Transition metal thiolate complex

Last updated

Transition metal thiolate complexes are metal complexes containing thiolate ligands. Thiolates are ligands that can be classified as soft Lewis bases. Therefore, thiolate ligands coordinate most strongly to metals that behave as soft Lewis acids as opposed to those that behave as hard Lewis acids. Most complexes contain other ligands in addition to thiolate, but many homoleptic complexes are known with only thiolate ligands. The amino acid cysteine has a thiol functional group, consequently many cofactors in proteins and enzymes feature cysteinate-metal cofactors. [1]

Contents

The zinc finger motif, which is found in transcription factors, is a metal thiolate complex. Zinc finger rendered.png
The zinc finger motif, which is found in transcription factors, is a metal thiolate complex.
Structure of [Fe4S4(SMe)4] , a synthetic analogue of 4Fe-4S cofactors. OBINIX2.png
Structure of [Fe4S4(SMe)4] , a synthetic analogue of 4Fe-4S cofactors.

Synthesis

Metal thiolate complexes are commonly prepared by reactions of metal complexes with thiols (RSH), thiolates (RS−), and disulfides (R2S2). The salt metathesis reaction route is common. In this method, an alkali metal thiolate is treated with a transition metal halide to produce an alkali metal halide and the metal thiolate complex:

LiSC6H5 + CuI → Cu(SC6H5) + LiI

Lithium tert-butylthiolate reacts with MoCl4 to give the tetrathiolate complex: [3]

MoCl4 + 4 t-BuSLi → Mo(t-BuS)4 + 4 LiCl

Mo(t-BuS)4 is a dark red diamagnetic complex that is sensitive to air and moisture. The molybdenum center has a distorted tetrahedral coordination to four sulfur atoms, with overall D2 symmetry. [3]

Mo(t-BuS)4. Mo(t-BuS)4.png
Mo(t-BuS)4.

Nickelocene and ethanethiol give a dimeric thiolate, one cyclopentadienyl ligand serving as a base:

2 HSC2H5 + 2 Ni(C5H5)2 → [Ni(SC2H5)(C5H5)]2 + 2 C5H6
Thiomersal, a disinfectant, is a metal thiolate complex, being derived from Hg(II) and thiosalicylic acid. Thiomersal-Skeletal-Structure-SVG.svg
Thiomersal, a disinfectant, is a metal thiolate complex, being derived from Hg(II) and thiosalicylic acid.

Regarding their mechanism of formation from thiols, metal thiolate complexes can arise via deprotonation of thiol complexes. [4] [5]

Redox routes

Many thiolate complexes are prepared by redox reactions. Organic disulfides oxidize low valence metals, as illustrated by the oxidation of titanocene dicarbonyl:

(C5H5)2Ti(CO)2 + (C6H5S)2 → (C5H5)2Ti(SC6H5)2 + 2 CO

Some metal centers are oxidized by thiols, the coproduct being hydrogen gas:

Fe3(CO)12 + 2 C2H5SH → Fe2(SC2H5)2(CO)6 + Fe(CO)5 + CO + H2

These reactions may proceed by the oxidative addition of the thiol to Fe(0).

Thiols and especially thiolate salts are reducing agents. Consequently, they induce redox reactions with certain transition metals. This phenomenon is illustrated by the synthesis of cuprous thiolates from cupric precursors:

4 HSC6H5 + 2 CuO → 2 Cu(SC6H5) + (C6H5S)2 + 2 H2O

Thiolate clusters of the type [Fe4S4(SR)4]2− occur in iron–sulfur proteins. Synthetic analogues can be prepared by combined redox and salt metathesis reactions: [6]

4 FeCl3 + 6 NaSR + 6 NaSH → Na2[Fe4S4(SR)4] + 10 NaCl + 4 HCl + H2S + R2S2

Structure

Divalent sulfur exhibits bond angles approaching 90°. Such acute angles are also seen in the M-S-C angles of metal thiolates. Having filled p-orbitals of suitable symmetry, thiolates are pi-donor ligands. This property plays a role in the stabilization of Fe(IV) states in the enzyme cytochrome P450.

