Metal Ion Incorporation Reactions of the Cluster [Fe₃S₄(LS₃)]^3-, Containing the Cuboidal [Fe₃S₄]⁰ Core

Abstract

The frequent occurrence of the cuboidal cluster [Fe3S4(S·Cys)3] in a variety of proteins has prompted extensive investigation of its chemical and biological properties. The biological function remains in question, but the cluster is known to sustain two reactions: (i) electron transfer, and (ii) heterometal ion incorporation. The recent preparation of [Fe3S4(LS3)]3- (3) [Zhou, J.; Hu, Z.; Münck, E.; Holm, R. H. J. Am. Chem. Soc. 1996, 118, 1966] has permitted detailed structural, electronic, and reactivity characterization of the cuboidal [Fe3S4]0 oxidation state (LS3 = 1,3,5-tris((4,6-dimethyl-3-mercaptophenyl)thio)-2,4,6-tris(p-tolylthio)benzene(3−). Redox properties (i) have been reported previously: here reaction type (ii), resulting in the formation of cubane-type MFe3S4 clusters, has been investigated. Reaction of 3 with [M(PPh3)4]1+ affords [(Ph3P)MFe3S4(LS3)]2- (M = Cu (6), Ag (8)) while [(NC)M(PPh3)3] leads to [(NC)MFe3S4(LS3)]3- (M = Cu (7), Ag (9)). Treatment of 3 with Tl(O3SCF3) yields [TlFe3S4(LS3)]2- (10). The fragment formalism {M1+ + [Fe3S4]0} applies to 6−10, which retain the S = 2 ground state of 3. Reaction of 3 with [M(PPh3)3Cl] yields [(Ph3P)MFe3S4(LS3)]2- (M = Co (12), Ni (14)) in inner-sphere redox reactions. Clusters 12 (S = 1) and 14 (S = 3/2) are formulated as {M2+ + [Fe3S4]1-}; antiferromagnetic coupling of fragment spins gives rise to the indicated spin ground states. The reactions (ii) are metal-ion incorporation processes, a new reaction type in Fe−S chemistry. Previously, all cubane-type MFe3S4 clusters had been synthesized by spontaneous self-assembly or reductive rearrangement reactions. Cluster 7 exhibits reversible oxidation and reduction reactions; it is the only cluster that forms a stable oxidized product containing the [Fe3S4]1+ fragment. All other clusters show a reversible reduction and an irreversible or quasireversible oxidation. Potentials of the synthetic clusters are considered intrinsic to the various core units, being less influenced by environmental factors than are those in proteins. At parity of cluster charge and terminal ligation, the potential order is M = Fe < Co < Ni and Co < Ni < Cu < Ag < Tl for the [MFe3S4]2+,1+ and [MFe3S4]1+,0 core redox reactions. These orders are compared with those determined in proteins.

Synthesis of MFe3S4Clusters Containing a Planar MIISite (M = Ni, Pd, Pt), a Structural Element in the C-Cluster of Carbon Monoxide Dehydrogenase

“…The structures of the five compounds listed in Table 1 [17]·1/2MeCN was formed during the attempted crystallization of 15 from acetonitrile. Data for crystals containing 3,16, and 17 were collected on a Siemens (Bruker) SMART CCD-based diffractometer.…”

Synthesis, crystal structures, Mössbauer spectra, and redox properties of binuclear and tetranuclear iron-sulfur nitrosyl clusters

“…3 In this connection, a search for hey, stable NO donors based on nitrosyl Fe--S clusters and studies of the relationship between their structures and reactivities are of interest. In spite of the diversity of the known (20 g), NaNO 2 (8 g).…”

Speculative synthetic chemistry and the nitrogenase problem

“…1). Synthetic methodology has kept pace with these developments: In addition to the thiometallate routes used for the early transition metal [MFe 3 S 4 ] clusters, pathways starting from trinuclear Fe-S clusters have allowed access to late metal derivatives as well (Scheme 2), and well defined, synthetic examples of the [MFe 3 S 4 ] cubane core are now known for M ϭ V, Nb, Mo, W, Re, Co, Ni, Cu, Ag, Tl (13,16). The accessibility, stability, and recurrence of the heterometallic cubane motif suggest that additional biological examples may surface in the future.…”