Transition metal complexes of 2,2'-bipyridine

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Transition metal complexes of 2,2'-bipyridine are coordination complexes containing one or more 2,2'-bipyridine ligands. Complexes have been described for all of the transition metals. [ citation needed ] Although few have any practical value, these complexes have been influential. [1] 2,2'-Bipyridine is classified as a diimine ligand. Unlike the structures of pyridine complexes, the two rings in bipy are coplanar, which facilitates electron delocalization. As a consequence of this delocalization, bipy complexes often exhibit distinctive optical and redox properties.

Contents

Complexes

Bipy forms a wide variety of complexes. Almost always, it is a bidentate ligand, binding metal centers with the two nitrogen atoms. Examples:

Tris-bipy complexes

Three-dimensional view of the [Fe(bipy)3] complex. Fe-Bipy-3.png
Three-dimensional view of the [Fe(bipy)3] complex.

Bipyridine complexes absorb intensely in the visible part of the spectrum. The electronic transitions are attributed to metal-to-ligand charge transfer (MLCT). In the "tris(bipy) complexes" three bipyridine molecules coordinate to a metal ion, written as [M(bipy)3]n+ (M = metal ion; Cr, Fe, Co, Ru, Rh and so on). These complexes have six-coordinated, octahedral structures and exists as enantiomeric pairs:

Bpycomp.png

These and other homoleptic tris-2,2′-bipy complexes of many transition metals are electroactive. Often, both the metal centred and ligand centred electrochemical reactions are reversible one-electron reactions that can be observed by cyclic voltammetry. Under strongly reducing conditions, some tris(bipy) complexes can be reduced to neutral derivatives containing bipy− ligands. Examples include M(bipy)3, where M = Al, Cr, Si. [4]

Square planar complexes

Structure of [Pt(bipy)2] as determined by X-ray crystallography. (Pt(bipy)2)++ Xray JAXQOP.png
Structure of [Pt(bipy)2] as determined by X-ray crystallography.

Square planar complexes of the type [Pt(bipy)2]2+ react with nucleophiles because of the steric clash between the 6,6' positions between the pair of bipy ligands. This clash is indicated by the bowing of the pyridyl rings out of the plane defined by PtN4. [5]

Many ring-substituted variants of bipy have been described, especially dimethyl-2,2'-bipyridines. [6] [7] Alkyl substituents enhance the solubility of the complexes in organic solvents. 6,6'-Substituents tend to protect the metal center. [8]

The related N,N-heterocyclic ligand phenanthroline forms similar complexes. With respective pKa's of 4.86 and 4.3 for their conjugate acids, phenanthroline and bipy are of comparable basicity. [9]

2,2'-Biquinoline is closely related to bipy as a ligand.

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

Polypyridine complexes are coordination complexes containing polypyridine ligands, such as 2,2'-bipyridine, 1,10-phenanthroline, or 2,2';6'2"-terpyridine.

<span class="mw-page-title-main">Bipyridine</span> Group of chemical compounds

Bipyridines are a family of organic compounds with the formula (C5H4N)2, consisting of two pyridyl (C5H4N) rings. Pyridine is an aromatic nitrogen-containing heterocycle. The bipyridines are all colourless solids, which are soluble in organic solvents and slightly soluble in water. Bipyridines, especially the 4,4' isomer, are mainly of significance in pesticides.

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

Terpyridine is a heterocyclic compound derived from pyridine. It is a white solid that is soluble in most organic solvents. The compound is mainly used as a ligand in coordination chemistry.

<span class="mw-page-title-main">1,10-Phenanthroline</span> Heterocyclic organic compound

1,10-Phenanthroline (phen) is a heterocyclic organic compound. It is a white solid that is soluble in organic solvents. The 1,10 refer to the location of the nitrogen atoms that replace CH's in the hydrocarbon called phenanthrene.

