Borepin

Last updated
Borepin
1H-Borepin.svg
Names
IUPAC name
1H-borepine
Identifiers
3D model (JSmol)
ChemSpider
PubChem CID
  • InChI=1S/C6H7B/c1-2-4-6-7-5-3-1/h1-7H
    Key: LYCCRAPWFYEFFC-UHFFFAOYSA-N
  • B1C=CC=CC=C1
Properties
C6H7B
Molar mass 89.93 g/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Analogues between.jpg

Borepins are a class of boron-containing heterocycles used in main group chemistry. They consist of a seven-membered unsaturated ring with a tricoordinate boron in it. Simple borepins are analogues of cycloheptatriene, which is a seven-membered ring containing three carbon-carbon double bonds, each of which contributes 2π electrons for a total of 6π electrons. Unlike other seven-membered systems such as silepins and phosphepins, boron has a vacant p-orbital that can interact with the π and π* orbitals of the cycloheptatriene. [1] [2] [3] This leads to an isoelectronic state akin to that of the tropylium cation, aromatizing the borepin while also allowing it to act as a Lewis acid. [3] The aromaticity of borepin is relatively weak compared to traditional aromatics such as benzene or even cycloheptatriene, which has led to the synthesis of many fused, π-conjugated borepin systems over the years. [2] [3] [4] [5] [6] [7] Simple and complex borepins have been extensively studied more recently due to their high fluorescence and potential applications in technologies like organic light-emitting diodes (OLEDs) and photovoltaic cells. [3] [5] [7] [8] [9]

Contents

Synthesis

First reported synthetic method

Reaction scheme of o,o'-dibromobibenzyl to make the first reported borepin system. First synthesis.jpg
Reaction scheme of o,o’-dibromobibenzyl to make the first reported borepin system.

The first synthesis of a stable borepin was reported in 1960 by van Tamelen, Brieger, and Untch. The synthesis began with a lithiation of o,o’-dibromobibenzyl. Next it was reacted with tributyl borate to yield a fused borinic acid ring. This product was reacted with n-bromosuccinimide (NBS) to yield a bromo-substituted product. Finally, they performed a dehydrohalogenation to yield the borepin ring system seen above. [10] A method similar to this involving a tin-boron exchange is commonly used in modern synthesis of fused borepin systems. [11]

Synthetic developments

First synthetic procedure for a borepin lacking additional p-conjugation from fused phenyl rings. Heptaphenyl borepin.jpg
First synthetic procedure for a borepin lacking additional π-conjugation from fused phenyl rings.

Eisch and Galle isolated the first non-fused borepin in 1975. The heptaphenyl borabicycloheptadiene on the left went through a suprafacial sigmatropic rearrangement, leading to the intermediate in the middle. This intermediate subsequently underwent disrotatory ring opening to yield heptaphenylborepin on the right. [6] [12] The isolated borepin is kinetically stabilized by the bulky phenyl groups bound to all seven positions on the ring, protecting it from reactions with moisture in the air. However, like most borepins, this compound reacted with oxygen, turning from fluorescent green to purple. [6] [13]

Synthetic route to minimally substituted borepin. Minimal sub.jpg
Synthetic route to minimally substituted borepin.

More recently a method for a minimally substituted borepin was developed by Ashe and Drone. They proceeded from 1,2-dibromocyclopentene and performed a van der Kerk method for boron heterocycle preparation. Next, they initiated a ring closure to form a 7-membered tin complex. Finally, they completed a tin-boron exchange reaction to afford the bicyclic borepin on the right. [2] [14]

Previous synthetic methods yielded heavily substituted and bulky borepin compounds such as heptaphenyl borepin. These routes, while generating very stable complexes, made it difficult to analyze the properties of the borepin ring. Minimal substitution allowed scientists like Ashe to confirm the presence of aromaticity and ring currents within the borepin system. [2] [6] [13] [14]

As more modern methods appeared, the tin-boron exchange reaction has become more commonly used as tin can act as a placeholder in the seven-membered ring, reacting with boryl halides quite easily. [3]

Isomerization

As a final note, in 2018 the Braunschweig group synthesized a valence isomer of borepin, shown below. This bicyclic, boron-containing heterocycle can be interconverted to its borepin isomer using pericyclic, photochemical reactions. [15]

Borepin valence isomer interconversion via photochemical reaction conditions. Borepin valence isomer.jpg
Borepin valence isomer interconversion via photochemical reaction conditions.

