Unusual Nitrite Complexes of Iron(III) and Iron(II) Stabilized by the Tris(3,5-dimethylpyrazolyl)borate Ligand

Halide metathesis with silver nitrite allows for either stepwise or complete substitution of all three chloride ligands in the iron(III) compound [NEt 4 ][HB(3,5-Me 2 pz) 3 FeCl 3 ] ( 1 ) to give the complexes [NEt 4 ][HB(3,5-Me 2 pz) 3 Fe(ONO) x Cl 3 - x ], x = 1−3 ( 2 − 4 ), and [NEt 4 ][HB(3,5-Me 2 pz) 3 Fe(η 2 -ONO)Cl] ( 5 ), which were characterized by elemental analyses, electrochemistry, and IR, EPR, and UV−vis spectroscopy. Single-crystal X-ray diffraction was used to characterize the ferric complexes 2 and 4 and the ferrous chelating nitrito complex 5 . The crystal structures of the ferric complexes exhibit monodentate, O−bound nitrito ligands, while the change in metal oxidation state from +3 to +2 leads to a chelating nitrito ligand in 5 .