Controlled Expansion of a Strong-Field Iron-Nitride Cluster: Multi-Site Ligand Substitution as a Strategy for Activating Interstitial Nitride Nucleophilicity.

Multimetallic clusters have long been investigated as molecular surrogates for reactive sites on metal surfaces. In the case of the mu(4)-nitrido cluster [Fe-4(mu(4)-N)(CO)(12)](-), this analogy is limited owing to the electron-withdrawing effect of carbonyl ligands on the iron nitride core. Described here is the synthesis and reactivity of [Fe-4(mu(4)-N)(CO)(8)(CNArMes2)(4)](-), an electron-rich analogue of [Fe-4(mu(4)-N)(CO)(12)](-), where the interstitial nitride displays significant nucleophilicity. This characteristic enables rational expansion with main-group and transition-metal centers to yield unsaturated sites. The resulting clusters display surface-like reactivity through coordination-sphere-dependent atom rearrangement and metal-metal cooperativity.