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 BiII 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.