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

Abstract

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.