Isolable Bis-BN-Based Analogues of Müller's Hydrocarbon

Müller's hydrocarbon and its analogues are classical examples of Kekulé diradicaloids and have gained great attention.However,because of their high reactivities,their isolation and structural characterizations are still challenging.Herein,we report the isolation of two bis-BN-based analogues of Müller's hydrocarbon (1 and 2) as crystalline solids in moderate yields.Experimental results and theoretical studies demonstrated that compound 1 possessing the terminal 1,3,2-diazaboryl groups is an open-shell singlet diradicaloid,which is in contrast to the closed-shell singlet ground states of the bis-BN-based analogues of Thiele's and Chichibabin's hydrocarbons with the same terminal groups,illustrating the strong influence of the central linkers on the ground state.Additionally,the replacement of the terminal 1,3,2-diazaboryl groups in 1 with the bis(2,4,6-triisopropylphenyl)boryl groups affords 2 with higher diradical character and a smaller singlet-triplet energy gap.

Crystalline Germanium-Dipyrromethene Radicals:from a Delocalized Neutral to a Localized Cation

Both dipyrromethene complexes and radicals of heavier main group elements have been of high interest.However,cationic germanium radicals and dipyrromethene-based radicals of heavier main group elements are still escaped to be isolated.Herein,we report the isolation and full characterization of a neutral Ge(I)-masked dipyrromethene-based radical 3 and the first cationic Ge(III)-centered radical 5^(·+)as stable crystalline solids.3 behaves as a germanium(I)radical in its reaction with diphenyl disulfide to form the Ge-S bond,although X-ray crystallographic,EPR spectroscopic,computational studies revealed that the unpaired electron of 3 is mainly delocalized over the C_(9)N_(2)Ge backbone and the allylic radical character is also significant in 3.In contrast to 3,the spin density of 5^(·+)is mainly localized at the Ge center with minor contribution from the dipyrromethene ligand.Moreover,reduction of 5^(·+)with potassium graphite quantitatively regenerates 5,illustrating a reversible one-electron redox pair.

Room-Temperature Reversibleσ-Dimerization of a Phenalenyl Radical

Phenalenyl derivatives have been of tremendous interest due to their reversible dimerization in response to the external stimuli such as temperature.However,most of PLY derivatives only show the reversibility dependent on temperature.Herein,we report a unique PLY-based radical anionic salt with reversibleσ-dimerization controlled by solvent rather than temperature.The structure and reversibility of this PLY anion system have been spectroscopically,crystallographically,and theoretically investigated.The molecule exists mainly as theσ-dimer form of K2[σ-12]in toluene,while it can be broken into the monomeric radical anion 1•–by re-dissolving in THF.Moreover,when THF is replaced with toluene,radical 1•–could beσ-dimerized back again.Theoretical calculations reveal that the potassium ions are necessary for the formation of theσ-dimer and the solvent polarity controls theσ-dimerization by regulating the presence of K+.