Bulky Substituent Effect on Reactivity of Localized Singlet Cyclopentane‐1,3‐diyls with π‐Single Bonding (C‐π‐C) Character

Abstract

Thorough investigation of key intermediates, such as long‐lived singlet diradicals, is essential to understand the homolytic bond cleavage reactions. In this study, we evaluate the effect of bulky substituents at the meta‐position of the phenyl ring on the bond formation process in singlet 2,2‐diethoxy‐1,3‐diarylcyclopentane‐1,3‐diyls. The bulky groups have significant influence on the diradical lifetime, as such, when the triisopropylphenyl group was used, the lifetime was 45 times longer than that of the parent diradical in benzene at 293 K.

Impact of the macrocyclic structure and dynamic solvent effect on the reactivity of a localised singlet diradicaloid with π-single bonding character

“…53,54 Hence, the p-single bonding character (Cp-C) characterises Type-1 molecules because the bonding orbital c S is HOMO. 55 Recently, long-lived singlet diradicaloids S-DR2c (s 293 ¼ 23.8 ms in benzene) and S-DR2d (s 293 ¼ 9.67 ms in toluene), featuring the bulky-substituent and nitrogen-atom effects, respectively, were observed at 293 K. 56,57 Additionally, several heavy-atom analogues S-DR2e-k, including Type-2 singlet diradicaloids, have been isolated (Scheme 1). [58][59][60][61][62][63][64] Very recently, veand four-membered cyclic silicon analogues of psingle bonded species were reported.…”

1,3-Diradicals Embedded in Curved Paraphenylene Units: Singlet versus Triplet State and In-Plane Aromaticity

“…In the past decade, open-shell molecules have attracted considerable attention not only in the field of reactive intermediates but also in materials science. For example, radical-based light-emitting diodes have been developed using isolatable triaryl methyl radicals, − magnetically robust high-spin molecules have been developed using new molecular designs, , and a new bonding system, π single bonding, has emerged through research into localized diradicals. − Furthermore, the isolation of singlet diradicaloids such as Tchitchibabin derivatives has revealed their singlet fission behavior and nonlinear optical character, and these are now hot topics in π-conjugated materials. ,− To date, we have investigated the localized 1,3-diradicals DR (see Figure a), which are key intermediates in bond homolysis. − The ground-state spin multiplicity is typically controlled by the substituents at the C2 position, and the triplet ground state for DR having X = H, CH 3 can be switched to a singlet ground state by the introduction of electron-donating and electron-withdrawing substituents, for example, X = F, OR, SiR 3 (Figure a). , …”

Silicon–silicon π single bond

“…1a ). This new π single bond has recently been reported to present in singlet diradicals with π single bond character and stabilization of such singlet diradicals have been challenged 1 – 3 . On the other hand, studies on singlet diradicals consisting of heteroatoms have recently been developed 4 – 6 .…”