Modulation of Open-Shell Character in Dibenzoazaborine Dications through Amino-Substituent Modification

Oxidation of dibutylamino-substituted dibenzoazaborine Bu2NDBAB afforded the air-stable dication [Bu2NDBAB](SbF6)2 in 83% yield, with an NIR absorption band at 943 nm. Structural analysis revealed pronounced oxidation-induced quinoidal distortion. Unlike the previously reported diarylamino-substituted analogue [Ar2NDBAB]2+, the present dication exhibited well-resolved 1H NMR signals, and no ESR signal attributable to the dication was detected. Although the broken-symmetry open-shell (BS-OS) solution was the lowest-energy solution, its small diradical character (y = 0.122, compared with 0.324 for [Ar2NDBAB]2+) indicates only a limited open-shell contribution. Spin-density and natural spin-population analyses showed that replacement of the Ar2N groups with Bu2N groups suppresses peripheral spin delocalization, resulting in a singlet ground state with predominantly closed-shell character. Nucleus-independent chemical shift (NICS) calculations further indicated antiaromatic character of the azaborine ring in the present dication. These results demonstrate amino-substituent control of open-shell character in DBAB dications.