The Mixed-Valence Double-Cubanoid Cluster [Fe8S12(ButNC)12]:  Synthesis, Structure, and Exchange Coupling of a New Structural Array of Four Fe(III) Sites

Goh, Christopher; Nivorozhkin, A. L.; Yoo, Sun Jae; Bominaar, Emile L.; Münck, Eckard; Holm, R. H.

doi:10.1021/ic980085t

Cited by 18 publications

(8 citation statements)

References 29 publications

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“…An XRD experiment confirmed the assignment of this product as [(IMes) 3 Fe 4 S 4 (CN t Bu)][BAr F 4 ] ( 5 ; Figure ). Consistent with the tetrahedral Fe geometry and high-spin state, the Fe–C bond is long (1.972(2) Å) in comparison to those of other Fe–S cluster isocyanide complexes (Fe–C(av) 1.84(3) Å), all of which adopt a local low-spin configuration. − Outside of its unprecedented nature in the Fe–S cluster literature, 5 is an uncommon example of a structurally characterized, terminal Fe isocyanide complex with a high-spin ground state. − …”

Section: Resultsmentioning

confidence: 82%

“…We next sought to determine if the IMes ligands in 4 exert sufficient steric pressure at the apical Fe site to prevent formation of a coordinatively saturated, octahedral geometry upon substitution of the ether ligand with one or more strong-field ligands. We elected to study isocyanide binding because isocyanides are isoelectronic with N 2 and CO (substrates for synthetic and biogenic Fe–S clusters) and because of the strong driving force for binding 3 equiv of isocyanide to generate a valence-localized, low-spin Fe 2+ site: all reported examples of isocyanide binding to [Fe 4 S 4 ] clusters demonstrate that binding three isocyanides is more favorable than binding one or two (e.g., Scheme A). − We therefore expected that, if sterically feasible, the apical Fe in 4 would also bind 3 equiv of isocyanide. On the other hand, if the IMes ligands impart sufficient steric pressure at the unique Fe site, only one isocyanide would bind, maintaining the apical Fe in a local high-spin configuration.…”

Section: Resultsmentioning

confidence: 99%

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Controlling Substrate Binding to Fe₄S₄ Clusters through Remote Steric Effects

Brown

Suess

2019

Inorg. Chem.

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The extraordinary reactivity exhibited by many Fe-S enzymes is due in large part to the influence of the protein scaffold on substrate binding and activation. In principle, the coordination chemistry of synthetic Fe-S clusters could similarly be controlled through remote steric effects. Toward this end, we report the synthesis of 3:1 site-differentiated [Fe4S4] clusters ligated by Nheterocyclic carbene (NHC) ligands with variable steric profiles: IMes (1,3-dimesitylimidazol-2ylidene) and I i Pr Me (1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene). Treatment of (IMes)3Fe4S4Cl with NaBAr F 4 in ethereal solvents (Et2O and THF) leads to the formation of an ether adduct, [(IMes)3Fe4S4(solv)][BAr F 4]; solvent can be displaced by addition of t BuNC to form the unusual mono-isocyanide adduct [(IMes)3Fe4S4(CN t Bu)][BAr F 4]. Carrying out the same reactions with the less sterically encumbered cluster (I i Pr Me)3Fe4S4Cl results in more typical reactivity: undesired ligand redistribution to form the homoleptic cluster [(I i Pr Me)4Fe4S4][BAr F 4] and generation of the tri-isocyanide adduct [(I i Pr Me)3Fe4S4(CN t Bu)3][BAr F 4]. The increased steric profile of the IMes ligands disfavors ligand redistribution and defines a binding pocket at the apical Fe, thereby enabling the generation of a coordinatively unsaturated and substitutionally labile Fe site. This method of controlling the coordination chemistry at the apical Fe site by modifying the sterics of ligands bound to adjacent Fe sites complements existing strategies for generating sitedifferentiated Fe-S clusters and provides new opportunities to direct reactivity at cuboidal metalloclusters.

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Section: Resultsmentioning

confidence: 82%

Section: Resultsmentioning

confidence: 99%

Controlling Substrate Binding to Fe₄S₄ Clusters through Remote Steric Effects

Brown

Suess

2019

Inorg. Chem.

