Premium
Stable Oxindolyl‐Based Analogues of Chichibabin's and Müller's Hydrocarbons
Author(s) -
Wang Jian,
Xu Xingdong,
Phan Hoa,
Herng Tun Seng,
Gopalakrishna Tullimilli Y.,
Li Guangwu,
Ding Jun,
Wu Jishan
Publication year - 2017
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201708612
Subject(s) - diradical , singlet state , isomerization , chemistry , paramagnetism , crystallography , photochemistry , catalysis , organic chemistry , atomic physics , physics , condensed matter physics , excited state
Chichibabin's and Müller's hydrocarbons are classical open‐shell singlet diradicaloids but they are highly reactive. Herein we report the successful synthesis of their respective stable analogues, OxR‐2 and OxR‐3 , based on the newly developed oxindolyl radical. X‐ray crystallographic analysis on OxR‐2 reveals a planar quinoidal backbone similar to Chichibabin's hydrocarbon, in accordance with its small diradical character (y 0 =11.1 %) and large singlet–triplet gap (ΔE S‐T =−10.8 kcal mol −1 ). Variable‐temperature NMR studies on OxR‐2 disclose a slow cis/trans isomerization process in solution through a diradical transition state, with a moderate energy barrier (ΔG ≠ 298K =15–16 kcal mol −1 ). OxR‐3 exhibits a much larger diradical character (y 0 =80.6 %) and a smaller singlet–triplet gap (ΔE S‐T =−3.5 kcal mol −1 ), and thus can be easily populated to paramagnetic triplet diradical. Our studies provide a new type of stable carbon‐centered monoradical and diradicaloid.