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

Abstract

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 ν(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).