Terpyridine (2,2';6',2"-terpyridine, often abbreviated to Terpy or Tpy) is a

heterocyclic compound A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Heterocyclic chemistry is the branch of organic chemistry dealing with the synthesis, properties, and ...

derived from

pyridine Pyridine is a basic heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with a d ...

. It is a white solid that is soluble in most organic solvents. The compound is mainly used as a ligand in

coordination chemistry A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...

Synthesis

Terpyridine was first synthesized by G. Morgan and F. H. Burstall in 1932 by the

oxidative coupling Oxidative coupling in chemistry is a coupling reaction of two molecular entities through an oxidative process. Usually oxidative couplings are catalysed by a transition metal complex like in classical cross-coupling reactions, although the underly ...

of pyridines. This method, however, proceeded in low yields. More efficient syntheses have since been described, mainly starting from 2-acetylpyridine. One method produces an enaminone by the reaction of 2-acetylpyridine with

N,N-dimethylformamide Dimethylformamide is an organic compound with the formula ( CH3)2NC(O)H. Commonly abbreviated as DMF (although this initialism is sometimes used for dimethylfuran, or dimethyl fumarate), this colourless liquid is miscible with water and the majo ...

dimethyl

acetal In organic chemistry, an acetal is a functional group with the connectivity . Here, the R groups can be organic fragments (a carbon atom, with arbitrary other atoms attached to that) or hydrogen, while the R' groups must be organic fragments no ...

. The base-catalyzed reaction of 2-acetylpyridine with

carbon disulfide Carbon disulfide (also spelled as carbon disulphide) is a neurotoxic, colorless, volatile liquid with the formula and structure . The compound is used frequently as a building block in organic chemistry as well as an industrial and chemical non ...

followed by alkylation with

methyl iodide Iodomethane, also called methyl iodide, and commonly abbreviated "MeI", is the chemical compound with the formula CH3I. It is a dense, colorless, volatile liquid. In terms of chemical structure, it is related to methane by replacement of one h ...

gives C₅H₄NCOCH=C(SMe)₂. Condensation of this species with 2-acetylpyridine forms the related 1,5-diketone, which condenses with

ammonium acetate Ammonium acetate, also known as spirit of Mindererus in aqueous solution, is a chemical compound with the formula NH4CH3CO2. It is a white, hygroscopic solid and can be derived from the reaction of ammonia and acetic acid. It is available commerci ...

to form a terpyridine. Treatment of this derivative with Raney nickel removes the

thioether In organic chemistry, an organic sulfide (British English sulphide) or thioether is an organosulfur functional group with the connectivity as shown on right. Like many other sulfur-containing compounds, volatile sulfides have foul odors. A sul ...

group. Other methods have been developed for the synthesis of terpyridine and its substituted derivatives. Substituted terpyridines are also synthesized from

palladium Palladium is a chemical element with the symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1803 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas, which was itself na ...

-catalyzed cross-coupling reactions. It can be prepared from bis-triazinyl pyridine.

Properties

Terpyridine is a tridentate

ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...

that binds metals at three meridional sites giving two adjacent 5-membered MN₂C₂ chelate rings. Terpyridine forms complexes with most

transition metal In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that can ...

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

as do other polypyridine compounds, such as 2,2'-bipyridine and

1,10-phenanthroline 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. Abbreviated ...

. Complexes containing two terpyridine complexes, i.e. (Terpy)₂sup>n+ are common. They differ structurally from the related (Bipy)₃sup>n+ complexes in being achiral. Terpyridine complexes, like other polypyridine complexes, exhibit characteristic optical and electrochemical properties: metal-to-ligand charge transfer (MLCT) in the visible region, reversible reduction and

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...

, and fairly intense

luminescence Luminescence is spontaneous emission of light by a substance not resulting from heat; or "cold light". It is thus a form of cold-body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions or stress on a cryst ...

. Because they are pi-acceptors, terpyridine and

bipyridine Bipyridines also known as bipyridyls, dipyridyls, and dipyridines, are a family of chemical compounds with the formula (C5H4N)2, consisting of two pyridyl (C5H4N) rings. Pyridine is an aromatic nitrogen-containing heterocycle. Bipyridines are of si ...

tend to stabilize metals in lower oxidation states. For instance in

acetonitrile Acetonitrile, often abbreviated MeCN (methyl cyanide), is the chemical compound with the formula and structure . This colourless liquid is the simplest organic nitrile (hydrogen cyanide is a simpler nitrile, but the cyanide anion is not clas ...

solution, it is possible to generate the (Terpy)₂sup>+ (M = Ni, Co).

Related compounds

* bis-triazinyl pyridines are related to terpyridine in their binding to metals. *

quaterpyridine Quaterpyridine refers to a family of pyridine derivatives with the formula (NC5H4-C5H3N)2. These compounds can also be viewed as bipyridine decorated with two pyridyl substituents. Several isomers are known. All are colorless solids. One partic ...

References

{{reflist Chelating agents Pyridines Heterocyclic compounds with 3 rings

Synthesis

Properties

Related compounds

See also

References