Heterobimetallic Complexes Featuring Fe(CO)₅ as a Ligand on Gold

Iron(0) pentacarbonyl complexes of gold(I), [Mes₃PAu-Fe(CO)₅][SbF₆] (1) and [(IPr*)Au-Fe(CO)₅][SbF₆] (2) (Mes=2,4,6-trimethylphenyl; IPr*=1,3-bis(2,6-bis(diphenylmethyl)-4-methylphenyl)imidazol-2-ylidene) have been synthesized using Mes₃PAuCl and (IPr*)AuCl as the gold(I) precursor, AgSbF₆ halide ion abstractor, and the Lewis base Fe(CO)₅. The Au−Fe bond lengths of these metal-only Lewis pair complexes are significantly shorter than the sum of the experimentally derived covalent radii of Au and Fe. The v̄(CO) bands of the molecules show a notable blueshift relative to those observed for free Fe(CO)₅, indicating a substantial reduction in Fe→CO backbonding upon its coordination to gold(I) with either Mes₃P or IPr* supporting ligands (L). The analysis of the electronic structure with quantum chemical method suggests that the Au−Fe bond consists mainly of [LAu]⁺←Fe(CO)₅ σ-donation and weaker [LAu]⁺→Fe(CO)₅ π-backdonation. The donor strength of Fe(CO)₅ is similar to that of CO.