Helicenes are ortho-annelated polycyclic aromatic molecules with nonplanar helical conjugation of the p-electron system. [1] These aromatic molecules have attracted special attention not only because of the nonplanarity of the p-conjugated skeleton but also because of their inherent helical chirality. Recent developments in helicene chemistry have focused on the synthesis and optical resolution of new helicene derivatives [2] as well as on asymmetric catalysts, [3] molecular recognition, [4] and chiroptical functionalities. [5,6] However, almost all of the helicene derivatives investigated so far are intrinsically closed-shell electronic systems except for a few examples. [7] Thus, the chemistry of open-shell helicenes has been little explored in the past; to our knowledge there have been no experimental studies on helicene-based nonplanar chiral neutral p-radical systems. [8] As stable open-shell molecular systems possessing chirality, a number of nitroxide-based chiral neutral radical derivatives have been synthesized and characterized. [9] These systems were constructed by introducing a substituent having one or more asymmetric carbon atoms to an achiral nitroxide radical skeleton based on, for example, pyrrolidine-1-oxyl and a-nitronylnitroxide. By taking advantage of the localized unpaired electronic spin on the NÀO moiety, chiral molecular magnets and paramagnetic organic chiral liquid crystals have extensively been implemented. [9b, 10] In contrast to the nitroxide radicals, in phenalenyl (PLY in Figure 1), a planar neutral hydrocarbon p-radical, the electronic spin is extensively delocalized over the whole molec-ular skeleton. [11] As a consequence, phenalenyl derivatives exhibit unique physical properties and functionalities different from the those of spin-localized neutral radicals such as nitroxide derivatives. [11,12] Furthermore, our recent study revealed that the highly delocalized electronic structure inherent in phenalenyl also appears in a curved phenalenyl system with a corannulene substructure (Cor-PLY, Figure 1). [13,14] Cor-PLY is the first nonplanar phenalenyl derivative in the half-century-old phenalenyl chemistry.These studies have inspired us to design nonplanar pconjugated chiral phenalenyl radicals based on helicene. [11b] The chiral neutral p-radical is intriguing not only because of the spin delocalization in the three-dimensional (3D) helical p-conjugated network but also because of optical magnetic properties attributable to the combination of helicene chirality and delocalized electronic spin. Here we report the synthesis, electronic-spin structure, and optical properties of chiral diazaphenalenyl 1 (Figure 1), [15] in which a benzene ring is fused to a nitrogen-containing [4]helicene-type structure. Thanks to two terminal methoxy groups and three tert-butyl groups, radical 1 exhibits high configurational and chemical stability, enabling us to experimentally characterize both chiral and racemic species of 1 with the help of theoretical calculations. Solution-phase ESR and EN...

Radically active: A redox-active air-stable neutral π radical (1(·)) with three dicyanomethylene groups introduced with threefold symmetry into a triangulene π skeleton instead of the oxygen atoms of TOT(·) was designed, synthesized, and characterized (see figure). The enhanced electron-accepting ability and extended π-electronic system of this chemical modification gave an extremely small SOMO-LUMO gap and significantly lowered the frontier orbital energies, leading to the remarkable increase in the redox stages.

Palladium‐catalyzed cross‐coupling of acid‐ and base‐unstable heteroatom‐functionalized organosilanes and C(sp2)X electrophiles such as aryl and alkenyl (pseudo)halides has been extensively studied. In contrast, little is known about the coupling between unactivated alkenyltrialkylsilanes and C(sp3)X electrophiles. Herein, the copper(I)‐promoted coupling of chromatographically stable alkenylbenzyldimethylsilanes with unreactive alkyl halides as well as allyl and benzyl halides is described. The reaction proceeds in the presence of CuI‐P(OEt)3 and Bu4NF⋅(tBuOH)4 to produce stereodefined di‐ and trisubstituted alkenes with complete retention of configuration.

Ein neuer Dreh bei einem alten System: Die neutralen Titelradikale wurden erstmals synthetisiert und charakterisiert. Dank der beiden terminalen Methoxygruppen und der drei tert‐Butylgruppen sind die chiralen Radikale konfigurativ und chemisch stabil. Das dreidimensionale π‐Elektronennetzwerk weist eine ausgeprägte Spindelokalisierung auf, und charakteristische CD‐Eigenschaften werden mit der Chiralität der Heliceneinheit erklärt (siehe Bild).

A triangulene-based C2-symmetric 33 π-conjugated stable neutral π-radical, 2(·), which possesses two dicyanomethylene groups and one oxo group, has been designed, synthesized, and isolated as an analogue of tris(dicyanomethylene) derivative 1(·) and trioxo derivative TOT(·) with C3 symmetry. Effects of molecular-symmetry reduction and electron-accepting substituents on this fused polycyclic neutral π-radical system were studied in terms of their molecular structure, electronic-spin structure, and electrochemical and optical properties with the help of theoretical calculations. Interestingly, this system (2(·)) has a four-stage redox ability, like TOT(·), as well as low frontier energy levels and a small SOMO-LUMO gap, similar to 1(·), in spite of the loss of the degenerate LUMOs in symmetry-lowered 2(·), which is associated with the attachment of the weaker electron-accepting oxo group instead of the dicyanomethylene group in 1(·). These prominent results are attributable to the structural and electronic properties in the triangulene-based highly delocalized fused polycyclic neutral π-radical system.