Heterobimetallic Complexes with Polar, Unsupported Cu–Fe and Zn–Fe Bonds Stabilized by N‑Heterocyclic Carbenes

Abstract

Heterobimetallic complexes of the formulations (NHC)­Cu–FeCp­(CO)₂ (NHC = IPr, IMes, SIMes), (IPr)­Cu–MoCp­(CO)₃, and (IPr)­(Cl)­Zn–FeCp­(CO)₂ were synthesized in high yield from readily available starting materials and characterized crystallographically. The solid-state structures of the Cu–Fe systems reveal close, secondary interactions between Cu and one CO ligand from the [FeCp­(CO)₂] unit that are absent in the Zn–Fe analogue. The heterobimetallic complexes feature short yet polar Cu–Fe, Cu–Mo, and Zn–Fe bonds in which the electrophilic metal (Cu, Zn) is later in the transition series than the nucleophilic metal (Fe, Mo), thereby subverting the more common early–late heterobimetallic paradigm. DFT analyses were used to assess M–M′ bond polarity and examine effects on M–M′ bonding of systematic modifications to both the nucleophilic and electrophilic fragments. Experimental confirmation of Cu–Fe bond polarity was obtained by analysis of product mixtures resulting from the reactions between (NHC)­Cu–FeCp­(CO)₂ complexes and MeI, which produced (NHC)­Cu–I and Me–FeCp­(CO)₂ products