Since 1987, when J.-M. Lehn, C. J. Pedersen, and D. J. Cram were honored with the Nobel prize for their results in selective host-guest chemistry, supramolecular chemistry has become a well-known concept and a major field in today’s research community. This concept has been delineated by Lehn: “Supramolecular chemistry may be defined as ‘chemistry beyond the molecule’, bearing on the organized entities of higher complexity that result from the association of two or more chemical species held together by intermolecular
forces.” Self-recognition and self-assembly processes represent the basic operational components underpinning supramolecular chemistry, in which interactions are mainly non-covalent in nature (e.g., van der Waals, hydrogenbonding, ionic, or coordinative interactions); thus, these interactions are weaker and usually reversible when compared to traditional covalent bonds. Nature presents the ultimate benchmarks for the design of artificial supramolecular processes. Inter- and intramolecular non-covalent interactions are of major importance for most biological processes, such as highly selective catalytic reactions and information storage; different non-covalent interactions are present in proteins, giving them their specific structures. DNA represents one of the most famous natural examples, where self-recognition of the complementary base pairs by hydrogen bonding leads to the self-assembly of the double helix. Starting with the development and design of crown ethers, spherands, and cryptands, modern supramolecular chemistry represents the creation of welldefined structures by self-assembly processes (similar to Nature’s well-known systems).
One of the most important interactions used in supramolecular chemistry is metal-ligand coordination. In this arena, chelate complexes derived from N-heteroaromatic ligands, largely based on 2,2′-bipyridine and 2,2′:6′,2″-terpyridine (Figure 1.1), have become an ever-expanding synthetic and structural frontier.
Bipyridine has been known since 1888 when F. Blau first synthesized a bipyridine-iron complex. One year later, it was again Blau who synthesized and analyzed bipyridine by dry distillation of copper picolinate. Since this parent molecule consists of two identical parts, no directed coupling procedure is required for its construction. Therefore, unsubstituted and symmetrically substituted, in particular 4,4′-functionalized, bipyridines are readily accessible in good yields by simple coupling procedures. Apart from this, bipyridine metal complexes (in particular ruthenium complexes) have very interesting photochemical properties making them ideal candidates for solar energy conversion.
The chemistry of 2,2′:6′,2″-terpyridines (designated as simply terpyridine or tpy; its other structural isomers are duly noted and will not be considered further here) is much younger than that of 2,2′-bipyridines. In the early 1930s, terpyridine was isolated for the first time by Morgan and Burstall , who heated (340 °C) pyridine with anhydrous FeCl3 in an autoclave (50 atm) for 36 h; the parent terpyridine was isolated along with a myriad of other N-containing products. It was subsequently discovered that the addition of Fe(II) ions to a solution of terpyridine compounds gave rise to a purple color giving the first indication of metal complex formation. Since this pioneering work was performed, the chemistry of terpyridine remained merely a curiosity for nearly 60 years, at which point its unique properties were incorporated into the construction of supramolecular assemblies. The number of publications dealing with terpyridine has risen sharply since it is a pivotal structural component in newly engineered constructs based on metallo-polymers and crystal engineering.
The terpyridine molecule contains three nitrogen atoms and can therefore act s a tridentate ligand. It has been extensively studied as an outstanding complexing ligand for a wide range of transition metal ions. The ever-expanding potential applications are the result of advances in the design and synthesis of tailored terpyridine derivatives. The well-known characteristics of terpyridine metal complexes are their special redox and photophysical properties, which greatly depend on the electronic influence of the substituents. Therefore, terpyridine complexes may be used in photochemistry for the design of luminescent devices or as sensitizers for light-to-electricity conversion. Ditopic terpyridinyl units may form polymetallic species that can be used to prepare luminescent or electrochemical sensors. In clinical chemistry and biochemistry, functionalized terpyridines have found a wide range of potential applications, from colorimetric metal determination to DNA binding agents and anti-tumor research.
Terpyridines have also been utilized for catalytic purposes and in asymmetric catalysis. Another interesting application regarding novel supramolecular architectures is the formation of “mixed complexes”, where two differently functionalized terpyridine ligands are coordinated to a single transition metal ion. One of the most promising fields for new terpyridine compounds is their unique application in supramolecular chemistry. In this
context, the formation of supramolecular terpyridine containing dendrimers, can be pointed out. Layer-by-layer self-assembly of extended terpyridine complexes on graphite surfaces forms grid-like supramolecular structures. Self-assembly of terpyridine compounds on gold , CdS or TiO2, as well as surface functionalization with specially functionalized terpyridine ligands, should also be mentioned in this context. Terpyridines, incorporated in macromolecules, enable well-defined supramolecular polymer architectures to be formed, opening up the opportunity of “switching” within physical and chemical properties of materials.
The two basic synthetic approaches to terpyridines are by either central ring assembly or coupling methodologies. Ring assembly is still the most prevalent strategy, but because of their multiplicity and efficiency, modern Pd-catalyzed, cross-coupling procedures have recently become seriously competitive and may surpass the traditional ring-closure processes.
Over the last couple of decades, various new terpyridine ring-assembly strategies have been developed; The most common ring assembly of terpyridines is still the well-known Krȍnke condensation. Shanghai UCHEM Inc. has been producing the following terpyridine derivatives with high efficiency.
2,2':6',2"-Terpyridine CAS: 1148-79-4
2,6-Bis(2-pyridyl)-4(1H)-pyridone CAS: 128143-88-4
4'-Hydroxy-2,2':6',2''-terpyridine CAS: 101003-65-0
4'-Chloro-2,2':6’,2”-Terpyridine CAS: 128143-89-5
4’-Bromo-2,2':6',2''-Terpyridine CAS: 149817-62-9
2,2':6',2"-Terpyridine-4'-carboxylic acid CAS: 148332-36-9
4‘-(4-hydroxyphenyl)-2, 2’:6‘, 2“-terpyridine CAS: 89972-79-2
4-(2, 2':6', 2"-Terpyridin-4'-yl)benzaldehyde CAS: 138253-30-2
4'-(4-methoxycarbonylphenyl)-2,2':6',2''-terpyridine CAS: 897037-23-9
4-[2,2':6',2"-terpyridine]-4'-yl-benzoic acid CAS: 158014-74-5
4'-(4-Bromophenyl)-2,2':6',2"-terpyridine CAS: 89972-76-9
4'-(4-Methoxyphenyl)-2,2':6',2"-terpyridine CAS: 13104-56-8
2,2':6',2"-terpyridine-4,4',4"-tricarboxylic acid CAS:216018-58-5
Trimethyl 2,2':6',2"-terpyridine-4,4',4''-tricarboxylate CAS: 330680-46-1
1,4-Bis(2,2':6',2''-terpyridin-4'-yl)benzene CAS: 146406-75-9
All of the above are available under 1Kg from warehouse. If you are interested in, please contact with UCHEM.
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