Observation of a thermally accessible triplet state resulting from rotation around a main-group π bond

Arseni Kostenko; Boris Tumanskii; Miriam Karni; Shigeyoshi Inoue; Masaaki Ichinohe; Akira Sekiguchi; Yitzhak Apeloig

doi:10.1002/anie.201506291

Observation of a thermally accessible triplet state resulting from rotation around a main-group π bond

Angew Chem Int Ed Engl. 2015 Oct 5;54(41):12144-8. doi: 10.1002/anie.201506291. Epub 2015 Aug 20.

Authors

Arseni Kostenko¹, Boris Tumanskii¹, Miriam Karni¹, Shigeyoshi Inoue², Masaaki Ichinohe², Akira Sekiguchi³, Yitzhak Apeloig⁴

Affiliations

¹ Schulich Faculty of Chemistry and Lise Meitner-Minerva Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, Haifa 32000 (Israel).
² Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571 (Japan).
³ Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571 (Japan). sekiguch@chem.tsukuba.ac.jp.
⁴ Schulich Faculty of Chemistry and Lise Meitner-Minerva Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, Haifa 32000 (Israel). apeloig@technion.ac.il.

PMID: 26297814
DOI: 10.1002/anie.201506291

Abstract

We report the first direct spectroscopic observation by electron paramagnetic resonance (EPR) spectroscopy of a triplet diradical that is formed in a thermally induced rotation around a main-group π bond, that is, the SiSi double bond of tetrakis(di-tert-butylmethylsilyl)disilene (1). The highly twisted ground-state geometry of singlet 1 allows access to the perpendicular triplet diradical 2 at moderate temperatures of 350-410 K. DFT-calculated zero-field splitting (ZFS) parameters of 2 accurately reproduce the experimentally observed half-field transition. Experiment and theory suggest a thermal equilibrium between 1 and 2 with a very low singlet-triplet energy gap of only 7.3 kcal mol(-1) .

Keywords: EPR spectroscopy; density functional calculations; diradicals; disilenes; zero-field splitting parameters.

Publication types

Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

Electron Spin Resonance Spectroscopy
Models, Molecular
Quantum Theory
Silicon Compounds / chemistry*
Temperature
Thermodynamics

Substances

Silicon Compounds