Thermal Growth of Au–Fe Heterometallic Carbonyl Clusters Containing N‑Heterocyclic Carbene and Phosphine Ligands

The thermal reactions
of [NEt4]­[Fe­(CO)4(AuNHC)]
[NHC = IMes ([NEt4]­[1]) or IPr ([NEt4]­[2]); IMes = C3N2H2(C6H2Me3)2; IPr = C3N2H2(C6H3iPr2)2], Fe­(CO)4(AuNHC)2 [NHC = IMes (3) or IPr (4)], Fe­(CO)4(AuIMes)­(AuIPr) (5), and Fe­(CO)4(AuNHC)­(AuPPh3) [NHC = IMes (6) or IPr (7)] were
investigated in different solvents [CH2Cl2,
CH3CN, dimethylformamide, and dimethyl sulfoxide (dmso)]
and at different temperatures (50–160 °C) in an attempt
to obtain higher-nuclearity clusters. 1 and 2 completely decomposed in refluxing CH2Cl2,
resulting in [Fe2(CO)8(AuNHC)]− [NHC = IMes (10) or IPr (11)]. Traces
of [Fe3(CO)10(CCH3)]− (12) were obtained as a side product. Conversely, 6 decomposed in refluxing CH3CN, affording the
new cluster [Au3{Fe­(CO)4}2(PPh3)2]− (15). The relative
stability of the two isomers found in the solid state structure of 15 was computationally investigated. 4 was very
stable, and only after prolonged heating above 150 °C in dmso
was limited decomposition observed, affording small amounts of [Fe3S­(CO)9]2– (9), [HFe­(CO)4]− (16), and [Au16S­{Fe­(CO)4}4(IPr)4]n+ (17). A dicationic nature for 17 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 11, 12, 15, and 17 were determined
by single-crystal X-ray diffraction as their [NEt4]­[11]·1.5toluene, [Au­(IMes)2]­[15]·0.67CH2Cl2, [NEt4]­[12], and [17]­[BF4]n·solvent salts, respectively.