Nitride-Bridged Mo−Fe−S Double-Cubanes: Syntheses, Redox Behaviors and Comparison with their W Analogs

The FeMo cofactor (FeMoco) of the Mo-dependent nitrogenase was identified as a Mo−Fe−S cluster incorporating a 2p atom in the core. The edge-bridged double-cubane (EBDC, [M₂Fe₆(μ₃-S)₆(μ₄-S)₂]^z (M=Mo/V; z denotes charge)) clusters were demonstrated to undergo rearrangement reactions to generate the apex-fused double-cubane clusters ([M₂Fe₆(μ₂-S)₂(μ₃-S)₆(μ₆-S)]^z) as mimics of the P^N-clusters. The introduction of 2p atoms into the core of EBDC clusters will furnish the possibility of mimicking the FeMoco structure through rearrangement. In this work, an EBDC Mo−Fe−S cluster with core nitrides, namely [(Tp*)₂Mo₂Fe₆(μ₄-N)₂S₆Cl₄]²⁻ (Tp*=tris(3,5-dimethyl-1-pyrazolyl)hydroborate), has been synthesized. Subsequent terminal ligand substitution has produced a series of EBDC clusters with isostructural cores. Further studies of the series of nitride-containing EBDC clusters are focused on their structures and redox properties, as well as comparisons with their W analogs. The results indicate that the core structures of these clusters are affected by distinct hetero-metal centers and different terminal ligands to a limited extent, but the redox behavior and redox potentials of these clusters differ significantly. This work provides us with a viable method for regulating the properties of the nitride-containing EBDC clusters, which may be enlightening for further studies of the rearrangement reactions towards mimicking the FeMoco structure.