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“…Molybdenum(IV) centers are known to bind both CO and Bu t NC [72,73,74,75]. Isocyanides also bind to the iron centers of Fe-S cubanes and similar clusters [76,77]. However, very interesting structural and mechanistic results relevant to nitrogen ®xation involving the reaction of isocyanides with cyclopentadienyl-capped di-molybdenum(IV) sul®do-bridged clusters, as carried out by DuBois and her collaborators [78,79], can be applied to this question.…”

Section: Discussionmentioning

confidence: 99%

Determination of ligand binding constants for the iron-molybdenum cofactor of nitrogenase: monomers, multimers, and cooperative behavior

Frank

Angove

Burgess

2001

J. Biol. Inorg. Chem.

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Equilibrium titrations in N-methylformamide (NMF) of G-25 gel filtered (ox)-state FeMo cofactor [FeMoco(ox)] from Azotobacter vinelandii nitrogenase were carried out using sodium ethanethiolate and followed using UV/Vis absorption spectroscopy. For Fe-Moco(ox), a non-linear least squares (NLLSQ) fit to the data indicated a strong equilibrium thiolate-binding step with Keq = 1.3+/-0.2x10(6) M(-1). With 245 molar excess imidazole, cooperative binding of three ethanethiolates was observed. The best NLLSQ fit gave Keq=2.0+/-0.1x10(5) M(-2) and a Hill coefficient n=2.0+/-0.3. A Scatchard plot of these data was concave upward, indicating positive cooperativity. The fit to previously published data involving benzenethiol titration of the one-electron reduced (semi-reduced) cofactor, FeMoco(sr), as followed by EPR required a model that included both a sub-stoichiometric ratio of thiol to FeMoco(sr) and about five cooperative ligand binding sites. These constraints were met by modeling FeMoco(sr) as an aggregate, with fewer thiol binding sites than FeMoco(sr) units. The best fit model was that of FeMoco(sr) as a dodecamer with five cooperative benzenethiol binding sites, yielding a thiol binding constant of 3.32+/-0.09x10(4) M(-4.8) and a Hill coefficient n=4.8+/-0.6. The results of all the other published ligand titrations of FeMoco(sr) were similarly analyzed successfully in terms of equilibrium models that include both cooperative ligand binding and dimer-level aggregation. A possible structural model for FeMoco aggregation in NMF solution is proposed.

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“…Whilst such a bonding mode has been found in some dinuclear coordination compounds of Mo,13a Re,13b Fe,13c Ru,13d–13f Rh,13g Pt,13h and other metals, this is unprecedented for double‐cubane structures. However, numerous examples of bridging S ligands are found in the [Fe 4 S 4 ] and FeMoS clusters, studied extensively by Holm et al and Coucouvanis et al, including sulfide or disulfide,14a–14c alkyl thiolates,14d,14e and 1,2‐ethane‐dithiolates 14f,14g…”

Section: Methodsmentioning

confidence: 99%

C−S Bond Cleavage and C−C Coupling in Cyclopentadienylchromium Complexes To Give the First Dithiooxamide-Bridged and Doubly Dithiocarbamate-Bridged Double Cubanes: [Cp6Cr8S8{(C(S)NEt2)2}] and [Cp6Cr8S8(S2CNEt2)2]

