Porphyrins are a group of heterocyclic macrocycle organic compounds, composed of four modified pyrrole subunits interconnected at their α carbon atoms via methine bridges (=CH−). In vertebrates, an essential member of the porphyrin group is heme, which is a component of hemoproteins, whose functions include carrying oxygen in the bloodstream. In plants, an essential porphyrin derivative is chlorophyll, which is involved in light harvesting and electron transfer in photosynthesis.
Alkyne metathesis is an organic reaction that entails the redistribution of alkyne chemical bonds. The reaction requires metal catalysts. Mechanistic studies show that the conversion proceeds via the intermediacy of metal alkylidyne complexes. The reaction is related to olefin metathesis.
A corrole is an aromatic tetrapyrrole. The corrin ring is also present in cobalamin (vitamin B12). The ring consists of nineteen carbon atoms, with four nitrogen atoms in the core of the molecule. In this sense, corrole is very similar to porphyrin.
The Ullmann condensation or Ullmann-type reaction is the copper-promoted conversion of aryl halides to aryl ethers, aryl thioethers, aryl nitriles, and aryl amines. These reactions are examples of cross-coupling reactions.
Macrocycles are often described as molecules and ions containing a ring of twelve or more atoms. Classical examples include the crown ethers, calixarenes, porphyrins, and cyclodextrins. Macrocycles describe a large, mature area of chemistry.
In organic chemistry, an aza-crown ether is an aza analogue of a crown ether. That is, it has a nitrogen atom in place of each oxygen atom around the ring. While the parent crown ethers have the formulae (CH2CH2O)n, the parent aza-crown ethers have the formulae (CH2CH2NH)n, where n = 3, 4, 5, 6. Well-studied aza crowns include triazacyclononane, cyclen, and hexaaza-18-crown-6.
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.
DOTA (also known as tetraxetan) is an organic compound with the formula (CH2CH2NCH2CO2H)4. The molecule consists of a central 12-membered tetraaza (i.e., containing four nitrogen atoms) ring. DOTA is used as a complexing agent, especially for lanthanide ions. Its complexes have medical applications as contrast agents and cancer treatments.
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.
In chemistry, metallacrowns are a macrocyclic compounds that consist of metal ions and solely or predominantly heteroatoms in the ring. Classically, metallacrowns contain an [M–N–O] repeat unit in the macrocycle. First discovered by Vincent L. Pecoraro and Myoung Soo Lah in 1989, metallacrowns are best described as inorganic analogues of crown ethers. To date, over 600 reports of metallacrown research have been published. Metallacrowns with sizes ranging from 12-MC-4 to 60-MC-20 have been synthesized.
Cyclam (1,4,8,11-tetraazacyclotetradecane) is an organic compound with the formula (NHCH2CH2NHCH2CH2CH2)2. Classified as an aza-crown ether, it is a white solid that is soluble in water. As a macrocyclic ligand, it binds strongly to many transition metal cations. The compound was first prepared by the reaction of 1,3-dibromopropane and ethylenediamine.
In coordination chemistry, a transition metal NHC complex is a metal complex containing one or more N-heterocyclic carbene ligands. Such compounds are the subject of much research, in part because of prospective applications in homogeneous catalysis. One such success is the second generation Grubbs catalyst.
In coordination chemistry, a macrocyclic ligand is a macrocyclic ring having at least nine atoms and three or more donor sites that serve as ligands that can bind to a central metal ion. Crown ethers and porphyrins are prominent examples. Macrocyclic ligands exhibit high affinity for metal ions.
In chemistry, tetradentate ligands are ligands that bind four donor atoms to a central atom to form a coordination complex. This number of donor atoms that bind is called denticity and is a method of classifying ligands.
In chemistry, decomplexation refers to the removal of a ligand from a coordination complex. Decomplexation is of particular interest when the ligand has been synthesized within the coordination sphere of the metal, as is often the case in organometallic chemistry.
A lanthanocene is a type of metallocene compound that contains an element from the lanthanide series. The most common lanthanocene complexes contain two cyclopentadienyl anions and an X type ligand, usually hydride or alkyl ligand.
Tris(trimethylsilyl)silane is the organosilicon compound with the formula (Me3Si)3SiH (where Me = CH3). It is a colorless liquid that is classified as a hydrosilane since it contains an Si-H bond. The compound is notable as having a weak Si-H bond, with a bond dissociation energy estimated at 84 kcal/mol. For comparison, the Si-H bond in trimethylsilane is 94 kcal/mol. With such a weak bond, the compound is used as a reagent to deliver hydrogen atoms. The compound has been described as an environmentally benign analogue of tributyltin hydride.
In organic chemistry, thia-crown ethers are organosulfur compounds which are the thia analogues of crown ethers. That is, they have a sulfur atom in place of each oxygen atom around the ring. While the parent crown ethers have the formulae (CH2CH2O)n, the parent thia-crown ethers have the formulae (CH2CH2S)n, where n = 3, 4, 5, 6. They have trivial names "x-ane-Sy", where x and y are the number of atoms in the ring and the number of those atoms that are sulfur, respectively. Thia-crown ethers exhibit affinities for transition metals.
Transition metal porphyrin complexes are a family of coordination complexes of the conjugate base of porphyrins. Iron porphyrin complexes occur widely in Nature, which has stimulated extensive studies on related synthetic complexes. The metal-porphyrin interaction is a strong one such that metalloporphyrins are thermally robust. They are catalysts and exhibit rich optical properties, although these complexes remain mainly of academic interest.
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. Although few have any practical value, these complexes have been influential. 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.
![Structure of [Ni(cyclen)(OH2)2] . Color code: O = red, N = blue, Ni = dark blue, white = H, gray = C. CSD CIF JIKJUI.jpg](http://upload.wikimedia.org/wikipedia/commons/thumb/5/5b/CSD_CIF_JIKJUI.jpg/220px-CSD_CIF_JIKJUI.jpg)