Reactivity

While direct functionalization of the boron atom is possible due to its vacant p-orbital, most simple borepins are simply too reactive with air and moisture to be isolated. Therefore, borepins have been stabilized by two general methods: bulky, kinetically stabilizing ligands bound to the boron center and additional aromatic π-systems that can donate electron density into the empty boron p-orbital.

Lewis acid-base adducts

Borepins are of interest due to their Lewis acidity. Density functional theory (DFT) calculations have shown that the HOMO of borepin lies mostly with the carbon moieties of the seven-membered ring, while the LUMO is centered around the boron atom. [3] [5] An example of the HOMO/LUMO distribution can be seen in the figure below.

HOMO/LUMO electronic density mapping. Carbon atoms are in grey while the boron atom is pink/red in the center of the image. Borepin HOMO-LUMO.jpg
HOMO/LUMO electronic density mapping. Carbon atoms are in grey while the boron atom is pink/red in the center of the image.

Chemists like Ashe were able to utilize this knowledge in the 1990s to functionalize borepins as a compound, leading to the formation of many Lewis acid-base adducts. The most common borepin precursor used by chemists is a borepin-halide complex as halides are a good leaving group. [3] [13] The borepin-hydride complex has not been able to be isolated due to its instability, whereas the boron-doped spirocycle on the right side satisfies boron's octet, forming a zwitterion between boron and nitrogen.

Early examples of Lewis acid-base adducts formed from the functionalization of borepins LAB adducts.jpg
Early examples of Lewis acid-base adducts formed from the functionalization of borepins

Borepin cations, anions, and radicals

Using the concept of zwitterions, Gilliard et al. was recently able to synthesize and characterize a cationic borepin state using N-heterocyclic carbenes (NHCs) and cyclic(alkyl)(amino)carbenes (CAACS). Due to the dative donation of NHCs and CAACs, boron has only two covalent bonds, giving it a formal positive charge. [8]

First reported instance of NHC/CAAC stabilized borepinium cations. Antimony hexafluoride (SbF6-) is used as a counterion and does not participate in bonding to the borepin. Boron cation.jpg
First reported instance of NHC/CAAC stabilized borepinium cations. Antimony hexafluoride (SbF6-) is used as a counterion and does not participate in bonding to the borepin.

Most recently, in 2022 Gilliard et al. were able to apply similar principles from their cationic borepins to form and characterize the first instance of isolated borepin radicals. These radicals were also capable of being reduced to the first instance of a borepin anion where there is multiple bonding between a boron-carbon center. [16] The generation of the radical comes from the strong π-accepting ability of the carbene carbon. The electron density shared with the boron center back bonds slightly with the carbon atom, leading to the single-electron radical species.

CAAC stabilized borepin radical. Note the boat conformation the borepin ring adopts to coordinate to the CAAC ligand. Boron radical.jpg
CAAC stabilized borepin radical. Note the boat conformation the borepin ring adopts to coordinate to the CAAC ligand.

Framework manipulation

Spectroscopic data, DFT calculations, and thermochemical data have shown that borepin is weakly aromatic when compared to the tropylium cation. This reduction in aromaticity leads to increased reactivity and instability at the boron center as there is less electron density being donated to boron's p-orbital. [1] [2] [17] [18]

As a result, chemists sought ways to increase the aromatic character of borepins. The tried-and-true method by which chemists stabilize borepins is phenyl-borepin ring fusion (annulation). The addition of two fused phenyl rings increases the 6π borepin system to a 14π fused system.

Most common example of phenyl-borepin fusion. Halide ion is present to showcase borepin before reactions with Lewis bases. Generic borepin on the left explains labeling of atoms for clarity. Bf annulated.jpg
Most common example of phenyl-borepin fusion. Halide ion is present to showcase borepin before reactions with Lewis bases. Generic borepin on the left explains labeling of atoms for clarity.

