Synthesis and characterization of heterometallic complexes involving coinage metals and isoelectronic Fe(CO)5, [Mn(CO)5]− and [Fe(CO)4CN]− ligands

Abstract

The chemistry of coinage metal ions with Fe(CO)₅, [Mn(CO)₅]⁻ and [Fe(CO)₄CN]⁻ has been explored using Mes₃P and N-heterocyclic carbene supporting ligands. A comparison of [(SIPr)Au–Fe(CO)₅][SbF₆], [(^Et2CAAC)Au–Fe(CO)₅][SbF₆] and [(Mes₃P)Au–Fe(CO)₅][SbF₆] shows that the ligand donor strength towards Au(I) follows the order Mes₃P > ^Et2CAAC > SIPr. These Fe(CO)₅ complexes show significant blue shifts in _CO bands relative to those observed for free Fe(CO)₅ as a result of it serving as a net electron donor to Au(I). Au(I) is a much stronger acceptor in (SIPr)Au–Mn(CO)₅ compared to Ag(I) in (SIPr)Ag–Mn(CO)₅. The structural details of Mes₃PAu–Mn(CO)₅ are also presented. [Fe(CO)₄CN]⁻ afforded CN bridged coinage metal complexes with (IPr*)Au⁺, (SIPr)Ag⁺ and (SIPr)Cu⁺ moieties, rather than molecules with direct Fe/coinage metal bonds. The computed total interaction energies indicate that both [Mn(CO)₅]⁻ and [Fe(CO)₄CN]⁻ are stronger donors toward Au(I) than Fe(CO)₅. A detailed analysis of the bonding interactions between the coinage metal ions and Fe(CO)₅, [Mn(CO)₅]⁻ and [Fe(CO)₄CN]⁻ suggests that the largest contribution comes from electrostatic attraction, while the covalent component follows the Dewar–Chatt–Duncanson model. The σ-donor interactions of these organometallic ligands with coinage metal ions are considerably stronger than the π-backbonding from the coinage metal ions.