Thermal Growth of Au-Fe Heterometallic Carbonyl Clusters Containing N-Heterocyclic Carbene and Phosphine Ligands.

The thermal reactions of [NEt][Fe(CO)(AuNHC)] [NHC = IMes ([NEt][]) or IPr ([NEt][]); IMes = CNH(CHMe); IPr = CNH(CHPr)], Fe(CO)(AuNHC) [NHC = IMes () or IPr ()], Fe(CO)(AuIMes)(AuIPr) (), and Fe(CO)(AuNHC)(AuPPh) [NHC = IMes () or IPr ()] were investigated in different solvents [CHCl, CHCN, dimethylformamide, and dimethyl sulfoxide (dmso)] and at different temperatures (50-160 °C) in an attempt to obtain higher-nuclearity clusters. and completely decomposed in refluxing CHCl, resulting in [Fe(CO)(AuNHC)] [NHC = IMes () or IPr ()]. Traces of [Fe(CO)(CCH)] () were obtained as a side product. Conversely, decomposed in refluxing CHCN, affording the new cluster [Au{Fe(CO)}(PPh)] (). The relative stability of the two isomers found in the solid state structure of was computationally investigated. was very stable, and only after prolonged heating above 150 °C in dmso was limited decomposition observed, affording small amounts of [FeS(CO)] (), [HFe(CO)] (), and [AuS{Fe(CO)}(IPr)] (). A dicationic nature for was proposed on the basis of density functional theory calculations. All of the other reactions examined led to species that were previously reported. The molecular structures of the new clusters , , , and were determined by single-crystal X-ray diffraction as their [NEt][]·1.5toluene, [Au(IMes)][]·0.67CHCl, [NEt][], and [][BF]·solvent salts, respectively.