Heterobimetallic Silver-Iron Complexes Involving Fe(CO)₅ Ligands

Iron(0) pentacarbonyl is an organometallic compound with a long history. It undergoes carbonyl displacement chemistry with various donors (L), leading to molecules of the type Fe(CO)_x(L)_5-x. The work reported here illustrates that Fe(CO)₅ can also act as a ligand. The reaction between Fe(CO)₅ with the silver salts AgSbF₆ and Ag[B{3,5-(CF₃)₂C₆H₃}₄] under appropriate conditions resulted in the formation of [(μ-H₂O)AgFe(CO)₅]₂[SbF₆]₂ and [B{3,5-(CF₃)₂C₆H₃}₄]AgFe(CO)₅, respectively, featuring heterobimetallic {Ag-Fe(CO)₅}⁺ fragments. The treatment of [B{3,5-(CF₃)₂C₆H₃}₄]AgFe(CO)₅ with 4,4'-dimethyl-2,2'-bipyridine (Me₂Bipy) and Fe(CO)₅ afforded a heterobimetallic [(Me₂Bipy)AgFe(CO)₅][B{3,5-(CF₃)₂C₆H₃}₄] species with a Ag-Fe(CO)₅ bond and a heterotrimetallic [{Fe(CO)₅}₂(μ-Ag)][B{3,5-(CF₃)₂C₆H₃}₄] with a (CO)₅Fe-Ag-Fe(CO)₅ core, respectively, illustrating that it is possible to manipulate the coordination sphere at silver while keeping the Ag-Fe bond intact. The chemistry of [B{3,5-(CF₃)₂C₆H₃}₄]AgFe(CO)₅ with Et₂O and PMes₃ (Mes = 2,4,6-trimethylphenyl) has also been investigated, which led to [(Et₂O)₃Ag][B{3,5-(CF₃)₂C₆H₃}₄] and [(Mes₃P)₂Ag][B{3,5-(CF₃)₂C₆H₃}₄] with the displacement of the Fe(CO)₅ ligand. X-ray structural and spectroscopic data of new molecules as well as results of computational analyses are presented. The Fe-Ag bond distances of these metal-only Lewis pairs range from 2.5833(4) to 2.6219(5) Å. These Ag-Fe bonds are of primarily an ionic/electrostatic nature with a modest amount of charge transfer between Ag⁺ and Fe(CO)₅. The ν̅(CO) bands of the molecules with Ag-Fe(CO)₅ bonds show a notable blue shift relative to those observed for free Fe(CO)₅, indicating a significant reduction in Fe→CO back-bonding upon its coordination to silver(I).