Sulfur-Ligated [2Fe-2C] Clusters as Synthetic Model Systems for Nitrogenase

Abstract

Metal clusters featuring carbon and sulfur donors have coordination environments comparable to the active site of nitrogenase enzymes. Here, we report a series of di-iron clusters supported by the dianionic yldiide ligands, in which the Fe sites are bridged by two μ 2 -C atoms and four pendant S donors.The [L 2 Fe 2 ] (L = {[Ph 2 P(S)] 2 C} 2− ) cluster is isolable in two oxidation levels, all-ferrous Fe 2 II and mixed-valence Fe II Fe III . The mixed-valence cluster displays two peaks in the Mossbauer spectra, indicating slow electron transfer between the two sites. The addition of the Lewis base 4-dimethylaminopyridine to the Fe 2 II cluster results in coordination with only one of the two Fe sites, even in the presence of an excess base. Conversely, the cluster reacts with 8 equiv of isocyanide t BuNC to give a monometallic complex featuring a new C−C bond between the ligand backbone and the isocyanide. The electronic structure descriptions of these complexes are further supported by X-ray absorption and resonant X-ray emission spectroscopies.

One Ligand to Bind them All: S~C~S2− Carbon‐ and Sulfur‐Based Gem‐Dianion as Structuring Ligand for Iron Polymetallic Assemblies

“…Spectroscopic characterizations along with crystallographic data matched exactly with our previous report. In particular, the zero-field Mössbauer spectrum of complex 1 displays a single quadrupole doublet with parameters (δ = 0.66 mm/s, ΔE Q = 3.47 mm/s) that are consistent with those reported by Holland for the same complex [12] (see Supporting Information Figure S36) confirming the assignment as two equivalent high-spin Fe(II) centers. Cyclic Voltammetry of complex 1 in dichloromethane showed a reversible oxidation at 0.24 V vs SCE, and an irreversible reduction wave at À 1.23 V vs SCE.…”

“…We reported in 2012 [11] an iron dimer, complex 1 , that presents interesting similarities with the FeMo‐co structure, also highlighted by Holland, de Beer and co‐workers during the course of the present work [12] . The unique structure of this complex lies on the peculiar properties of the bis(thiophosphinoylmethane)diide ligand (SCS) 2− which have proven to be extremely versatile.…”

“…[5] We reported in 2012 [11] an iron dimer, complex 1, that presents interesting similarities with the FeMo-co structure, also highlighted by Holland, de Beer and co-workers during the course of the present work. [12] The unique structure of this complex lies on the peculiar properties of the bis(thiophosphinoylmethane)diide ligand (SCS) 2À which have proven to be extremely versatile. Featuring an excellent balance between strong charge and efficient stabilization by thiophosphinoyl substituents, this ligand is able to stabilize a variety of complexes of rare earth, [13] actinide [14] and early [15] to late [16] transition metals.…”

Introducing SpectraFit: An Open-Source Tool for Interactive Spectral Analysis

“…Our findings indicate that the optimal models for fitting comprise of two peaks that are linked to the pre-edge, followed by three peaks that are associated with charge transfer and the rising edge regime . Our approach also uses cumulative Gaussian functions to represent the edge jump, which is associated with the ionization potential .…”

“…16,28 ■ RESULTS AND DISCUSSION Features and Usage. To demonstrate SpectraFit's features and workflow, previously published X-ray spectra 7 on iron− sulfur model complexes for nitrogenase are analyzed in this section; see also the "Notice to the Reader" at the end of the publication. Figure 2 displays the two complexes for this demonstration, two di-iron clusters [L 2 Fe 2 ] and [L 2 Fe 2 ]-{DMAP}, labeled as 1 and 2.…”