Endohedral hydrogen fullerene

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Endohedral hydrogen fullerene (H 2@C 60) is an endohedral fullerene containing molecular hydrogen. This chemical compound has a potential application in molecular electronics and was synthesized in 2005 at Kyoto University by the group of Koichi Komatsu. [1] [2] Ordinarily the payload of endohedral fullerenes are inserted at the time of the synthesis of the fullerene itself or is introduced to the fullerene at very low yields at high temperatures and high pressure. This particular fullerene was synthesised in an unusual way in three steps starting from pristine C60 fullerene: cracking open the carbon framework, insert hydrogen gas and zipping up by organic synthesis methods.

Hydrogen Chemical element with atomic number 1

Hydrogen is a chemical element with symbol H and atomic number 1. With a standard atomic weight of 1.008, hydrogen is the lightest element in the periodic table. Its monatomic form (H) is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass. Non-remnant stars are mainly composed of hydrogen in the plasma state. The most common isotope of hydrogen, termed protium, has one proton and no neutrons.

Carbon Chemical element with atomic number 6

Carbon is a chemical element with symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Three isotopes occur naturally, 12C and 13C being stable, while 14C is a radionuclide, decaying with a half-life of about 5,730 years. Carbon is one of the few elements known since antiquity.

Chemical compound Substance composed of multiple elements

A chemical compound is a chemical substance composed of many identical molecules composed of atoms from more than one element held together by chemical bonds. A chemical element bonded to an identical chemical element is not a chemical compound since only one element, not two different elements, is involved.

Contents

Organic synthesis

Scheme 1 presents an overview of the first step, the creation of a 13 membered ring orifice on the fullerene surface. A 1,2,4-triazine 2 is fitted with two phenyl groups and a pyridine group for reasons of solubility and reacted in 1,2-dichlorobenzene with pristine C60 fullerene 2 in a Diels-Alder reaction at high temperature and for an extended reaction time. In this reaction nitrogen is expulsed and an 8-membered ring is formed (3). This orifice is further extended by reaction with singlet oxygen in carbon tetrachloride which causes one of the ring alkene groups to oxidize to a ketone. The 12-ring is extended to a 13-ring by reaction with elemental sulfur in presence of tetrakis(dimethylamino)ethylene.

Triazine any aromatic, heterocyclic compound having a six-membered aromatic ring with three nitrogen heteroatoms

A triazine is class of nitrogen-containing heterocycles. The parent molecules' molecular formula is C3H3N3. They exist in three isomeric forms, 1,3,5-triazines being common.

Pyridine chemical compound

Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one methine group (=CH−) replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-soluble liquid with a distinctive, unpleasant fish-like smell. Pyridine is colorless, but older or impure samples can appear yellow. The pyridine ring occurs in many important compounds, including agrochemicals, pharmaceuticals, and vitamins. Historically, pyridine was produced from coal tar. Today it is synthesized on the scale of about 20,000 tonnes per year worldwide.

Solubility Capacity of a designated solvent to hold a designated solute in homogeneous solution under specified conditions

Solubility is the property of a solid, liquid or gaseous chemical substance called solute to dissolve in a solid, liquid or gaseous solvent. The solubility of a substance fundamentally depends on the physical and chemical properties of the solute and solvent as well as on temperature, pressure and presence of other chemicals of the solution. The extent of the solubility of a substance in a specific solvent is measured as the saturation concentration, where adding more solute does not increase the concentration of the solution and begins to precipitate the excess amount of solute.

Scheme 1. Endohedral hydrogen fullerene overview Fullerene opening overview.png
Scheme 1. Endohedral hydrogen fullerene overview

The proposed reaction mechanism is depicted in a plat surface rendition in scheme 2. In the first step the triazine reacts with the fullerene in a Diels-Alder reaction. In the second step nitrogen is expulsed from the DA adduct 2 resulting in the formation of a fused aza-cyclohexadiene ring followed by a [4+4]cycloaddition to an intermediate 4 with two cyclopropane rings. This intermediate quickly rearranges in a retro [2+2+2]cycloaddition to the 8 membered ring product 5. In silico calculations show that the electrons in the HOMO reside primarily in the double bonds of the butadiene part of the ring and indeed singlet oxygen reacts at these positions through the dioxetane intermediate 6 with alkene cleavage to diketone 7 (only one isomer shown). Elemental sulfur S8 is inserted into the single bond of the diene group leading to the extension of the ring to 13 atoms (structures 8 and 9 are identical). Tetrakis(dimethylamino)ethylene activates this bond for electrophilic sulfur addition either by one-electron reduction or by complexation.

In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs.

