Low-Coordinate Iron(II) Complexes of a Bulky Bis(carbene)borate Ligand

The bulky bis­(carbene)­borate ligand H2B­(tBuIm)2– allows for the synthesis of three- and four-coordinate iron­(II) complexes, including heteroleptic H2B­(tBuIm)2FeN­(TMS)2 and homoleptic [H2B­(tBuIm)2]2Fe. The magnetic properties of these coordinatively unsaturated complexes have been characterized by SQUID magnetometry, but no evidence of single-molecule magnet behavior is observed, despite large negative uniaxial zero field splitting. The three-coordinate complex H2B­(tBuIm)2FeN­(TMS)2 serves as a precursor for the synthesis of the four-coordinate mixed carbene complex H2B­(tBuIm)2(iPr2Im)­FeCl, which has a coordination environment similar to that found in tris­(carbene)­borate iron­(II) chloride complexes. Despite this similarity, attempts to prepare the corresponding iron­(IV) nitride were unsuccessful, suggesting that subtle structural factors are critical to stabilizing this species.