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<span class="mw-page-title-main">Ruthenium(III) chloride</span> Chemical compound

Ruthenium(III) chloride is the chemical compound with the formula RuCl3. "Ruthenium(III) chloride" more commonly refers to the hydrate RuCl3·xH2O. Both the anhydrous and hydrated species are dark brown or black solids. The hydrate, with a varying proportion of water of crystallization, often approximating to a trihydrate, is a commonly used starting material in ruthenium chemistry.

<span class="mw-page-title-main">2,2′-Bipyridine</span> Chemical compound

2,2′-Bipyridine (bipy or bpy, pronounced ) is an organic compound with the formula C10H8N2. This colorless solid is an important isomer of the bipyridine family. It is a bidentate chelating ligand, forming complexes with many transition metals. Ruthenium and platinum complexes of bipy exhibit intense luminescence, which may have practical applications.

<span class="mw-page-title-main">Tris(bipyridine)ruthenium(II) chloride</span> Chemical compound

Tris(bipyridine)ruthenium(II) chloride is the chloride salt coordination complex with the formula [Ru(bpy)3]Cl2. This polypyridine complex is a red crystalline salt obtained as the hexahydrate, although all of the properties of interest are in the cation [Ru(bpy)3]2+, which has received much attention because of its distinctive optical properties. The chlorides can be replaced with other anions, such as PF6−.

In chemistry, a (redox) non-innocent ligand is a ligand in a metal complex where the oxidation state is not clear. Typically, complexes containing non-innocent ligands are redox active at mild potentials. The concept assumes that redox reactions in metal complexes are either metal or ligand localized, which is a simplification, albeit a useful one.

<span class="mw-page-title-main">Electrochemiluminescence</span> Emission of light from electrochemical reactions

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<span class="mw-page-title-main">Organoruthenium chemistry</span>

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<span class="mw-page-title-main">BTBP</span> A class of tetradentate ligand compounds

The bis-triazinyl bipyridines (BTBPs) are a class of chemical compounds which are tetradentate ligands similar in shape to quaterpyridine. The BTBPs are made by the reaction of hydrazine and a 1,2-diketone with 6,6'-dicyano-2,2'-bipyridine. The dicyanobipy can be made by reacting 2,2'-bipy with hydrogen peroxide in acetic acid, to form 2,2'-bipyridine-N,N-dioxide. The 2,2'-bipyridine-N,N-dioxide is then converted into the dicyano compound by treatment with potassium cyanide and benzoyl chloride in a mixture of water and THF.

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<span class="mw-page-title-main">Charge-transfer band</span> Characteristic feature of the optical spectra of many compounds

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<span class="mw-page-title-main">Photoredox catalysis</span>

Photoredox catalysis is a branch of photochemistry that uses single-electron transfer. Photoredox catalysts are generally drawn from three classes of materials: transition-metal complexes, organic dyes, and semiconductors. While organic photoredox catalysts were dominant throughout the 1990s and early 2000s, soluble transition-metal complexes are more commonly used today.

<i>cis</i>-Dichlorobis(bipyridine)ruthenium(II) Chemical compound

cis-Dichlorobis(bipyridine)ruthenium(II) is the coordination complex with the formula RuCl2(bipy)2, where bipy is 2,2'-bipyridine. It is a dark green diamagnetic solid that is a precursor to many other complexes of ruthenium, mainly by substitution of the two chloride ligands. The compound has been crystallized as diverse hydrates.

<span class="mw-page-title-main">Transition metal pyridine complexes</span>

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<span class="mw-page-title-main">Dichlororuthenium tricarbonyl dimer</span> Chemical compound

Dichlororuthenium tricarbonyl dimer is an organoruthenium compound with the formula [RuCl2(CO)3]2. A yellow solid, the molecule features a pair of octahedral Ru centers bridged by a pair of chloride ligands. The complex is a common starting material in ruthenium chemistry.

In inorganic chemistry, the Primogenic Effect describes the change in excited state manifolds for first row vs second and third row metal complexes. The effect is used to rationalize the ability or inability of certain metal complexes to function as photosensitizers, which in turn is relevant to photocatalysis.