A complication that arises with fusion of the phenyl rings is their positioning. When synthesizing dibenzo[b,f]borepins (b is the carbon next to the boron atom) they are perfectly aligned for conjugation of the borocycloheptatriene ring. However, if the phenyls are positioned in a [c,e] fashion (see below) then the resulting compound is less stable than dibenzo[b,f]borepins by around 34 kcal/mol, quite a large energy difference. [17]

Example of a dibenzo[c,e]borepin. Note how the phenyls are no longer positioned in conjunction with the borepin p-bonds. Ce borepin.jpg
Example of a dibenzo[c,e]borepin. Note how the phenyls are no longer positioned in conjunction with the borepin π-bonds.

These results explained by Schulman and Disch have been applied many times over to modify borepin frameworks. Some common examples include increasing the number of rings—making boron-doped polycyclic-aromatic hydrocarbons (PAHs), adding additional R groups to the framework such as alkynes and long-chain alkanes, and even introducing electron-rich heteroatoms such as nitrogen or sulfur in order to further stabilize the borepins. [4] [9] [11] [19] [20] Some examples of these compounds can be seen in the image below:

The presence of extremely bulky stabilizing groups on the boron heteroatom keep borepins, especially the fused diborepin, from rapidly decomposing. Other examples.jpg
The presence of extremely bulky stabilizing groups on the boron heteroatom keep borepins, especially the fused diborepin, from rapidly decomposing.

The rapid development of borepin stabilization and functionalization since the 2000s has catapulted studies of complex and versatile molecules. Like many other main group compounds, borepins have been in the field since the mid-late 1900s yet lay dormant until more modern methods could utilize them.

Photophysical properties

Fluorescence/phosphorescence

The first reports of fluorescence in a borepin was published in 1975 by Eisch and Galle and described how heptaphenylborepin was fluorescent green when probed. [6] Little photophysical phenomena were recorded for many years, until Piers's group published the first example of a blue-fluorescent borepin species in 2009. [5] They discovered that by expanding the π-system (i.e. adding more fused phenyl rings) they could dramatically shift the wavelength of their compounds from around 250 nanometers (nm) to upwards of 450 nm. The rationale behind this shift is that the presence of boron in the aromatic system decreases the energy gap between the HOMO and LUMO, resulting in changing absorptions and greater intensity of fluorescence. [5] Similar results were reported by Caruso, Tovar, and Siegler in 2010 when they ran borepins through electrochemical redox reactions and by Messersmith, Siegler, and Tovar in 2016 when testing the effects of variable aromaticity of borepins. [21] [22]

The initial excitement behind these results was the potential for use in electronic materials such as organic light-emitting diodes (OLEDs). If the fluorescence “switch” could be controlled, in addition to having stable borepin complexes, then it would be relatively easy and cheap to achieve bright fluorescent lights, potentially of any color. [20]

Another potential of redox chemistry is the use of boron-containing polycyclic aromatic hydrocarbons as semiconductors. Because of borepins’ low-lying LUMO, it can act as an electron acceptor to participate in electron transport. The Wagner group as well as Toscano and co-workers showed computationally and experimentally the potential applications for these complexes. [4] [23]

On another note, scientists have sought to utilize borepins as potential anion sensors. In the past, tri-coordinate boranes have been used to detect anions like fluoride, cyanide, and even ammonia. [21] [24] [25] Scientists like Adachi and Ohshita have demonstrated that upon coordination of fluoride (F−) fluorescence increases by many magnitudes. [24]

Figure shows fluorescence output of anthracene-substituted tetracyclic borepins upon titration with increasing equivalents of tetrabutylammoniumfluoride (TBAF). Increase of intensity correlates positively between compounds as TBAF is added. High res fluorescence.jpg
Figure shows fluorescence output of anthracene-substituted tetracyclic borepins upon titration with increasing equivalents of tetrabutylammoniumfluoride (TBAF). Increase of intensity correlates positively between compounds as TBAF is added.

In contrast to that example, upon addition of cyanide to one of their borepin analogues to tetrathienoanthracence, Adachi and Ohshita saw a loss of fluorescence. However, upon cooling, there was a noticeable phosphorescence in solution. [25]

Fluorescence is not only limited to outside coordination. Upon insertion of nitrogen into the borepin ring, Li et al. were able to observe solvatochromic effects. Upon addition of the borepin to hexanes, toluene, tetrahydrofuran (THF), dichloromethane (DCM) and acetonitrile (MeCN), rather drastic changes in color were observed. [9]

Solvatochromic property of N-doped diazoborepins. Super high res solv.png
Solvatochromic property of N-doped diazoborepins.

