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. [3]

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. [4]

Many ring-substituted variants of bipy have been described, especially dimethyl-2,2'-bipyridines. [5] [6] Alkyl substituents enhance the solubility of the complexes in organic solvents. 6,6'-Substituents tend to protect the metal center. [7]

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. [8]

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

Related Research Articles

<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.

<span class="mw-page-title-main">Amidine</span> Organic compounds

Amidines are organic compounds with the functional group RC(NR)NR2, where the R groups can be the same or different. They are the imine derivatives of amides (RC(O)NR2). The simplest amidine is formamidine, HC(=NH)NH2.

<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.

<i>tert</i>-Butyllithium Chemical compound

tert-Butyllithium is a chemical compound with the formula (CH3)3CLi. As an organolithium compound, it has applications in organic synthesis since it is a strong base, capable of deprotonating many carbon molecules, including benzene. tert-Butyllithium is available commercially as hydrocarbon solutions; it is not usually prepared in the laboratory.

<span class="mw-page-title-main">Sandwich compound</span> Chemical compound made of two ring ligands bound to a metal

In organometallic chemistry, a sandwich compound is a chemical compound featuring a metal bound by haptic, covalent bonds to two arene (ring) ligands. The arenes have the formula CnHn, substituted derivatives and heterocyclic derivatives. Because the metal is usually situated between the two rings, it is said to be "sandwiched". A special class of sandwich complexes are the metallocenes.

<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−.

Silylation is the introduction of one or more (usually) substituted silyl groups (R3Si) to a molecule. Silylations are core methods for production of organosilicon chemistry. Silanization involves similar methods but usually refers to attachment of silyl groups to solids.

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

Oxazoline is a five-membered heterocyclic organic compound with the formula C3H5NO. It is the parent of a family of compounds called oxazolines, which contain non-hydrogenic substituents on carbon and/or nitrogen. Oxazolines are the unsaturated analogues of oxazolidines, and they are isomeric with isoxazolines, where the N and O are directly bonded. Two isomers of oxazoline are known, depending on the location of the double bond.

<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.

Metal acetylacetonates are coordination complexes derived from the acetylacetonate anion (CH
3COCHCOCH−
3) and metal ions, usually transition metals. The bidentate ligand acetylacetonate is often abbreviated acac. Typically both oxygen atoms bind to the metal to form a six-membered chelate ring. The simplest complexes have the formula M(acac)3 and M(acac)2. Mixed-ligand complexes, e.g. VO(acac)2, are also numerous. Variations of acetylacetonate have also been developed with myriad substituents in place of methyl (RCOCHCOR′−). Many such complexes are soluble in organic solvents, in contrast to the related metal halides. Because of these properties, acac complexes are sometimes used as catalyst precursors and reagents. Applications include their use as NMR "shift reagents" and as catalysts for organic synthesis, and precursors to industrial hydroformylation catalysts. C
5H
7O−
2 in some cases also binds to metals through the central carbon atom; this bonding mode is more common for the third-row transition metals such as platinum(II) and iridium(III).

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

A metal-phosphine complex is a coordination complex containing one or more phosphine ligands. Almost always, the phosphine is an organophosphine of the type R3P (R = alkyl, aryl). Metal phosphine complexes are useful in homogeneous catalysis. Prominent examples of metal phosphine complexes include Wilkinson's catalyst (Rh(PPh3)3Cl), Grubbs' catalyst, and tetrakis(triphenylphosphine)palladium(0).

<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">3,5-Dimethylpyrazole</span> Chemical compound

3,5-Dimethylpyrazole is an organic compound with the formula (CH3C)2CHN2H. It is one of several isomeric derivatives of pyrazole that contain two methyl substituents. The compound is unsymmetrical but the corresponding conjugate acid (pyrazolium) and conjugate base (pyrazolide) have C2v symmetry. It is a white solid that dissolves well in polar organic solvents.

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

Transition metal pyridine complexes encompass many coordination complexes 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.

<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. ↑ 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.
  4. 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.
  5. ↑ 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.
  6. ↑ 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.
  7. ↑ 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.
  8. ↑ 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-Phenantrholine and 2,2′-Dipyridyl". Journal of Organometallic Chemistry. 402 (2): 259–263. doi:10.1016/0022-328X(91)83069-G.
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