Using soft X-ray absorption spectroscopy to evaluate the electronic structures of sp2-hybridized carbons in organic solvents

Abstract

The reactivity of an organic compound is often discussed in relation to the bond length at the reaction site. However, obtaining such information in organic solvents, where most organic reactions occur, remains a demanding task. Here, we analyze the electronic structures of organic molecules containing sp ² carbons in organic solvents using soft X-ray absorption spectroscopy (Soft-XAS-OS). By determining the energy thresholds of representative organic solvents, we confirmed that the electronic states of sp ² carbons can be distinguished from solvent absorption. Soft-XAS-OS was applied to study the Hiyama cross-coupling reaction. The observed XAS spectra of arylsilanes in organic solvents were rationalized in terms of C-Si bond elongation through the inner-shell calculations combined with molecular dynamics simulations. The reactive glycolderived silicate Ph-Si(OCH2CH2O)2 exhibited longer C-Si bonds in solution than the less reactive Ph-Si(OMe)3. These findings demonstrate that Soft-XAS-OS, combined with inner-shell calculations, provides a powerful method for probing electronic structures and gaining insights into the bond lengths related to sp² carbons in organic solvents.