Synthesis and interconversions of reduced, alkali–metal supported iron–sulfur–carbonyl complexes

Abstract

We report the synthesis, interconversions and X-ray structures of a set of [mFe-nS]-type carbonyl clusters (where S = S, S or RS; m = 2-3; n = 1-2). All of the clusters have been identified and characterized by single crystal X-ray diffraction, IR and C NMR. Reduction of the parent neutral dimer [μ-(SPh)Fe(CO)] (1) with KC affords an easily separable ∼1 : 1 mixture of the anionic, dimeric thiolate dimer K[Fe(SPh)(CO)(μ-CO)] (2) and the dianionic, sulfido trimer [K(benzo-15-crown-5)][Fe(μ-S)(CO)] (3). Oxidation of 2 with diphenyl-disulfide (PhS) cleanly returns the starting material 1. The Ph-S bond in 1 can be cleaved to form sulfide trimer 3. Oxidation of sulfido trimer 3 with [Fc](PF) in the presence of S cleanly affords the all-inorganic persulfide dimer [μ-(S)Fe(CO)] (4), a thermodynamically stable product. The inverse reactions to form 3 (dianion) from 4 (neutral) were not successful, and other products were obtained. For example, reduction of 4 with KC afforded the mixed valence Fe(i)/Fe(ii) species [((FeS)(CO))Fe] (5), in which the two {FeS(CO)} units serve as bidendate ligands to a Fe(ii) center. Another isolated product (THF insoluble portion) was recrystallized in MeCN to afford [K(benzo-15-crown-5)][((FeS)(CO))(μ-S)] (6), in which a persulfide dianion bridges two {2Fe-S} moieties (dimer of dimers). Finally, to close the interconversion loop, we converted the persulfide dimer 4 into the thiolate dimer 1 by reduction with KC followed by reaction with the diphenyl iodonium salt [PhI](PF), in modest yield. These reactions underscore the thermodynamic stability of the dimers 1 and 4, as well as the synthetic and crystallization versatility of using the crown/K counterion system for obtaining structural information on highly reduced iron-sulfur-carbonyl clusters.

Single‐Step Sulfur Insertions into Iron Carbide Carbonyl Clusters: Unlocking the Synthetic Door to FeMoco Analogues

“…In a similar vein, the Holm group reported an iron‐sulfur cluster that incorporates a silyl‐nitride into the cluster core [19] . Two reports from our group demonstrated a series of interconversions between Fe 2 S 2 and Fe 3 S clusters in preliminary work for modeling carbon‐atom insertion as seen in FeMoco biogenesis (Figure 1), [20, 21] although ultimately carbide insertion proved unsuccessful.…”

Combining metal–metal cooperativity, metal–ligand cooperativity and chemical non-innocence in diiron carbonyl complexes

“…We reason that this is due to the coordination of the potassium cation to carbonyl ligands, which is observed in the solidstate structure of 5 (Figure 3 and Figure S89) and has been reported to result in shorter C-O bonds 22a and lower the C-O stretching frequency. 26 The 31 P{ 1 H} NMR spectrum of 5 in THF-d 8 at 298 K displays two doublets at δ = 96.6 ppm (J = 5.2 Hz) and 86.6 ppm (J = 5.2 Hz), indicating that the phosphorous nuclei are magnetically coupled. As in 3, downfield shifted naphthyridine resonances and two methine/methylene doublets are observed at δ = 4.26 ppm ( 2 J H,P = 2.8 Hz) and 3.18 ppm ( 2 J H,P = 8.6 Hz), which are characteristic for a partially dearomatized iPr PNNP* ligand.…”

Combining Metal-Metal Cooperativity, Metal-Ligand Cooperativity and Chemical Non-Innocence in Diiron Carbonyl Complexes

“…We reason that this is due the coordination of the potassium cation to carbonyl ligands, which is observed in the solid-state structure of 5 (Figure 3 and Figure S89) and has been reported to result in shorter C-O bonds 22a and lower the C-O stretching frequency. 26 The 31 P{ 1 H} NMR spectrum of 5 in THF-d8 at 298 K displays two doublets at δ = 96.6 ppm (J = 5.2 Hz) and 86.6 ppm (J =5.2 Hz), indicating that the phosphorous nuclei are magnetically The observation of a single methylene resonance that integrates for two protons is indicative of a on average Cssymmetric species in solution. 27 Although the solid-state structure of 5 displays a bridging carbonyl ligand orthogonal to the naphthyridine plane (Figure 3), we reason that the µcarbonyl undergoes rapid exchange on the NMR timescale giving on average a Cs-symmetric species in solution.…”