[2Fe–2S] Cluster Supported by Redox-Active o-Phenylenediamide Ligands and Its Application toward Dinitrogen Reduction

Abstract

As prevalent cofactors in living organisms, iron−sulfur clusters participate in not only the electron-transfer processes but also the biosynthesis of other cofactors. Many synthetic iron−sulfur clusters have been used in model studies, aiming to mimic their biological functions and to gain mechanistic insight into the related biological systems. The smallest [2Fe−2S] clusters are typically used for one-electron processes because of their limited capacity. Our group is interested in functionalizing small iron−sulfur clusters with redox-active ligands to enhance their electron storage capacity, because such functionalized clusters can potentially mediate multielectron chemical transformations. Herein we report the synthesis, structural characterization, and catalytic activity of a diferric [2Fe− 2S] cluster functionalized with two o-phenylenediamide ligands. The electrochemical and chemical reductions of such a cluster revealed rich redox chemistry. The functionalized diferric cluster can store up to four electrons reversibly, where the first two reduction events are ligand-based and the remainder metal-based. The diferric [2Fe−2S] cluster displays catalytic activity toward silylation of dinitrogen, affording up to 88 equiv of the amine product per iron center.

Synthesis and Structure of Thiolate‐Bridged Diiron and Dicobalt Complexes Supported by Modified β‐Diketiminate Ligands

“…The corresponding Mössbauer spectroscopic data can be satisfactorily fitted with a well‐resolved quadrupole doublet with δ of 0.59 mm/s and Δ E Q of 1.76 mm/s, which implies the two four‐coordinate Fe 2+ centers are both located in the same coordination environment. These parameters are obviously lower than those of the related {Fe 2 S 2 }‐type complexes featuring two high‐spin divalent iron ( S =2) centres supported by two imine donors, [17] which suggests the two iron centers are both in intermediate spin state S =1 with ferromagnetic coupling. This assumption is in good agreement with the solution magnetic moment of 4.95 μ B for 3 in a total spin state S tot =2.…”

Isostructural bridging diferrous chalcogenide cores [FeII(μ-E)FeII] (E = O, S, Se, Te) with decreasing antiferromagnetic coupling down the chalcogenide series

“…Likewise, bridging iron sulfide complexes are equally prevalent in nature, since iron-sulfur clusters found in the FeMoCo of the ATP-dependent nitrogenase enzymes are responsible and indispensable in delivering multiple equivalents of electrons during the catalytic cycle for the fixation of nitrogen. 45,46 Many compounds with Fe(μ-S) 2 Fe 47–55 cores and even higher nuclearities, 56–59 especially cubane-type structures, 60–63 have been well explored. Surprisingly, complexes having mono-bridged Fe(μ-S)Fe 28,57–82 cores are not as common as their O-counterparts, with crystallographically characterized synthetic examples numbering in the tens.…”

Rhodium diamidobenzene complexes: a tale of different substituents on the diamidobenzene ligand

“…[39][40][41][42][43] This fact is surprising considering the extreme variations that fundamentally different kinds of R substituents would allow in terms of tuning the steric, and in particular the electronic properties of the compounds. Various studies have proven the utility of o-diiminoquinonoid ligands in diverse areas such as photochemistry, 44,45 molecular magnetism, [46][47][48][49] electrocatalysis 50,51 and activation of small molecules [52][53][54][55] . A pertinent example is the aforementioned work by the group of Itoh, who used a Rh III halfsandwich complex with a singly-oxidized, open-shell ligand in the amination of trisylazide.…”

“…Various studies have proven the utility of o -diiminoquinonoid ligands in diverse areas such as photochemistry, 44,45 molecular magnetism, 46–49 electrocatalysis 50,51 and activation of small molecules. 52–55 A pertinent example is the aforementioned work by the group of Itoh, who used a Rh iii half-sandwich complex with a singly-oxidized, open-shell ligand in the amination of trisylazide. 9 We have recently shown the ligand-centered redox activity and the ensuing reactivity of diamidobenzene complexes of [Cp*Ir iii ].…”