Chloro(pyridine)cobaloxime

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Chloro(pyridine)cobaloxime(III)
Structure of Chloro(pyridine)cobaloxime fixed.png
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Names
Other names
Chloro(pyridine)bis(dimethylglyoximato)cobalt(III), Chloro(N,N'-dihydroxy-2,3-butanediimine-κ2N,N')(N-hydroxy-2,3-butanediiminato-κ2N,N')(methanol)cobalt - pyridine (1:1)
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.153.977 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 625-485-1
PubChem CID
Properties
C13H19ClCoN5O4
Molar mass 403.71 g·mol−1
Appearanceyellow-brown solid
insoluble
Hazards
GHS pictograms GHS-pictogram-exclam.svg
GHS Signal word Warning
H315, H319, H335
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Chloro(pyridine)cobaloxime is a coordination compound containing a CoIII center with octahedral coordination. It has been considered as a model compound of vitamin B12 for studying the properties and mechanism of action of the vitamin. It belongs to a class of bis(dimethylglyoximato)cobalt(III) complexes with different axial ligands, called cobaloximes. [1] Chloro(pyridine)cobaloxime is a yellow-brown powder that is sparingly soluble in most solvents, including water.

Contents

Structure

The complex adopts a distorted octahedral geometry. Cobalt(III) is bound to two dimethylglyoximate ligands, i.e., mono-deprotonated dimethylglyoxime, in the equatorial plane. Completing the coordination sphere are chloride and a pyridine at the axial positions. [2]

Reactions

The cobaloxime is slowly decomposed by acids and bases. With acids, the products of decomposition are dimethylglyoxime, cobalt salts, and pyridine; with bases, derivatives of other cobaloximes are formed, usually with the release of chloride ions.

The complex has no reaction with hydrogen gas, and cannot carry oxygen as salcomine does. It would, however, react with hydrogen in the presence of sodium hydroxide, a catalytic amount of platinum metal, or a reduced cobaloxime, therefore once the reduction occurs, the hydrogenation would occur much more rapidly as there is autocatalysis.

The reduction products of cobaloxime depends on the conditions. At pH near 7, a cobaloxime with a CoII center is formed. With a higher pH, the cobalt center would be further reduced to the CoI state, which is supernucleophilic. [3]

Preparation

The compound is usually prepared by mixing cobalt(II) chloride, dimethylglyoxime and pyridine in an ethanolic solution. This process afford the cobaloxime(II), which is subsequently oxidized by the oxygen in air: [3]

4 CoCl2•6H2O + 8 dmgH2 + 8 py + O2 → 4 ClCo(dmgH)2py + 4 py•HCl + 14 H2O

Using cobalt(II) acetate in place of cobalt(II) chloride produce aceto(pyridine)cobaloxime. This acetate can be converted to the respective bromide, iodide, cyanate, cyanide, azide and thiocyanate. [3]

(CH3COO)Co(DH)2py + NaX → XCo(DH)2py + NaCH3COO (X = Br, I, CNO, CN, N3 or SCN)

Reactions

The pyridine base in the axial position can also be replaced by other organic bases containing a sp2 hybridized N atom as well. Commonly used bases are morpholine, 4-methylpyridine, imidazole and benzimidazole. The derivatives are again prepared via diacetocobaloxime, followed by the addition of the desired base, such as imidazole.

(CH3COO)2Co(DH)2 + imi → (CH3COO)Co(DH)2imi

Alkylation of Co

One of the methods used for producing the Co-C bond is to make use of the supernucleophilicity of the CoI center. Chloro(pyridine)cobaloxime(III) is first reduced to Chloro(pyridine)cobaloxime(I) by sodium borohydride in alkaline solution, then an alkyl halide is added into the reaction mixture, and the desired Co-C bond is formed via a SN2 reaction. This method can be used to produce cobaloximes containing a primary or a secondary alkyl substituent.

