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-Rpz] as reactive intermediates were generated by one-electron oxidization of the corresponding 3,5-disubstituted pyrazolato anions [3,5-Rpz] (R = tBu, Ph) with BiCl 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 radical species, two novel paddlewheel pyrazolatodibismuthanes [L(Bi-Bi)L] [L = η,η-3,5-Rpz; R = tBu (5α, 5β, and 5γ), Ph (6)] were isolated and structurally characterized.