Structure of the quasi-two-coordinate ferrous dithiolate Fe[SC6H3-2,6-(C6H2-2,4,6-( Pr)3)2]2. A weak Fe-C(ipso) bond is indicated by the Fe---C distance of 2.427(1) A. The structure illustrates the low coordination numbers enabled by bulky ligands. JARKAP.png
Structure of the quasi-two-coordinate ferrous dithiolate Fe[SC6H3-2,6-(C6H2-2,4,6-( Pr)3)2]2. A weak Fe-C(ipso) bond is indicated by the Fe---C distance of 2.427(1) Å. The structure illustrates the low coordination numbers enabled by bulky ligands.

Reactions

Thiolates are relatively basic ligands, being derived from conjugate acids with pKa's of 6.5 (thiophenol) to 10.5 (butanethiol). Consequently, thiolate ligand often bridge pairs of metals. One example is Fe2(SCH3)2(CO)6. Thiolate ligands, especially when nonbridging, are susceptible to attack by electrophiles including acids, alkylating agents, and oxidants.

Structure of Fe2(SCH3)2(CO)6. Fe2 SMe 2 CO 6.svg
Structure of Fe2(SCH3)2(CO)6.

Occurrence and applications

Metal thiolate functionality is pervasive in metalloenzymes. Iron-sulfur proteins, blue copper proteins, and the zinc-containing enzyme liver alcohol dehydrogenase feature thiolate ligands. Commonly thiolate is ligand is provided from the cysteine residue. All molybdoproteins feature thiolates in the form of cysteinyl and/or molybdopterin. [8]

The copper site in plastocyanin features two imidazole, a thioether, and a thiolate ligand. Plastocyanin copper binding.png
The copper site in plastocyanin features two imidazole, a thioether, and a thiolate ligand.

Related Research Articles

In biochemistry, a disulfide refers to a functional group with the structure R−S−S−R′. The linkage is also called an SS-bond or sometimes a disulfide bridge and is usually derived by the coupling of two thiol groups. In biology, disulfide bridges formed between thiol groups in two cysteine residues are an important component of the secondary and tertiary structure of proteins. Persulfide usually refers to R−S−S−H compounds.

<span class="mw-page-title-main">Iron–sulfur cluster</span> Class of molecules

Iron–sulfur clusters are molecular ensembles of iron and sulfide. They are most often discussed in the context of the biological role for iron–sulfur proteins, which are pervasive. Many Fe–S clusters are known in the area of organometallic chemistry and as precursors to synthetic analogues of the biological clusters. It is believed that the last universal common ancestor had many iron-sulfur clusters.

<span class="mw-page-title-main">Metalloprotein</span> Protein that contains a metal ion cofactor

Metalloprotein is a generic term for a protein that contains a metal ion cofactor. A large proportion of all proteins are part of this category. For instance, at least 1000 human proteins contain zinc-binding protein domains although there may be up to 3000 human zinc metalloproteins.

Iron(III) chloride describes the inorganic compounds with the formula FeCl3(H2O)x. Also called ferric chloride, these compounds are some of the most important and commonplace compounds of iron. They are available both in anhydrous and in hydrated forms which are both hygroscopic. They feature iron in its +3 oxidation state. The anhydrous derivative is a Lewis acid, while all forms are mild oxidizing agent. It is used as a water cleaner and as an etchant for metals.

Ferredoxins are iron–sulfur proteins that mediate electron transfer in a range of metabolic reactions. The term "ferredoxin" was coined by D.C. Wharton of the DuPont Co. and applied to the "iron protein" first purified in 1962 by Mortenson, Valentine, and Carnahan from the anaerobic bacterium Clostridium pasteurianum.

Iron–sulfur proteins are proteins characterized by the presence of iron–sulfur clusters containing sulfide-linked di-, tri-, and tetrairon centers in variable oxidation states. Iron–sulfur clusters are found in a variety of metalloproteins, such as the ferredoxins, as well as NADH dehydrogenase, hydrogenases, coenzyme Q – cytochrome c reductase, succinate – coenzyme Q reductase and nitrogenase. Iron–sulfur clusters are best known for their role in the oxidation-reduction reactions of electron transport in mitochondria and chloroplasts. Both Complex I and Complex II of oxidative phosphorylation have multiple Fe–S clusters. They have many other functions including catalysis as illustrated by aconitase, generation of radicals as illustrated by SAM-dependent enzymes, and as sulfur donors in the biosynthesis of lipoic acid and biotin. Additionally, some Fe–S proteins regulate gene expression. Fe–S proteins are vulnerable to attack by biogenic nitric oxide, forming dinitrosyl iron complexes. In most Fe–S proteins, the terminal ligands on Fe are thiolate, but exceptions exist.

