Direct Evidence for Neutral <i>N</i>‑Pyrazolyl Radicals: Paddlewheel Dibismuthanes Bearing Pyrazolato Ligands with Very Short Bi–Bi Single Bonds

Neutral <i>N</i>-pyrazolyl radicals [3,5-R<sub>2</sub>pz]<sup>•</sup> as reactive intermediates were generated by one-electron oxidization of the corresponding 3,5-disubstituted pyrazolato anions [3,5-R<sub>2</sub>pz]<sup>−</sup> (R = <i>t</i>Bu, Ph) with BiCl<sub>3</sub> and trapped by the use of 5,5-dimethyl-1-pyrroline-<i>N</i>-oxide as a spin trap, which was confirmed by electron paramagnetic resonance spectral analysis. With dimerization of the postulated pyrazolato low-valent Bi<sup>II</sup> radical species, two novel paddlewheel pyrazolatodibismuthanes [L<sub>2</sub>(Bi–Bi)­L<sub>2</sub>] [L = η<sup>1</sup>,η<sup>1</sup>-3,5-R<sub>2</sub>pz; R = <i>t</i>Bu (<b>5α</b>, <b>5β</b>, and <b>5γ</b>), Ph (<b>6</b>)] were isolated and structurally characterized.