et al. 2001

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There have been extensive studies on the use of the dithiocarbamate ligand in a variety of bonding modes for stabilizing a wide range of oxidation states in coordination compounds of main-group and transition metals. [1] Although generally unreactive in the majority of its complexes, this ligand can undergo CÀS bond cleavage, a phenomenon first observed in a Mo complex in 1972 and becoming increasingly common in the last two decades. [2] In most cases, the cleaved S atom takes on a distinctly different coordination role in the complex, except where it is abstracted by an S acceptor such as PEt 3 . [2c] For example, the cleaved S atom can assume a bridging mode (M-S-M), [2a,b,f, 3] form an MS bond, [2d,g] or interact with a neighboring ligand (e.g., the MC bond of a coordinated alkyne). [2e] Cleavage of both CÀS bonds of the ligand was reported for reactions with [Ru 3 (CO) 12 ] [2h] and [Mo 2 (m-O 2 CMe) 4 ]. [3] Other reactions of the dithiocarbamate ligand include oxidative addition of a C À S bond to alkynes [4] and coupling reactions with coordinated alkyne, [2c, 5] alkylidene, [6] vinylidene/allenylidene, [7] and cyanide [8] ligands. Most of these studies involved Mo and W complexes, except for a few examples containing Cu, [4d] Nb and Ta, [2g] and Ru. [2h, 7] In the course of our investigations on the reactivity of [{CpCr(CO) 3 } 2 ] (Cp h 5 -C 5 H 5 ) towards the EÀE bonds of organic substrates such as diphenyl dichalcogenides Ph 2 E 2 (E S, Se, Te), [9] and bis(diphenylthiophosphinyl)disulfane [Ph 2 P(S)S] 2 , [10] we studied reactions with tetraalkylthiuram disulfides [R 2 NC(S)S] 2 , and here we report the first organochromium complexes containing dithiocarbamate and dithiooxamide ligands.The instantaneous reaction of [{CpCr(CO) 3 } 2 ] with one molar equivalent of tetraethylthiuram disulfide [Et 2 NC(S)S] 2 in toluene at ambient temperature gave a dark red solution, which upon concentration yielded air-stable deep red crystals of [CpCr(CO) 2 (S 2 CNEt 2 )] (1) in 87 % yield. A similar reaction at 90 8C for 2 h gave a dark brown mixture, from which were obtained, in order of elution from a silica gel column, the following compounds: [{CpCr(CO) 2 } 2 S] (7) as a dark green solid (ca. 1 % yield), (1) (22 % yield), [CpCr(CO) 2 (SCNEt 2 )] (2) as a dark red crystalline solid (11 % yield), [Cp 4 Cr 4 S 4 ] (3) as a dark solid (22 % yield), [Cp 6 Cr 8 S 8 {(C(S)NEt 2 ) 2 }] (4) as a brown solid (6.8 % yield), suggests stable trap site for the hole, the position of which is not far from the acceptor. The slow recombination of the geminate ion pair with the relatively short distance would be related to the trap-site structure or some sorts of reorganizations because of the charge shift in the PVCz film.

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The Mixed-Valence Double-Cubanoid Cluster [Fe₈S₁₂(Bu^tNC)₁₂]: Synthesis, Structure, and Exchange Coupling of a New Structural Array of Four Fe(III) Sites

Cited by 18 publications

References 29 publications

Controlling Substrate Binding to Fe₄S₄ Clusters through Remote Steric Effects

Controlling Substrate Binding to Fe₄S₄ Clusters through Remote Steric Effects

Determination of ligand binding constants for the iron-molybdenum cofactor of nitrogenase: monomers, multimers, and cooperative behavior

C−S Bond Cleavage and C−C Coupling in Cyclopentadienylchromium Complexes To Give the First Dithiooxamide-Bridged and Doubly Dithiocarbamate-Bridged Double Cubanes: [Cp6Cr8S8{(C(S)NEt2)2}] and [Cp6Cr8S8(S2CNEt2)2]

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The Mixed-Valence Double-Cubanoid Cluster [Fe8S12(ButNC)12]: Synthesis, Structure, and Exchange Coupling of a New Structural Array of Four Fe(III) Sites

Cited by 18 publications

References 29 publications

Controlling Substrate Binding to Fe4S4 Clusters through Remote Steric Effects

Controlling Substrate Binding to Fe4S4 Clusters through Remote Steric Effects

Determination of ligand binding constants for the iron-molybdenum cofactor of nitrogenase: monomers, multimers, and cooperative behavior

C−S Bond Cleavage and C−C Coupling in Cyclopentadienylchromium Complexes To Give the First Dithiooxamide-Bridged and Doubly Dithiocarbamate-Bridged Double Cubanes: [Cp6Cr8S8{(C(S)NEt2)2}] and [Cp6Cr8S8(S2CNEt2)2]

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The Mixed-Valence Double-Cubanoid Cluster [Fe₈S₁₂(Bu^tNC)₁₂]: Synthesis, Structure, and Exchange Coupling of a New Structural Array of Four Fe(III) Sites

Controlling Substrate Binding to Fe₄S₄ Clusters through Remote Steric Effects

Controlling Substrate Binding to Fe₄S₄ Clusters through Remote Steric Effects