<span class="mw-page-title-main">Thiophenol</span> Chemical compound

Thiophenol is an organosulfur compound with the formula C6H5SH, sometimes abbreviated as PhSH. This foul-smelling colorless liquid is the simplest aromatic thiol. The chemical structures of thiophenol and its derivatives are analogous to phenols. An exception is the oxygen atom in the hydroxyl group (-OH) bonded to the aromatic ring is replaced by a sulfur atom. The prefix thio- implies a sulfur-containing compound and when used before a root word name for a compound which would normally contain an oxygen atom, in the case of 'thiol' that the alcohol oxygen atom is replaced by a sulfur atom.

<span class="mw-page-title-main">Metal dithiolene complex</span>

Dithiolene metal complexes are complexes containing 1,2-dithiolene ligands. 1,2-Dithiolene ligands, a particular case of 1,2-dichalcogenolene species along with 1,2-diselenolene derivatives, are unsaturated bidentate ligand wherein the two donor atoms are sulfur. 1,2-Dithiolene metal complexes are often referred to as "metal dithiolenes", "metallodithiolenes" or "dithiolene complexes". Most molybdenum- and tungsten-containing proteins have dithiolene-like moieties at their active sites, which feature the so-called molybdopterin cofactor bound to the Mo or W.

<span class="mw-page-title-main">Isopenicillin N synthase</span>

Isopenicillin N synthase (IPNS) is a non-heme iron protein belonging to the 2-oxoglutarate (2OG)-dependent dioxygenases oxidoreductase family. This enzyme catalyzes the formation of isopenicillin N from δ-(L-α-aminoadipoyl)-L-cysteinyl-D-valine (LLD-ACV).

<span class="mw-page-title-main">High potential iron–sulfur protein</span>

High potential iron-sulfur proteins (HIPIP) are a class of iron-sulfur proteins. They are ferredoxins that participate in electron transfer in photosynthetic bacteria as well as in Paracoccus denitrificans.

<span class="mw-page-title-main">Liebeskind–Srogl coupling</span>

The Liebeskind–Srogl coupling reaction is an organic reaction forming a new carbon–carbon bond from a thioester and a boronic acid using a metal catalyst. It is a cross-coupling reaction. This reaction was invented by and named after Jiri Srogl from the Academy of Sciences, Czech Republic, and Lanny S. Liebeskind from Emory University, Atlanta, Georgia, USA. There are three generations of this reaction, with the first generation shown below. The original transformation used catalytic Pd(0), TFP = tris(2-furyl)phosphine as an additional ligand and stoichiometric CuTC = copper(I) thiophene-2-carboxylate as a co-metal catalyst. The overall reaction scheme is shown below.

In organometallic chemistry, bent metallocenes are a subset of metallocenes. In bent metallocenes, the ring systems coordinated to the metal are not parallel, but are tilted at an angle. A common example of a bent metallocene is Cp2TiCl2. Several reagents and much research is based on bent metallocenes.

<span class="mw-page-title-main">Titanocene pentasulfide</span> Chemical compound

Titanocene pentasulfide is the organotitanium compound with the formula (C5H5)2TiS5, commonly abbreviated as Cp2TiS5. This metallocene exists as a bright red solid that is soluble in organic solvents. It is of academic interest as a precursor to unusual allotropes of elemental sulfur as well as some related inorganic rings.

[NiFe] hydrogenase is a type of hydrogenase, which is an oxidative enzyme that reversibly converts molecular hydrogen in prokaryotes including Bacteria and Archaea. The catalytic site on the enzyme provides simple hydrogen-metabolizing microorganisms a redox mechanism by which to store and utilize energy via the reaction

In organometallic chemistry, a transition metal alkene complex is a coordination compound containing one or more alkene ligands. The inventory is large. Such compounds are intermediates in many catalytic reactions that convert alkenes to other organic products.