A cycloaddition is a chemical reaction, in which "two or more unsaturated molecules combine with the formation of a cyclic adduct in which there is a net reduction of the bond multiplicity." The resulting reaction is a cyclization reaction. Many but not all cycloadditions are concerted and thus pericyclic. Nonconcerted cycloadditions are not pericyclic. As a class of addition reaction, cycloadditions permit carbon–carbon bond formation without the use of a nucleophile or electrophile.

Cyclopropane is the cycloalkane molecule with the molecular formula C3H6, consisting of three carbon atoms linked to each other to form a ring, with each carbon atom bearing two hydrogen atoms resulting in D3h molecular symmetry. The small size of the ring creates substantial ring strain in the structure.

Scheme 2. Endohedral hydrogen fullerene mechanism Fullerene opening flat perspective.png
Scheme 2. Endohedral hydrogen fullerene mechanism

From X-ray crystallography it is determined that the shape of the orifice in the sulfur compound is roughly a circle. Inserting hydrogen in this compound is an easy step taking place with 100% efficiency. Zipping up the orifice is a reversal of the steps required to open the cage. Care must be taken to keep the reaction conditions below 160 °C on order to prevent hydrogen from escaping. m-CPBA oxidizes the sulfur group to a sulfoxide group which can then be extracted from the ring by a photochemical reaction under visible light in toluene. The two ketone groups are re-coupled in a McMurry reaction with titanium tetrachloride and elemental zinc. The reverse cycloadditions take place at 340 °C in a vacuum splitting of 2-cyanopyridine and diphenylacetylene resulting in the formation of H2@C60 at a 40% chemical yield starting from pristine fullerene.

X-ray crystallography Technique used in studying crystal structure

X-ray crystallography (XRC) is a technique used for determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles and intensities of these diffracted beams, a crystallographer can produce a three-dimensional picture of the density of electrons within the crystal. From this electron density, the mean positions of the atoms in the crystal can be determined, as well as their chemical bonds, their crystallographic disorder, and various other information.

Sulfoxide chemical compound containing the sulfinyl group

A sulfoxide is a chemical compound containing a sulfinyl (SO) functional group attached to two carbon atoms. It is a polar functional group. Sulfoxides are the oxidized derivatives of sulfides. Examples of important sulfoxides are alliin, a precursor to the compound that gives freshly crushed garlic its aroma, and dimethyl sulfoxide (DMSO), a common solvent.

McMurry reaction

The McMurry reaction is an organic reaction in which two ketone or aldehyde groups are coupled to an alkene using a titanium chloride compound such as titanium(III) chloride and a reducing agent. The reaction is named after its co-discoverer, John E. McMurry. The McMurry reaction originally involved the use of a mixture TiCl3 and LiAlH4, which produces the active reagent(s). Related species have been developed involving the combination of TiCl3 or TiCl4 with various other reducing agents, including potassium, zinc, and magnesium. This reaction is related to the Pinacol coupling reaction which also proceeds by reductive coupling of carbonyl compounds.

Properties

H2@C60 is found to be a stable molecule. it survives 10 minutes at 500 °C and shows the same chemical reactivity as empty C60. The electronic properties are also largely unaffected.

The process of hydrogen introduction and release can be facilitated by increasing the size of the orifice. This can be done by replacing sulfur by selenium (sodium thiolate, Se8) exploiting larger C-Se bond length. Filling cracked-open fullerene now takes 8 hours at 190 °C at 760 atmospheres (77 MPa) of hydrogen and release between 150 °C and 180 °C is three times as fast compared to the sulfur analogue. The activation energy for release is lowered by 0.7 kcal/mol to 28.2 kcal/mol (2.9 to 118 kJ/mol). [3]

Selenium Chemical element with atomic number 34

Selenium is a chemical element with symbol Se and atomic number 34. It is a nonmetal with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, and also has similarities to arsenic. It rarely occurs in its elemental state or as pure ore compounds in the Earth's crust. Selenium was discovered in 1817 by Jöns Jacob Berzelius, who noted the similarity of the new element to the previously discovered tellurium.

In molecular geometry, bond length or bond distance is the average distance between nuclei of two bonded atoms in a molecule. It is a transferable property of a bond between atoms of fixed types, relatively independent of the rest of the molecule.

The standard atmosphere is a unit of pressure defined as 101325 Pa. It is sometimes used as a reference or standard pressure.

There is evidence that hydrogen in the fullerene cage is not completely shielded from the outside world as one study found that H2@C60 is more efficient at quenching singlet oxygen than empty C60. [4]

Quenching (fluorescence)

Quenching refers to any process which decreases the fluorescence intensity of a given substance. A variety of processes can result in quenching, such as excited state reactions, energy transfer, complex-formation and collisional quenching. As a consequence, quenching is often heavily dependent on pressure and temperature. Molecular oxygen, iodide ions and acrylamide are common chemical quenchers. The chloride ion is a well known quencher for quinine fluorescence. Quenching poses a problem for non-instant spectroscopic methods, such as laser-induced fluorescence.