For derivatives with phenyl or vinyl substituent, the Grignard reaction is employed. However, since the dimethylglyoxime ligands contains two acidic H atoms in the oxime group, the Grignard reagent must be used in three-fold excess to compensate the loss. [3]

Related Research Articles

Cobalt(II) chloride

Cobalt(II) chloride is an inorganic compound of cobalt and chlorine, with the formula CoCl
2. It is a sky blue crystalline solid.

Copper(II) chloride

Copper(II) chloride is the chemical compound with the chemical formula CuCl2. This is a light brown solid, which slowly absorbs moisture to form a blue-green dihydrate.

Wilkinsons catalyst Chemical compound

Wilkinson's catalyst is the common name for chloridotris(triphenylphosphine)rhodium(I), a coordination complex of rhodium with the formula [RhCl(PPh3)3] (Ph = phenyl). It is a red-brown colored solid that is soluble in hydrocarbon solvents such as benzene, and more so in tetrahydrofuran or chlorinated solvents such as dichloromethane. The compound is widely used as a catalyst for hydrogenation of alkenes. It is named after chemist and Nobel laureate Sir Geoffrey Wilkinson, who first popularized its use.

Rhodium(III) chloride

Rhodium(III) chloride refers to inorganic compounds with the formula RhCl3(H2O)n, where n varies from 0 to 3. These are diamagnetic solids featuring octahedral Rh(III) centres. Depending on the value of n, the material is either a dense brown solid or a soluble reddish salt. The soluble trihydrated (n = 3) salt is widely used to prepare compounds used in homogeneous catalysis, notably for the industrial production of acetic acid and hydroformylation.

Metal ammine complex

In coordination chemistry, metal ammine complexes are metal complexes containing at least one ammonia (NH3) ligand. "Ammine" is spelled this way due to historical reasons; in contrast, alkyl or aryl bearing ligands are spelt with a single "m". Almost all metal ions bind ammonia as a ligand, but the most prevalent examples of ammine complexes are for Cr(III), Co(III), Ni(II), Cu(II) as well as several platinum group metals.

Salen ligand

Salen refers to a tetradentate C2-symmetric ligand synthesized from salicylaldehyde (sal) and ethylenediamine (en). It may also refer to a class of compounds, which are structurally related to the classical salen ligand, primarily bis-Schiff bases. Salen ligands are notable for coordinating a wide range of different metals, which they can often stabilise in various oxidation states. These metal salen complexes primarily find use as catalysts.

Dimethylglyoxime

Dimethylglyoxime is a chemical compound described by the formula CH3C(NOH)C(NOH)CH3. Its abbreviation is dmgH2 for neutral form, and dmgH for anionic form, where H stands for hydrogen. This colourless solid is the dioxime derivative of the diketone butane-2,3-dione (also known as diacetyl). DmgH2 is used in the analysis of palladium or nickel. Its coordination complexes are of theoretical interest as models for enzymes and as catalysts. Many related ligands can be prepared from other diketones, e.g. benzil.

Hexamminecobalt(III) chloride

Hexaamminecobalt(III) chloride is the chemical compound with the formula [Co(NH3)6]Cl3. It is the chloride salt of the coordination complex [Co(NH3)6]3+, which is considered an archetypal "Werner complex", named after the pioneer of coordination chemistry, Alfred Werner. The cation itself is a metal ammine complex with six ammonia ligands attached to the cobalt(III) ion.

Iron(III) acetate

Ferric acetate is the acetate salt of the coordination complex [Fe3O(OAc)6(H2O)3]+ (OAc− is CH3CO2−). Commonly the salt is known as "basic iron acetate". The formation of the red-brown complex was once used as a test for ferric ions.

Cyclooctadiene rhodium chloride dimer

Cyclooctadiene rhodium chloride dimer is the organorhodium compound with the formula Rh2Cl2(C8H12)2, commonly abbreviated [RhCl(COD)]2 or Rh2Cl2(COD)2. This yellow-orange, air-stable compound is a widely used precursor to homogeneous catalysts.

