)2 (3),
and Yb(Cp*)2 (4) were synthesized, and a new polymorph of 2 was identified via single-
crystal X-ray diffraction (sc-XRD). Additionally, the previously unreported Yb(III) compound [YbI2(OPPh3)4]I was discovered as a probable disproportionation product of
YbI2(OPPh3)4 and characterized via 31P{1H} NMR spectroscopy and sc-XRD. The complexes were evaluated for their efficacy in the reductive defluorination of 1-fluorooctane.
The Cp* complexes 3 and 4 exhibited superior activity, achieving 100% conversion under
the same conditions where the HMDS complexes 1 and 2 reached 87% and 60% conversion, respectively. Product distribution analysis revealed that 1 and 2 exclusively formed
noctane, while 3 and 4 facilitated radical recombination and disproportionation, yielding
nhexadecane, 1-octene, and (E)-2-octene, indicative of higher radical concentrations in
the reaction mix. The addition of THF to the reaction with complex 4 increased the fraction of formed nhexadecane, suggesting radical-stabilizing properties of THF. Attempts
at lanthanide-mediated reductive borylation and silylation were conducted, with only
Sm(Cp*)2 (3) + B2Pin2 displaying tentative evidence for octyl-Bpin formation. Kinetic
measurements confirmed ab inito predicted activation barriers, showing a 3.5-fold higher
initial reaction rate for 1 compared to 2. 19F{1H} NMR monitoring revealed Sm-F
coupling for 1 at ambient temperature, decreasing with higher temperatures, indicating
substrate pre-coordination. Despite multiple crystallization attempts, no Ln(III) fluoride
complexes were isolated

Popular Abstract

This study explores how particular metal-containing compounds, called lanthanide complexes, can break strong carbon-fluorine (C-F) bonds. Four different complexes - two
based on samarium (Sm) and two on ytterbium (Yb) - were synthesized and tested for
their ability to remove fluorine from an organic molecule, 1-fluorooctane.
The results showed that some complexes were much more effective than others. Two of
them, Sm(Cp*)2 and Yb(Cp*)2, completely removed fluorine under semi-mild conditions,
while the others were slower. The breakdown process also produced different organic
molecules, suggesting that some complexes create a higher concentration of reactive fragments (radicals) in the process than others. Interestingly, adding a common solvent, THF, changed the types of products formed, hinting that it helps stabilize these radicals rather than just donating hydrogen, as previously assumed. In an effort to expand this chemistry, additional experiments attempted to attach new elements like boron and silicon to the carbon chain after removing fluorine. However, only one reaction showed weak evidence of success, leaving this as an open challenge for future research. To better understand how these reactions work, kinetic measurements confirmed theoretical predictions about reaction speeds and energy barriers. Additionally, unique interactions between samarium and fluorine were observed at room temperature, suggesting the molecule first binds to the metal before breaking apart. Despite attempts, the expected metal-fluoride byproducts could not be isolated. These findings contribute to a deeper understanding of how lanthanides can be used to break C-F bonds, a key step toward new applications in
recycling fluorinated materials and developing novel chemical transformations.

• author: Wurm, Frerik
• supervisor: Vasudevan Subramaniyan
• organization: Department of Chemistry
• course: KEMP30 20242
• year: 2025
• type: L3 - Miscellaneous, Projetcs etc.
• subject: Chemistry
• keywords: lanthanide complexes, reductive defluorination, carbon-fluorine bond activation, organolanthanide chemistry, radical reactions, kinetic analysis, fluorinated organic compounds, reaction mechanism
• language: English
• id: 9185422
• date added to LUP: 2025-03-03 09:16:58
• date last changed: 2025-03-03 09:16:58