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 μ ₄ -nitrido cluster [Fe ₄ (μ 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 (μ ₄ -N)(CO) ₈ (CNAr ^Mes2 ) ₄ ] ^- , an electron-rich analogue of [Fe ₄ (μ 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.
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