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

Iron(0) pentacarbonyl complexes of gold(I), [Mes3 PAu-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 Mes3 PAuCl 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 Mes3 P 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.