<span class="mw-page-title-main">CO-methylating acetyl-CoA synthase</span> Enzyme

Acetyl-CoA synthase (ACS), not to be confused with acetyl-CoA synthetase or acetate-CoA ligase, is a nickel-containing enzyme involved in the metabolic processes of cells. Together with carbon monoxide dehydrogenase (CODH), it forms the bifunctional enzyme Acetyl-CoA Synthase/Carbon Monoxide Dehydrogenase (ACS/CODH) found in anaerobic organisms such as archaea and bacteria. The ACS/CODH enzyme works primarily through the Wood–Ljungdahl pathway which converts carbon dioxide to Acetyl-CoA. The recommended name for this enzyme is CO-methylating acetyl-CoA synthase.

Evolution of metal ions in biological systems refers to the incorporation of metallic ions into living organisms and how it has changed over time. Metal ions have been associated with biological systems for billions of years, but only in the last century have scientists began to truly appreciate the scale of their influence. Major and minor metal ions have become aligned with living organisms through the interplay of biogeochemical weathering and metabolic pathways involving the products of that weathering. The associated complexes have evolved over time.

<span class="mw-page-title-main">Metal cluster compound</span> Cluster of three or more metals

Metal cluster compounds are a molecular ion or neutral compound composed of three or more metals and featuring significant metal-metal interactions.

Julia A. Kovacs is an American chemist specializing in bioinorganic chemistry. She is professor of chemistry at the University of Washington. Her research involves synthesizing small-molecule mimics of the active sites of metalloproteins, in order to investigate how cysteinates influence the function of non-heme iron enzymes, and the mechanism of the oxygen-evolving complex (OEC).

<span class="mw-page-title-main">Transition metal nitrite complex</span> Chemical complexes containing one or more –NO₂ ligands

In organometallic chemistry, transition metal complexes of nitrite describes families of coordination complexes containing one or more nitrite ligands. Although the synthetic derivatives are only of scholarly interest, metal-nitrite complexes occur in several enzymes that participate in the nitrogen cycle.

References

  1. ↑ Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999), Advanced Inorganic Chemistry (6th ed.), New York: Wiley-Interscience, ISBN   0-471-19957-5
  2. ↑ Axel Kern; Christian Näther; Felix Studt; Felix Tuczek (2004). "Application of a Universal Force Field to Mixed Fe/Mo−S/Se Cubane and Heterocubane Clusters. 1. Substitution of Sulfur by Selenium in the Series [Fe4X4(YCH3)4]2-; X = S/Se and Y = S/Se". Inorg. Chem. 43 (16): 5003–5010. doi:10.1021/ic030347d. PMID   15285677.
  3. 1 2 Otsuka, Sei; Kamata, Masato; Hirotsu, Ken; Higuchi, Taiichi (1981). "A Novel Molybdenum Thiolato Compound, Tetrakis(tert-butylthiolato)molybdenum(IV). Preparation and Crystal and Molecular Structure". Journal of the American Chemical Society. 103 (11): 3011–3014. doi:10.1021/ja00401a017.
  4. ↑ Jessop, Philip G.; Morris, Robert H. (1993). "Hydrogen/Deuterium exchange reactions of an iridium dithiol complex". Inorganic Chemistry. 32 (11): 2236–2237. doi:10.1021/ic00063a006.
  5. ↑ Heller, M.; Sheldrick, W. S. (2004). "Copper(I) Coordination Polymers with Alkanedithiol and -dinitrile Bridging Ligands". Zeitschrift für anorganische und allgemeine Chemie. 630 (12): 1869–1874. doi:10.1002/zaac.200400165.
  6. ↑ Lee, S. C.; Lo, W.; Holm, R. H. (2014). "Developments in the Biomimetic Chemistry of Cubane-Type and Higher Nuclearity Iron–Sulfur Clusters". Chemical Reviews. 114 (7): 3579–3600. doi:10.1021/cr4004067. PMC   3982595 . PMID   24410527.
  7. ↑ Nguyen, T.; Panda, A.; Olmstead, M. M.; Richards, A. F.; Stender, M.; Brynda, M.; Power, P. P. (2005). "Synthesis and Characterization of Quasi-Two-Coordinate Transition Metal Dithiolates M(SAr)2 (M = Cr, Mn, Fe, Co, Ni, Zn; Ar = C6H3-2,6(C6H2-2,4,6-Pri3)2)". J. Am. Chem. Soc. 127 (23): 8545–8552. doi:10.1021/ja042958q. PMID   15941290.
  8. ↑ S. J. Lippard, J. M. Berg "Principles of Bioinorganic Chemistry" University Science Books: Mill Valley, CA; 1994. ISBN   0-935702-73-3.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.