Double-σ-Bonded Close-Shell Dimers and Peroxy-Linked Open-Shell Dimer Derived from a C3 Symmetric Trioxophenalenyl Neutral Diradical

A novel neutral diradical of pi-extended phenalenyl derivative having three oxo-groups, tri-tert-butyl-1,4,7-trioxophenalenyl, and two types of the corresponding sigma-dimers were investigated. Quantum chemical calculations showed that the neutral diradical is in triplet ground state having doubly degenerate singly occupied molecular orbitals. The neutral diradical undergoes a sigma-dimerization, generating two types of sigma-dimers immediately after the preparation. One of the sigma-dimers, which was selectively generated in the crystalline state, was a close-shell dimer linked through double-sigma-bonds on the phenalenyl skeleton with a long C-C bond length of 1.66 angstrom. The other sigma-dimer, which existed only in the solution state, was a peroxy-linked open-shell dimer in which one sigma-bond was formed between two oxygen atoms. Furthermore, the temperature-dependent H-1 NMR and ESR spectra revealed that these sigma-dimers are in equilibrium in the solution state by the reversible sigma-bond formation/cleavage via the neutral diradical as a key intermediate.

Automated summary

A novel neutral diradical and its corresponding dimers were investigated. The diradical was found to be in a triplet ground state with doubly degenerate singly occupied molecular orbitals. Upon preparation, the diradical underwent sigma-dimer formation, resulting in two types of dimers. One dimer existed only in the crystalline state, while the other dimer was observed only in solution. Temperature-dependent spectroscopic measurements revealed that these dimers were in equilibrium in solution, with the reversible formation/cleavage of sigma-bonds mediated by the neutral diradical.