Singlet oxygen, systematically named dioxygen(singlet) and dioxidene, is a gaseous inorganic chemical with the formula O=O, which is in a quantum state where all electrons are spin paired. It is kinetically unstable at ambient temperature, however the rate of decay is slow.

Related Research Articles

An aromatic hydrocarbon or arene is a hydrocarbon with sigma bonds and delocalized pi electrons between carbon atoms forming a circle. In contrast, aliphatic hydrocarbons lack this delocalization. The term "aromatic" was assigned before the physical mechanism determining aromaticity was discovered; the term was coined as such simply because many of the compounds have a sweet or pleasant odour. The configuration of six carbon atoms in aromatic compounds is known as a benzene ring, after the simplest possible such hydrocarbon, benzene. Aromatic hydrocarbons can be monocyclic (MAH) or polycyclic (PAH).

A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, commas and plus (+) and minus (−) signs. These are limited to a single typographic line of symbols, which may include subscripts and superscripts. A chemical formula is not a chemical name, and it contains no words. Although a chemical formula may imply certain simple chemical structures, it is not the same as a full chemical structural formula. Chemical formulas can fully specify the structure of only the simplest of molecules and chemical substances, and are generally more limited in power than are chemical names and structural formulas.

Fullerene allotrope of carbon

A fullerene is an allotrope of carbon in the form of a hollow sphere, ellipsoid, tube, and many other shapes and sizes. Spherical fullerenes, also referred to as Buckminsterfullerenes or buckyballs, resemble the balls used in association football. Cylindrical fullerenes are also called carbon nanotubes (buckytubes). Fullerenes are similar in structure to graphite, which is composed of stacked graphene sheets of linked hexagonal rings. Unless they are cylindrical, they must also contain pentagonal rings.

Buckminsterfullerene chemical compound

Buckminsterfullerene is a type of fullerene with the formula C60. It has a cage-like fused-ring structure (truncated icosahedron) that resembles a soccer ball (football), made of twenty hexagons and twelve pentagons, with a carbon atom at each vertex of each polygon and a bond along each polygon edge.

The following outline is provided as an overview of and topical guide to organic chemistry:

Hydrogenolysis is a chemical reaction whereby a carbon–carbon or carbon–heteroatom single bond is cleaved or undergoes lysis (breakdown) by hydrogen. The heteroatom may vary, but it usually is oxygen, nitrogen, or sulfur. A related reaction is hydrogenation, where hydrogen is added to the molecule, without cleaving bonds. Usually hydrogenolysis is conducted catalytically using hydrogen gas.

Tetrahedrane chemical compound

Tetrahedrane is a platonic hydrocarbon with chemical formula C4H4 and a tetrahedral structure. The molecule is subject to considerable angle strain. A number of derivatives have been prepared. Tetrahedranes describe a class of molecules and ions with related structures, e.g. white phosphorus.

The 1,3-dipolar cycloaddition is a chemical reaction between a 1,3-dipole and a dipolarophile to form a five-membered ring. The earliest 1,3-dipolar cycloadditions were described in the late 19th century to the early 20th century, following the discovery of 1,3-dipoles. Mechanistic investigation and synthetic application were established in the 1960s, primarily through the work of Rolf Huisgen. Hence, the reaction is sometimes referred to as the Huisgen cycloaddition. 1,3-dipolar cycloaddition is an important route to the regio- and stereoselective synthesis of five-membered heterocycles and their ring-opened acyclic derivatives.

Thiazole, or 1,3-thiazole, is a heterocyclic compound that contains both sulfur and nitrogen; the term 'thiazole' also refers to a large family of derivatives. Thiazole itself is a pale yellow liquid with a pyridine-like odor and the molecular formula C3H3NS. The thiazole ring is notable as a component of the vitamin thiamine (B1).

Sulfur monoxide chemical compound

Sulfur monoxide is an inorganic compound with formula SO. It is only found as a dilute gas phase. When concentrated or condensed, it converts to S2O2 (disulfur dioxide). It has been detected in space but is rarely encountered intact otherwise.

An alkyne trimerisation reaction is a 2+2+2 cyclization reaction in which three molecules of alkyne react to form an arene. The reaction requires metal catalysts. The process is of historic interest as well as being applicable to organic synthesis. Many variations have been developed including cyclization of mixtures of alkynes and alkenes as well as alkynes and nitriles.

