Nitrogen-fixing organisms perform dinitrogen reduction to ammonia at an Fe-M (M = Mo, Fe, or V) cofactor (FeMco) of nitrogenase. FeMco displays eight metal centers bridged by sulfides and a carbide having the MFe₇S₈C cluster composition. The role of the carbide ligand, a unique motif in protein active sites, remains poorly understood. Toward addressing how the carbon bridge affects the physical and chemical properties of the cluster, we isolated synthetic models of subsite MFe₃S₃C displaying sulfides and a chelating carbyne ligand. We developed synthetic protocols for structurally related clusters, [Tp*M’Fe₃S₃X]ⁿ⁻, where M’ = Mo or W, the bridging ligand X = CR, N, NR, S, and Tp* = Tris(3,5-dimethyl-1-pyrazolyl)hydroborate, to study the effects of the identity of the heterometal and the bridging X group on structure and electrochemistry. While the nature of M’ results in minor changes, the chelating, μ₃-bridging carbyne has a large impact on reduction potentials, being up to 1 V more reducing compared to nonchelating N and S analogs.

固氮生物在固氮酶的 Fe-M（M = Mo、Fe 或 V）辅因子 (FeMco) 处将二氮还原为氨。FeMco 显示由硫化物和具有 MFe ₇ S ₈ C 簇组成的碳化物桥接的八个金属中心。碳化物配体（蛋白质活性位点中的独特基序）的作用仍然知之甚少。为了解决碳桥如何影响簇的物理和化学性质，我们分离了显示硫化物和螯合碳炔配体的子位点 MFe ₃ S _{3 C 的合成模型。}我们为结构相关的簇开发了合成协议，[Tp*M'Fe ₃ S ₃ X] ⁿ⁻，其中 M' = Mo 或 W，桥接配体 X = CR、N、NR、S 和 Tp* = Tris(3,5-dimethyl-1-pyrazolyl)hydroborate，以研究异金属特性的影响以及结构和电化学上的桥接 X 基团。虽然 M' 的性质导致微小的变化，但螯合的 μ ₃ -桥联碳炔对还原电位有很大影响，与非螯合 N 和 S 类似物相比，还原电位最多可降低 1 V。