Molybdenum–Iron–Sulfur Cluster with a Bridging Carbide Ligand as a Partial FeMoco Model: CO Activation, EPR Studies, and Bonding Insight
Linh Le, Tianyi He, Justin P. Joyce, Paul H. Oyala, Serena DeBeer, Theodor Agapie
Abstract
High Resolution Image Download MS PowerPoint Slide Nitrogenase enzymes catalyze the reduction of N 2 to NH 3 at a complex Fe-M (M = Mo, Fe, or V) cofactor (FeMco), which displays eight metal centers and sulfide and carbide bridges with a MFe 7 S 8 C composition. The role of the unusual μ 6 -carbide ligand and its effects on the metal centers remain unclear. Here, we describe the transfer of a carbide ligand to a MoFe 3 S 3 cluster supported by a bisphenoxide ligand from a previously reported terminal Mo carbide complex to yield a pentametallic cluster of MoS 3 Fe 3 CMo composition, which also displays a bridging CO that resembles the lo-CO form of nitrogenase. This cluster has an S = 1/2 spin state amenable to studies by pulse EPR spectroscopy, revealing a significantly larger carbide 13 C hyperfine interaction ( a iso ( 13 C) = 12.5 MHz) than any observed for various states of FeMoco studied by EPR thus far (| a iso ( 13 C)| = 0.89 to 2.7 MHz). This report provides a strategy for the synthesis of carbide-containing iron–sulfur clusters relevant to nitrogenase cluster modeling, as well as benchmarking information for the metal–carbon interactions by EPR methods.