A Bidentate Carbene Ligand Stabilizes a Low-Coordinate Iron(0) Carbonyl Complex

The bulky bis­(carbene)­borate ligand Ph2B­(tBuIm)2– stabilizes low-coordinate and low-valent iron complexes. The four-coordinate iron­(II) complex Ph2B­(tBuIm)2FeCl­(THF) is a precursor to the low-spin iron­(I) complex Ph2B­(tBuIm)2Fe­(CO)3. Despite a reversible reduction wave in the cyclic voltammogram, access to the iron(0) complex [Ph2B­(tBuIm)2Fe­(CO)3]− requires reduction under a CO atmosphere. Without excess CO, KC8 reduction leads to formation of the dimer K2[Ph2B­(tBuIm)2Fe­(CO)2] along with loss of CO. Each iron center in this complex adopts a distorted-square-planar geometry. Spectroscopic analysis of these carbonyl complexes reveals the very high strength of the bis­(carbene)­borate ligand.