Organoiridium compound

Organoiridium chemistry is the chemistry of organometallic compounds containing an iridium-carbon chemical bond. Organoiridium compounds are relevant to many important processes including olefin hydrogenation and the industrial synthesis of acetic acid. They are also of great academic interest because of the diversity of the reactions and their relevance to the synthesis of fine chemicals.

4-Toluenesulfonyl chloride

4-Toluenesulfonyl chloride (p-toluenesulfonyl chloride, toluene-p-sulfonyl chloride) is an organic compound with the formula CH3C6H4SO2Cl. This white, malodorous solid is a reagent widely used in organic synthesis. Abbreviated TsCl or TosCl, it is a derivative of toluene and contains a sulfonyl chloride (−SO2Cl) functional group.

Organorhodium chemistry

Organorhodium chemistry is the chemistry of organometallic compounds containing a rhodium-carbon chemical bond, and the study of rhodium and rhodium compounds as catalysts in organic reactions.

Chloropentamminecobalt chloride

Chloropentamminecobalt chloride is the dichloride salt of the coordination complex [Co(NH3)5Cl]2+. It is a red-violet, diamagnetic, water-soluble salt. The compound has been of academic and historical interest.

Pentaamminechlororhodium dichloride

Pentamminechlororhodium dichloride is the dichloride salt of the coordination complex [RhCl(NH3)5]2+. It is a yellow, water-soluble solid. The salt is an intermediate in the purification of rhodium from its ores.

Transition metal nitrile complexes

Transition metal nitrile complexes are coordination compounds containing nitrile ligands. Because nitriles are weakly basic, the nitrile ligands in these complexes are often labile.

Bis(triphenylphosphine)rhodium carbonyl chloride

Bis(triphenylphosphine)rhodium carbonyl chloride is the organorhodium complex with the formula [RhCl(CO)(PPh3)2]. This complex of rhodium(I) is a bright yellow, air-stable solid. It is the Rh analogue of Vaska's complex, the corresponding iridium complex. With regards to its structure, the complex is square planar with mutually trans triphenylphosphine (PPh3) ligands. The complex is a versatile homogeneous catalyst.

Dichlorotetrakis(pyridine)rhodium(III) chloride

Dichlorotetrakis(pyridine)rhodium(III) chloride is the chloride salt of the coordination complex with the formula [RhCl2(pyridine)4]+. It is a yellow solid that crystallizes from water as the tetrahydrate, which converts to the monohydrate upon vacuum drying at 100 °C. It is prepared by treating rhodium trichloride with an excess of pyridine in the presence of a catalytic amount of a reductant.

Transition metal pyridine complexes

Transition metal pyridine complexes encompas many coordination complexess that contain pyridine as a ligand. Most examples are mixed-ligand complexes. Many variants of pyridine are also known to coordinate to metal ions, such as the methylpyridines, quinolines, and more complex rings.

Transition metal chloride complex Coordination complex

In chemistry, a transition metal chloride complex is a coordination complex that consists of a transition metal coordinated to one or more chloride ligand. The class of complexes is extensive.

References

  1. ↑ Jonathan W. Steed; Jerry L. Atwood (2009). Supramolecular Chemistry, 2nd edition . Wiley. p.  808. ISBN   978-0-470-51233-3.
  2. ↑ Geremia, Silvano; Dreos, Renata; Randaccio, Lucio; Tauzher, Giovanni (February 1994). "Evidence of the interaction between steric and electronic influence in rhodoximes and cobaloximes. Syntehsis of pyRh(DH)2I and X-ray structure of pyRh(DH)2Cl and pyRh(DH)2I". Inorganica Chimica Acta. Trieste, Italy: Elsevier B.V. 216 (1–2): 125–129. doi:10.1016/0020-1693(93)03708-I.
  3. 1 2 3 4 G. N. Schrauzer (1968). "Bis(dimethylglyoximato)cobalt complexes (Cobaloximes) - A. Chloro(pyridine)cobaloxime(III)". Inorganic Syntheses. XI: 62–64. doi: 10.1002/9780470132425 . ISBN   9780470132425.
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