Related Research Articles

<span class="mw-page-title-main">Aromatic compound</span> Compound containing rings with delocalized pi electrons

Aromatic compounds or arenes are organic compounds "with a chemistry typified by benzene" and "cyclically conjugated." The word "aromatic" originates from the past grouping of molecules based on odor, before their general chemical properties were understood. The current definition of aromatic compounds does not have any relation to their odor. Aromatic compounds are now defined as cyclic compounds satisfying Hückel's Rule. Aromatic compounds have the following general properties:

<span class="mw-page-title-main">Aromaticity</span> Chemical property

In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected by the stabilization of conjugation alone. The earliest use of the term was in an article by August Wilhelm Hofmann in 1855. There is no general relationship between aromaticity as a chemical property and the olfactory properties of such compounds.

<span class="mw-page-title-main">Azulene</span> Chemical compound

Azulene is an aromatic organic compound and an isomer of naphthalene. Naphthalene is colourless, whereas azulene is dark blue. The compound is named after its colour, as "azul" is Spanish for blue. Two terpenoids, vetivazulene (4,8-dimethyl-2-isopropylazulene) and guaiazulene (1,4-dimethyl-7-isopropylazulene), that feature the azulene skeleton are found in nature as constituents of pigments in mushrooms, guaiac wood oil, and some marine invertebrates.

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. The dipolarophile is typically an alkene or alkyne, but can be other pi systems. When the dipolarophile is an alkyne, aromatic rings are generally produced.

<span class="mw-page-title-main">Borazine</span> Boron compound

Borazine, also known as borazole, inorganic benzene, is an inorganic compound with the chemical formula B3H6N3. In this cyclic compound, the three BH units and three NH units alternate. The compound is isoelectronic and isostructural with benzene. For this reason borazine is sometimes referred to as “inorganic benzene”. Like benzene, borazine is a colourless liquid with an aromatic odor.

<span class="mw-page-title-main">Corannulene</span> Chemical compound

Corannulene is a polycyclic aromatic hydrocarbon with chemical formula C20H10. The molecule consists of a cyclopentane ring fused with 5 benzene rings, so another name for it is [5]circulene. It is of scientific interest because it is a geodesic polyarene and can be considered a fragment of buckminsterfullerene. Due to this connection and also its bowl shape, corannulene is also known as a buckybowl. Buckybowls are fragments of buckyballs. Corannulene exhibits a bowl-to-bowl inversion with an inversion barrier of 10.2 kcal/mol (42.7 kJ/mol) at −64 °C.

In organic chemistry, a cyclophane is a hydrocarbon consisting of an aromatic unit and a chain that forms a bridge between two non-adjacent positions of the aromatic ring. More complex derivatives with multiple aromatic units and bridges forming cagelike structures are also known. Cyclophanes are well-studied examples of strained organic compounds.

<span class="mw-page-title-main">Cyclic compound</span> Molecule with a ring of bonded atoms

A cyclic compound is a term for a compound in the field of chemistry in which one or more series of atoms in the compound is connected to form a ring. Rings may vary in size from three to many atoms, and include examples where all the atoms are carbon, none of the atoms are carbon, or where both carbon and non-carbon atoms are present. Depending on the ring size, the bond order of the individual links between ring atoms, and their arrangements within the rings, carbocyclic and heterocyclic compounds may be aromatic or non-aromatic; in the latter case, they may vary from being fully saturated to having varying numbers of multiple bonds between the ring atoms. Because of the tremendous diversity allowed, in combination, by the valences of common atoms and their ability to form rings, the number of possible cyclic structures, even of small size numbers in the many billions.

<span class="mw-page-title-main">Homoaromaticity</span> Organic molecular structure

Homoaromaticity, in organic chemistry, refers to a special case of aromaticity in which conjugation is interrupted by a single sp3 hybridized carbon atom. Although this sp3 center disrupts the continuous overlap of p-orbitals, traditionally thought to be a requirement for aromaticity, considerable thermodynamic stability and many of the spectroscopic, magnetic, and chemical properties associated with aromatic compounds are still observed for such compounds. This formal discontinuity is apparently bridged by p-orbital overlap, maintaining a contiguous cycle of π electrons that is responsible for this preserved chemical stability.

