Multi-Site Reactivity: Reduction of Six Equivalents of Nitrite To Give an Fe6(NO)6 Cluster with a Dramatically Expanded Octahedral Core

Reaction of NO2– with the octahedral cluster (HL)2Fe6 in the presence of a proton source affords the hexanitrosyl cluster (HL)2Fe6(NO)6. This species forms via a proton-induced reduction of six nitrite molecules per cluster, utilizing each site available on the polynuclear core. Formation of the hexanitrosyl cluster is accompanied by a near 2-fold expansion of the (HL)2Fe6 core volume, where intracore Fe–Fe interactions are overcome by strong π-bonding between Fe centers and NO ligands. A core volume of this magnitude is rare in octahedral metal clusters not supported by interstitial atoms. Moreover, the structural flexibility afforded by the (HL)2Fe6 platform highlights the potential for other reaction chemistry involving species with metal–ligand multiple bonds. Carrying out the reaction of the cluster [(HL)2Fe6(NCMe)6]4+ with nitrite in the absence of a proton source serves to forestall the nitrite reduction and enables clean isolation of the intermediate hexanitro cluster [(HL)2Fe6(NO2)6]2–.