Synthesis of the Highly Reduced [Fe6C(CO)15]4– Carbonyl Carbide Cluster and Its Reactions with H+ and [Au(PPh3)]+

The reduction of [Fe6C(CO)16]2– (1) with NaOH in DMSO or with Na/naphthalene in THF affords the highly reduced [Fe6C(CO)15]4– (2) monocarbide tetraanion. The molecular structure of 2 has been crystallographically determined as its [Et4N]4[Fe6C(CO)15]·CH3CN salt, revealing an octahedral structure as expected for a hexanuclear cluster possessing 86 valence electrons. The stepwise protonation of 2 with strong acids such as HBF4·Et2O results first in the monohydride trianion [HFe6C(CO)15]3– (3) and then the purported dihydride dianion [H2Fe6C(CO)15]2– (4), as indicated by 1H NMR spectroscopy. Both 3 and 4 are not stable enough to be isolated and rapidly decompose, yielding the parent dianion 1. The reaction of 2 with a slight excess of Au(PPh3)Cl affords the aurated dianion [Fe6C(CO)15(AuPPh3)2]2– (5), which has been isolated and structurally characterized as its [Et4N]2[Fe6C(CO)15(AuPPh3)2]·2CH3CN salt. DFT calculations allowed us to study, from a computational point of view, the electronic features of the new compounds and possible reaction intermediates.