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《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(34):10317-10321
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, E ST, 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. 相似文献
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