<span class="mw-page-title-main">Bis(benzene)chromium</span> Chemical compound

Bis(benzene)chromium is the organometallic compound with the formula Cr(η6-C6H6)2. It is sometimes called dibenzenechromium. The compound played an important role in the development of sandwich compounds in organometallic chemistry and is the prototypical complex containing two arene ligands.

<span class="mw-page-title-main">Borirene</span> Chemical compound

Borirenes are a unique class of three-membered heterocyclic compounds characterized by an unsaturated boron atom within their ring structure. First computationally predicted by John Pople and Paul von Rague Schleyer in 1981, the simplest borirene, (CH)2BH, is isoelectronic with the cyclopropenium cation and exhibits Hückel aromaticity. Borirenes undergo ring-opening reactions with polar reagents and form Lewis adducts, due to the significant ring strain in its three-membered structure and the presence of an empty p orbital on the boron atom. The balance of these two properties leads to unique properties as a ligand for transition metals, in addition to observation of photochemical rearrangement and ring expansion. While borirenes were first discovered in the 1980s, new derivatives such as benzoborirenes have led to renewed interest in the field, with their potential applications yet to be fully explored.

<span class="mw-page-title-main">Boroxine</span> 6-sided cyclic compound of oxygen and boron

Boroxine is a 6-membered heterocyclic compound composed of alternating oxygen and singly-hydrogenated boron atoms. Boroxine derivatives such as trimethylboroxine and triphenylboroxine also make up a broader class of compounds called boroxines. These compounds are solids that are usually in equilibrium with their respective boronic acids at room temperature. Beside being used in theoretical studies, boroxine is primarily used in the production of optics.

Boroles represent a class of molecules known as metalloles, which are heterocyclic 5-membered rings. As such, they can be viewed as structural analogs of cyclopentadiene, pyrrole or furan, with boron replacing a carbon, nitrogen and oxygen atom respectively. They are isoelectronic with the cyclopentadienyl cation C5H+5 or abbreviated as Cp+ and comprise four π electrons. Although Hückel's rule cannot be strictly applied to borole, it is considered to be antiaromatic due to having 4 π electrons. As a result, boroles exhibit unique electronic properties not found in other metalloles.

<span class="mw-page-title-main">Kekulene</span> Chemical compound

Kekulene is a polycyclic aromatic hydrocarbon which consists of 12 fused benzene rings arranged in a circle. It is therefore classified as a [12]-circulene with the chemical formula C48H24. It was first synthesized in 1978, and was named in honor of August Kekulé, the discoverer of the structure of the benzene molecule.

<span class="mw-page-title-main">E. D. Jemmis</span> Indian theoretical chemist

Eluvathingal Devassy Jemmis is a professor of theoretical chemistry at the Indian Institute of Science, Bangalore, India. He was the founding director of Indian Institute of Science Education and Research, Thiruvananthapuram (IISER-TVM). His primary area of research is applied theoretical chemistry with emphasis on structure, bonding and reactivity, across the periodic table of the elements. Apart from many of his contributions to applied theoretical chemistry, an equivalent of the structural chemistry of carbon, as exemplified by the Huckel 4n+2 Rule, benzenoid aromatics and graphite, and tetrahedral carbon and diamond, is brought in the structural chemistry of boron by the Jemmis mno rules which relates polyhedral and macropolyhedral boranes to allotropes of boron and boron-rich solids. He has been awarded Padma Shri in Science and Engineering category by the Government of India.

<span class="mw-page-title-main">Borylene</span>

A borylene is the boron analogue of a carbene. The general structure is R-B: with R an organic moiety and B a boron atom with two unshared electrons. Borylenes are of academic interest in organoboron chemistry. A singlet ground state is predominant with boron having two vacant sp2 orbitals and one doubly occupied one. With just one additional substituent the boron is more electron deficient than the carbon atom in a carbene. For this reason stable borylenes are more uncommon than stable carbenes. Some borylenes such as boron monofluoride (BF) and boron monohydride (BH) the parent compound also known simply as borylene, have been detected in microwave spectroscopy and may exist in stars. Other borylenes exist as reactive intermediates and can only be inferred by chemical trapping.