<span class="mw-page-title-main">Tris(bipyridine)iron(II) chloride</span> Chemical compound

Tris(bipyridine)iron(II) chloride is the chloride salt of the coordination complex tris(bipyridine)iron(II), [Fe(C10H8N2)3]2+. It is a red solid. In contrast to tris(bipyridine)ruthenium(II), this iron complex is not a useful photosensitizer because its excited states relax too rapidly, a consequence of the primogenic effect.

References

  1. 1 2 Constable; Housecroft (2019). "The Early Years of 2,2'-Bipyridine—A Ligand in its Own Lifetime". Molecules. 24 (21): 3951. doi: 10.3390/molecules24213951 . PMC   6864536 . PMID   31683694.
  2. ↑ Lay, P. A.; Sargeson, A. M.; Taube, H.; Chou, M. H.; Creutz, C. (1986). "cis-Bis(2,2′-bipyridine-N,N′) Complexes of Ruthenium(III)/(II) and Osmium(III)/(II)". Inorganic Syntheses . 24: 291–299. doi:10.1002/9780470132555.ch78. ISBN   9780470132555.
  3. ↑ Concepcion, Javier J.; Jurss, Jonah W.; Templeton, Joseph L.; Meyer, Thomas J. (2008). "Mediator-Assisted Water Oxidation by the Ruthenium "Blue Dimer" cis,cis -[(bpy)2(H2O)RuORu(OH2)(bpy)2]4+". Proceedings of the National Academy of Sciences. 105 (46): 17632–17635. Bibcode:2008PNAS..10517632C. doi: 10.1073/pnas.0807153105 . PMID   19004763.
  4. ↑ Scarborough, Christopher C.; Wieghardt, Karl (2011). "Electronic Structure of 2,2′-Bipyridine Organotransition-Metal Complexes. Establishing the Ligand Oxidation Level by Density Functional Theoretical Calculations". Inorganic Chemistry. 50 (20): 9773–9793. doi:10.1021/ic2005419. PMID   21678919.
  5. 1 2 Clare, Bronya R.; McInnes, Claire S.; Blackman, Allan G. (2005). "Bis(2,2′-bipyridine-κ2N,N′)platinum(II) Bis(perchlorate)". Acta Crystallographica Section E. 61 (10): m2042–m2043. doi:10.1107/S1600536805029089.
  6. ↑ Smith, A. P.; Lamba, J. J. S.; Fraser, C. L. (2002). "Efficient Synthesis of Halomethyl-2,2′-Bipyridines: 4,4′-Bis(chloromethyl)-2,2′-Bipyridine". Organic Syntheses . 78: 82. doi:10.15227/orgsyn.078.0082 .
  7. ↑ Smith, A. P.; Savage, S. A.; Love, J.; Fraser, C. L. (2002). "Synthesis of 4-, 5-, and 6-Methyl-2,2′-Bipyridine by a Negishi Cross-Coupling Strategy". Organic Syntheses . 78: 51. doi:10.15227/orgsyn.078.0051 .
  8. ↑ Bhattacharya, Moumita; Sebghati, Sepehr; Vanderlinden, Ryan T.; Saouma, Caroline T. (2020). "Toward Combined Carbon Capture and Recycling: Addition of an Amine Alters Product Selectivity from CO to Formic Acid in Manganese Catalyzed Reduction of CO2". Journal of the American Chemical Society. 142 (41): 17589–17597. doi:10.1021/jacs.0c07763. PMC   7584391 . PMID   32955864.
  9. ↑ J. G. Leipoldt; G. J. Lamprecht; E. C.Steynberg (1991). "Kinetics of the Substitution of Acetylacetone in Acetylactonato-1,5-cyclooctadienerhodium(I) by Derivatives of 1,10-Phenanthroline and 2,2′-Dipyridyl". Journal of Organometallic Chemistry. 402 (2): 259–263. doi:10.1016/0022-328X(91)83069-G.
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