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

Neutral N-pyrazolyl radicals [3,5-R₂pz]^• as reactive intermediates were generated by one-electron oxidization of the corresponding 3,5-disubstituted pyrazolato anions [3,5-R₂pz]⁻ (R = tBu, Ph) with BiCl₃ and trapped by the use of 5,5-dimethyl-1-pyrroline-N-oxide as a spin trap, which was confirmed by electron paramagnetic resonance spectral analysis. With dimerization of the postulated pyrazolato low-valent Bi^II radical species, two novel paddlewheel pyrazolatodibismuthanes [L₂(Bi–Bi)­L₂] [L = η¹,η¹-3,5-R₂pz; R = tBu (5α, 5β, and 5γ), Ph (6)] were isolated and structurally characterized.