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. 2017 Aug 14;56(34):10183-10187.
doi: 10.1002/anie.201705228. Epub 2017 Jul 3.

Spectroscopic Observation of the Triplet Diradical State of a Cyclobutadiene

Arseni Kostenko  1 , Boris Tumanskii  1 , Yuzuru Kobayashi  2 , Masaaki Nakamoto  2 , Akira Sekiguchi  2   3 , Yitzhak Apeloig  1
Affiliations

Spectroscopic Observation of the Triplet Diradical State of a Cyclobutadiene

Arseni Kostenko et al. Angew Chem Int Ed Engl. .

Erratum in

Abstract

Tetrakis(trimethylsilyl)cyclobuta-1,3-diene (1) was subjected to a temperature-dependent EPR study to allow the first spectroscopic observation of a triplet diradical state of a cyclobutadiene (2). From the temperature dependent EPR absorption area we derive a singlet→triplet (1→2) energy gap, EST , of 13.9 kcal mol-1 , in agreement with calculated values. The zero-field splitting parameters D=0.171 cm-1 , E=0 cm-1 are accurately reproduced by DFT calculations. The triplet diradical 2 is thermally accessible at moderate temperatures. It is not an intermediate in the thermal cycloreversion of cyclobutadiene to two acetylene molecules.

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

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