Michelle Millar

Synthesis and study of an analogue for the [Fe4S4]3+ center of oxidized high-potential iron-sulfur proteins

Etudes chimique et electrochimique qui montrent que le couple redox [Fe 4 S 4 (S-2,4,6-(i-Pr) 3 C 6 H 2 ) 4 ] 2− et [Fe 4 S 4 (S-2,3,5,6Me 4 C 6 H) 4 ] 2− est reversible. Synthese, structure et caracterisation spectroscopique du compose [Fe 4 S 4 (S-2,4,6-(iPr) 3 C 6 H 2 )] 4 (Bu 4 N) renfermant le site [Fe 4 S 4 ] 3+

X-ray crystal structures of a series of [MII(SR)4]2− complexes (MMn, Fe, Co, Ni, Zn, Cd and Hg) with S4 crystallographic symmetry

Abstract The X-ray crystal structures of an isomorphous and isostructural series of compounds, M(II) tetrathiolate complexes, [Et4N]2[M(S-2-Ph-C6H4)4]·2CH3CN (MMn, Fe, Co, Ni, Zn, Cd, Hg) are determined. The compounds crystallize in the tetragonal space group I 4 c2 (No. 120), which imposes S4 crystallographic symmetry on the [M(S-2-Ph-C6H4)4]2− anions. Each of the [M(S-2-Ph-C6H4)4]2− anions have tetragonally compressed [MS4] cores. The structures of this series of complexes add to the structural analysis of conformational isomers of [M(SAr)4]2−/1− complexes which are significant as models for [M(II)-(S-cys)4] centers in proteins.

Synthesis and Structure of Analogues for the Ni-Fe Site in Hydrogenase Enzymes

Dithiolate bridging Ni-Fe complexes [(dppe)Ni(II)(mu-SEt)(2)Fe(II)(CN)(2)(CO)(2)](6) and [(dppe)Ni(II)(mu-pdt)Fe(II)(CN)(2)(CO)(2)] [dppe = 1,2-bis(diphenylphosphino)ethane and pdt = 1,3-propanedithiolate] have been synthesized and structurally characterized as structural analogues of the active site of Ni-Fe hydrogenase enzymes. The synthesis starts from key intermediate fac-[Fe(CN)(2)(CO)(3)I](-). [(dppe)Ni(II)(mu-SEt)(2)Fe(II)(CN)(2)(CO)(2)](6), which features a near-planar diethanethiolate-bridged Ni-Fe rhomb, and the arrangement of 2CN(-) ligands is cis to each other. In contrast, [(dppe)Ni(II)(mu-pdt)Fe(II)(CN)(2)(CO)(2)] shows a much more folded NiS(2)Fe rhomb, a short Ni-Fe distance, trans 2CN(-) ligands, and a semibridging CN(-) between Ni and Fe.

Models for the iron-sulfur protein rubredoxin: the use of sterically hindered thiolate ligands to stabilize [Fe(SR)4]1− complexes; some considerations of the structure of the [Fe(S-Cys)4] centers in oxidized rubredoxins

Abstract Sterically hindered aromatic thiolate ligands have been used to synthesize the first examples of [FeIII(SR)4]1− complexes with monodentate ligands. The reaction of FeCl3 with 4 equiv. of lithium 2,3,5,6-tetramethylbenzenethiolate, Li[S-2,3,5,6-Me4C6H], lithium 2,4,6-triisopropylbenzenethiolate, Li[S-2,4,6-i-Pr3CC6H2] and the appropriate cation gives high yields of [Et4N][Fe(S-2,3,5,6-Me4C6H)4] (1) and [Ph4P][Fe(S-2,4,6-i-Pr3C6H2)4], respectively (2). Compounds 1 and 2 were structurally characterized by X-ray diffraction giving the crystallographic parameters: for 1, tetragonal space group I 4 with a = b = 12.366(2), c = 16.352(4) A , V = 2500 A 3 , Z = 2 ; for 2, triclinic space groups P 1 with a = 14.709(2); b = 20.928(5); c = 13.901(2) A , α = 90.97(3)°, β = 105.43(3)°, γ = 78.13(3)°, V = 4033 A 3 . The crystallographic symmetry of [Et4N][Fe(S-2,3,5,6-Me4C6H)4] requires the entire [Fe(SR)4]1−1 anion to have S4 point group symmetry and the [FeS[in4] core to have D2d symmetry. [Ph4P][Fe(S-2,4,6-i-Pr3C6H2)4]) possesses no crystallographi or apparent symmetry. It is suggested that the ability of the sterically hindered thiolate ligand to inhibit the autoredox reaction [ described by: Fe(III)SR → Fe(III) + 1 2 RSSR ] is due to the reduced tendency of these thiolates to bridge metal centers. Attention is drawn to the high idealized D2d symmetry of the [FeS4] cores and the [Fe(SCH2-)4] units of oxidized rubredoxins which are conserved in five different rubredoxins.

Synthesis and structure of titanium tetrathiolate and tantalum pentathiolate complexes. Metal-sulfur bonding in early transition metal compounds☆

The reaction of TiCl4 with potassium 2,3,5,6-tetramethylbenzenethiolate (KS-2,3,5,6-Me4C6H) in THF gives [Ti(S-2,3,5,6-Me4C6H)4] (1) in 50% yield. Compound 1 crystallizes in the triclinic space group P1 with a = 11.666(4), b = 19.417(5), c = 8.916(7)A, α = 97.09(2), β = 110.30(2), γ = 87.95(3)°, V =1880(3), A3, Z = 2. The monomeric [Ti(S-2,3,5,6-Me4C6H)4] has a distorted tetrahedral structure with TiS bonds of 2.292(6) A. One of the thiolate groups has a very acute MSC angle of 86.5(5)°. The reaction of TaCl5 with excess (LiS-2,3,5,6-Me4C6H) in hexane gives [Ta(S-2,3,5,6-Me4C6H)5] (2). Compound 2 crystallizes in the triclinic space group, P1 with a = 11.165(9), b = 18.675(11) A, α = 90.87(4), β = 101.83(6), γ = 96.77(5)°, V = 2407(5) A3 with Z = 2. [Ta(S-2,3,5,6-Me4C6H)5) is a monomeric compound with a distorted five-coordinate geometry. The average TaS bond distance is 2.37(3) A and TaSCav angle is 116(7)°. Structural comparisons of 1 and 2 with analogous phenolate complexes reveal large values for Δ[(MS)−(MO)]. The extent of the S to M gp-bonding in these electron deficient early transition metal thiolates is considerably reduced compared to the O to M π-bonding in phenolate analogs. The observation of the acute TiSC angles suggests that the limited thiolate metal π-bonding in 1 can not compensate for the strong electron deficiency of the Ti(IV) center.

Synthesis and structure of a unique nickel-thiolate dimer, [(RS)Ni(µ2-SR)3Ni(SR)]1–. An example of face-sharing bitetrahedra

The reaction of Ni(OAc)2 with Li[S-2,4,5-Pri3C6H2] and [Ph4P]Br in a 1 : 5 : 1 ratio produces [PPh4][Ni2(S-2,4,5-Pri3-C6H2)5]1; the anion of 1 was shown by X-ray crystallography to possess the rare face-sharing bitetrahedral geometry—the face-sharing [Ni(µ2-SR)3Ni] unit is described by acute Ni–S–Ni angles of 69° and a short Ni–Ni interaction of 2.607 A.