From Ylides to Doubly Yldiide-Bridged Iron(II) High Spin Dimers via Self-Protolysis

Abstract

A synthetic strategy for the preparation of novel doubly yldiide bridged iron(II) high spin dimers ([(μ2-C)FeL]2, L = N(SiMe3)2, Mesityl) has been developed. This includes the synthesis of ylide-iron(II) monomers [(Ylide)FeL2] via adduct formation. Subsequent self-protolysis at elevated temperatures by in situ deprotonation of the ylide ligands results in a dimerization reaction forming the desired bridging μ2-C yldiide ligands in [(μ2-C)FeL]2. The comprehensive structural and electronic analysis of dimers [(μ2-C)FeL]2, including NMR, Mössbauer, and X-ray spectroscopy, as well as X-ray crystallography, SQUID, and DFT calculations, confirm their high-spin FeII configurations. Interestingly, the Fe2C2 cores display very acute Fe–C–Fe angles (averaged: 78.6(2)°) resulting in short Fe···Fe distances (averaged: 2.588(2) Å). A remarkably strong antiferromagnetic coupling between the Fe centers has been identified. Strongly polarized Fe–C bonds are observed where the negative charge is mostly centered at the μ2-C yldiide ligands.

The influences of carbon donor ligands on biomimetic multi-iron complexes for N2reduction

“…The overlap (J) was À84 cm À1 for [L Me FeS] 2 and À313 cm À1 for 2, but these values from a single reference DFT calculation relative to experiment are commonly overestimated. [63][64][65][66] Calculated spectra (Fig. S41-43 †) were thus obtained using the lowest energy solution with S ¼ 0.…”

Construction of Synthetic Models for Nitrogenase-Relevant NifB Biogenesis Intermediates and Iron-Carbide-Sulfide Clusters

“…Additionally, Yogendra et al recently reported a set of dimeric, yldiide-bridged iron complexes accessed from the known monomers. Magnetic susceptibility and spectroscopic studies of these dimers show intense antiferromagnetic coupling between iron sites and pronounced negative charge localization on the C ligand [53]. The Holland group reported a series of β-diketiminate complexes with various bridging C-donors.…”

Mixed-Valent Diiron μ-Carbyne, μ-Hydride Complexes: Implications for Nitrogenase

“…However, analogous studies for systems containing an Fe-(µ-C)-Fe linkage are not known, apart from a single report of pulse EPR data for 13 C-labelled S = 3/2 resting state of FeMoco. 1 Carbonbridged, multimetallic iron complexes are not uncommon, [57][58][59][60][61][62][63][64][65] but, with few exceptions, [66][67][68][69][70][71] these species have closed shell electronic configurations. Those that are paramagnetic all exhibit integer spin states and, thus, are not readily characterized by pulse EPR methods.…”

“…Those that are paramagnetic all exhibit integer spin states and, thus, are not readily characterized by pulse EPR methods. [66][67][68][69][70][71] To the best of our knowledge, only one synthetic iron complex featuring a carbon-based, Xn-type (n = 1,2,3) ligand with 13 C labelling, namely an iron(V)-carbyne complex with terminal 13 Ccarbyne, has been interrogated by pulse EPR. 44 Enzymatic iron-alkyl species have been isotopically labelled and investigated by ENDOR and/or HYSCORE spectroscopy, 72-74 but none have been structurally characterized and questions remain regarding their 2 electronic structure.…”

“…However, analogous studies for systems containing an Fe-(μ-C)-Fe linkage are not known, apart from a single report of pulse EPR data for the 13 C-labeled S = 3/2 resting state of FeMoco . Carbon-bridged, multimetallic iron complexes are not uncommon, − but with few exceptions, − these species have closed shell electronic configurations. Those that are paramagnetic all exhibit integer spin states and, thus, are not readily characterized by pulse EPR methods. − To the best of our knowledge, only one synthetic iron complex featuring a carbon-based, X n -type ( n = 1,2,3) ligand with 13 C labeling, namely an iron­(V)-carbyne complex with terminal 13 C-carbyne, has been interrogated by pulse EPR .…”