Endohedral fullerene class of chemical compounds

Endohedral fullerenes, also called endofullerenes, are fullerenes that have additional atoms, ions, or clusters enclosed within their inner spheres. The first lanthanum C60 complex was synthesized in 1985 and called La@C60. The @ (at sign) in the name reflects the notion of a small molecule trapped inside a shell. Two types of endohedral complexes exist: endohedral metallofullerenes and non-metal doped fullerenes.

Thioketone

Thioketones (also known as thiones or thiocarbonyls) are organosulfur compounds related to conventional ketones in which the oxygen has been replaced by a sulfur. Instead of a structure of R2C=O, thioketones have the structure R2C=S, which is reflected by the prefix "thio-" in the name of the functional group. Unhindered alkylthioketones typically tend to form polymers or rings.

Prato reaction

The Prato reaction is a particular example of the well-known 1,3-dipolar cycloaddition of azomethine ylides to olefins. In fullerene chemistry this reaction refers to the functionalization of fullerenes and nanotubes. The amino acid sarcosine reacts with paraformaldehyde when heated at reflux in toluene to an ylide which reacts with a double bond in a 6,6 ring position in a fullerene via a 1,3-dipolar cycloaddition to yield a N-methylpyrrolidine derivative or pyrrolidinofullerene or pyrrolidino[[3,4:1,2]] [60]fullerene in 82% yield based on C60 conversion.

Disulfur dichloride chemical compound

Disulfur dichloride is the chemical compound of sulfur and chlorine with the formula S2Cl2.

Fullerene chemistry

Fullerene chemistry is a field of organic chemistry devoted to the chemical properties of fullerenes. Research in this field is driven by the need to functionalize fullerenes and tune their properties. For example, fullerene is notoriously insoluble and adding a suitable group can enhance solubility. By adding a polymerizable group, a fullerene polymer can be obtained. Functionalized fullerenes are divided into two classes: exohedral fullerenes with substituents outside the cage and endohedral fullerenes with trapped molecules inside the cage.

Sulfolene chemical compound

Sulfolene, or butadiene sulfone is a cyclic organic chemical with a sulfone functional group. It is a white, odorless, crystalline, indefinitely storable solid, which dissolves in water and many organic solvents. The occasionally reported pungent smell probably originates from adhering sulfur dioxide. The compound is used as a source of butadiene, but it is a versatile synthetic intermediate.In the laboratory it is used as a solid source of butadiene, into which it decomposes by a reverse cycloaddition.

Kuwajima Taxol total synthesis

The Kuwajima Taxol total synthesis by the group of Isao Kuwajima of the Tokyo Institute of Technology is one of several efforts in taxol total synthesis published in the 1990s. The total synthesis of Taxol is considered a landmark in organic synthesis.

Tris(dimethylamino)methane chemical compound

Tris(dimethylamino)methane (TDAM) is the simplest representative of the tris(dialkylamino)methanes of the general formula (R2N)3CH in which three of the four of methane's hydrogen atoms are replaced by dimethylamino groups (−N(CH3)2). Tris(dimethylamino)methane can be regarded as both an amine and an orthoamide.

Cycloparaphenylene

Cycloparaphenylenes (CPPs) are cylindrical molecules made of para-linked benzene rings in a hoop-like structure. For this reason they are sometimes referred to as carbon nanohoops, especially because they can be viewed as a fragment of an armchair carbon nanotube (CNT). CPPs represent a challenging target to synthetic chemists due to the ring strain incurred from forcing benzene rings out of planarity.

References

  1. ↑ Murata, Y; Murata, M; Komatsu, K (2003). "Synthesis, structure, and properties of novel open-cage fullerenes having heteroatom(s) on the rim of the orifice". Chemistry: A European Journal. 9 (7): 1600–9. doi:10.1002/chem.200390184. PMID   12658659.
  2. ↑ Komatsu, K; Murata, M; Murata, Y (2005). "Encapsulation of molecular hydrogen in fullerene C60 by organic synthesis". Science. 307 (5707): 238–40. Bibcode:2005Sci...307..238K. doi:10.1126/science.1106185. PMID   15653499.
  3. ↑ Chuang, Sc; Murata, Y; Murata, M; Mori, S; Maeda, S; Tanabe, F; Komatsu, K (2007). "Fine tuning of the orifice size of an open-cage fullerene by placing selenium in the rim: insertion/release of molecular hydrogen". Chemical Communications (12): 1278–80. doi:10.1039/b616478a. PMID   17356782.
  4. ↑ López-Gejo, J; Martí, Aa; Ruzzi, M; Jockusch, S; Komatsu, K; Tanabe, F; Murata, Y; Turro, Nj (2007). "Can H2 inside C60 communicate with the outside world?". Journal of the American Chemical Society. 129 (47): 14554–5. doi:10.1021/ja076104s. PMID   17985904.
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