Terpyridine
Encyclopedia
Terpyridine is a heterocyclic compound
derived from pyridine
. This colourless solid is used as a ligand in coordination chemistry.
of 2-acetylpyridine and enaminone, which is prepared by the reaction of 2-acetylpyridine with N,N-dimethylformamide dimethyl acetal
.
Alternatively, the base-catalyzed reaction of 2-acetylpyridine with carbon disulfide
followed by alkylation with methyl iodide gives C5H4NCOCH=C(SMe)2. Condensation of this species with 2-acetylpyridine forms the related 1,5-diketone, which condenses with ammonium acetate
to form a terpyridine. Treatment of this derivative with Raney nickel
remove the thioether
group.
Other methods have been developed for the synthesis of terpy and its substituted derivatives. Substituted terpyridines are also synthesized from palladium
-catalyzed cross-coupling reactions. It can be prepared from bis-triazinyl pyridine.
that binds metals at three meridional sites giving two adjacent 5-membered MN2C2 chelate rings. Terpy forms complexes with most transition metal
ion
as do other polypyridine compounds
, such as 2,2'-bipyridine
and 1,10-phenanthroline. Complexes containing two terpyridine complexes, i.e. [M(terpy)2]n+ are common. They differ structurally from the related [M(bipy)3]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, and fairly intense luminescence
.
Because they are pi-acceptors, terpy and bipyridine
too stabilize metals in lower oxidation states. For instance in acetonitrile
solution, it is possible to generate the [M(terpy)2]+ (M = Ni, Co).
Heterocyclic compound
A heterocyclic compound is a cyclic compound which has atoms of at least two different elements as members of its ring. The counterparts of heterocyclic compounds are homocyclic compounds, the rings of which are made of a single element....
derived from pyridine
Pyridine
Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one C-H group replaced by a nitrogen atom...
. This colourless solid is used as a ligand in coordination chemistry.
Synthesis
Terpyridine was first synthesized by G. Morgan and F. H. Burstall in 1932 by the oxidative coupling of pyridines. This method, however, proceeded in low yields. In 1991, a more efficient synthesis was described that involves the condensationCondensation
Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....
of 2-acetylpyridine and enaminone, which is prepared by the reaction of 2-acetylpyridine with N,N-dimethylformamide dimethyl acetal
Acetal
An acetal is a molecule with two single-bonded oxygen atoms attached to the same carbon atom.Traditional usages distinguish ketals from acetals...
.
Alternatively, the base-catalyzed reaction of 2-acetylpyridine with carbon disulfide
Carbon disulfide
Carbon disulfide is a colorless volatile liquid with the formula CS2. The compound is used frequently as a building block in organic chemistry as well as an industrial and chemical non-polar solvent...
followed by alkylation with methyl iodide 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
Ammonium acetate is a chemical compound with the formula CH3COONH4 . It is a white solid, which can be derived from the reaction of ammonia and acetic acid...
to form a terpyridine. Treatment of this derivative with Raney nickel
Raney nickel
Raney nickel is a solid catalyst composed of fine grains of a nickel-aluminium alloy, used in many industrial processes. It was developed in 1926 by American]] engineer Murray Raney as an alternative catalyst for the hydrogenation of vegetable oils in industrial processes...
remove the thioether
Thioether
A thioether is a functional group in organosulfur chemistry with the connectivity C-S-C as shown on right. Like many other sulfur-containing compounds, volatile thioethers have foul odors. A thioether is similar to an ether except that it contains a sulfur atom in place of the oxygen...
group.
Other methods have been developed for the synthesis of terpy and its substituted derivatives. Substituted terpyridines are also synthesized from palladium
Palladium
Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired...
-catalyzed cross-coupling reactions. It can be prepared from bis-triazinyl pyridine.
Properties
Terpyridine is a tridentate ligandLigand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
that binds metals at three meridional sites giving two adjacent 5-membered MN2C2 chelate rings. Terpy forms complexes with most transition metal
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...
ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
as do other polypyridine compounds
Polypyridine complex
Polypyridine complexes are compounds in which a polypyridine, such as 2,2'-bipyridine, 1,10-phenanthroline, or 2,2';6'2"-terpyridine, coordinates to a metal ion....
, such as 2,2'-bipyridine
2,2'-Bipyridine
2,2'-Bipyridine is a organic compound with the formula . This colorless solid, commonly abbreviated bipy or bpy , is an important isomer of the bipyridine family. It is a bidentate chelating ligand, forming complexes with many transition metals...
and 1,10-phenanthroline. Complexes containing two terpyridine complexes, i.e. [M(terpy)2]n+ are common. They differ structurally from the related [M(bipy)3]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
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
and oxidation, and fairly intense luminescence
Luminescence
Luminescence is emission of light by a substance not resulting from heat; it is thus a form of cold body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions, or stress on a crystal. This distinguishes luminescence from incandescence, which is light emitted by a...
.
Because they are pi-acceptors, terpy and bipyridine
Bipyridine
Bipyridines are a family of chemical compounds with the formula 2, which are formed by the coupling of two pyridine rings. Six isomers of bipyridine exist, but two isomers are prominent: 2,2'-bipyridine is a popular ligand in coordination chemistry and 4,4'-bipyridine is a precursor to the...
too stabilize metals in lower oxidation states. For instance in acetonitrile
Acetonitrile
Acetonitrile is the chemical compound with formula . This colourless liquid is the simplest organic nitrile. It is produced mainly as a byproduct of acrylonitrile manufacture...
solution, it is possible to generate the [M(terpy)2]+ (M = Ni, Co).