<span class="mw-page-title-main">9-Borafluorene</span> Class of chemical compounds

9-borafluorenes are a class of boron-containing heterocycles consisting of a tricyclic system with a central BC4 ring with two fused arene groups. 9-borafluorenes can be thought of as a borole with two fused arene rings, or as a trigonal planar boron atom with an empty p orbital bridging two biphenyl rings. However, 9-borafluorenes are generally less reactive than boroles due to less antiaromatic character and Lewis acidity. Containing highly conjugated π systems, 9-borafluorenes possess interesting photophysical properties. In addition, 9-borafluorenes are good Lewis acids. This combination of properties enables potential uses such as in light-emitting materials, solar cells, and sensors for some molecules.

<i>N</i>-Heterocyclic carbene boryl anion Isoelectronic structure

An N-heterocyclic carbene boryl anion is an isoelectronic structure of an N-heterocyclic carbene (NHC), where the carbene carbon is replaced with a boron atom that has a -1 charge. NHC boryl anions have a planar geometry, and the boron atom is considered to be sp2-hybridized. They serve as extremely strong bases, as they are very nucleophilic. They also have a very strong trans influence, due to the σ-donation coming from the boron atom. NHC boryl anions have stronger electron-releasing character when compared to normal NHCs. These characteristics make NHC boryl anions key ligands in many applications, such as polycyclic aromatic hydrocarbons, and more commonly low oxidation state main group element bonding.

<span class="mw-page-title-main">Boraacenes</span> Boron containing acene compounds

Boraacenes are polycyclic aromatic hydrocarbons containing at least one boron atom. Structurally, they are related to acenes, linearly fused benzene rings. However, the boron atom is electron deficient and may act as a Lewis Acid when compared to carbon. This results in slightly less negative charge within the ring, smaller HOMO-LUMO gaps, as well as differences in redox chemistry when compared to their acene analogues. When incorporated into acenes, Boron maintains the planarity and aromaticity of carbon acenes, while adding an empty p-orbital, which can be utilized for the fine tuning of organic semiconductor band gaps. Due to this empty p orbital, however, it is also highly reactive when exposed to nucleophiles like water or normal atmosphere, as it will readily be attacked by oxygen, which must be addressed to maintain its stability.

Diboraanthracene is a class of boron heterocyclic compounds in which two boron atoms substitute two carbon atoms in anthracene (C₁₄H₁₀), one of the typical polycyclic aromatic hydrocarbons (PAHs). The most well-studied diboraanthracene is 9,10-disubstituted-9,10-diboraanthracene (DBA) and its doubly reduced dianion (DBA²⁻). DBA can be readily derivatized and polymerized to afford novel optoelectronic materials with tunable properties. DBA is also a bidentate lewis acid that forms adducts with lewis bases and catalyzes certain Diels-Alder reactions. The dianion DBA²⁻ is formally a mixed-valence, main-group ambiphile with a B(I)/B(III) frustrated lewis pair (FLP)., but the extra electrons are effectively delocalized in the aromatic system. Therefore, DBA²⁻ exhibits both FLP- and transition metal-like reactivities, enabling the activation of a variety of small molecules through distinct pathways and mechanisms

References

  1. 1 2 Schulman, Jerome M.; Disch, Raymond L. (March 1989). "Thermochemistry of borabenzene and borepin". Organometallics. 8 (3): 733–737. doi:10.1021/om00105a024.
  2. 1 2 3 4 5 Ashe, A. J.; Drone, F. J.; Kausch, C. M.; Kroker, J.; Al-Taweel, S. M. (1 January 1990). "Borepins and group 15 element heteroles". Pure and Applied Chemistry. 62 (3): 513–517. doi: 10.1351/pac199062030513 . S2CID   96223530.
  3. 1 2 3 4 5 6 7 Wang, Lili; Ma, Juan; Si, Erbing; Duan, Zheng (February 2021). "Recent Advances in Luminescent Annulated Borepins, Silepins, and Phosphepins". Synthesis. 53 (4): 623–635. doi:10.1055/s-0040-1705946. S2CID   228982156.
  4. 1 2 3 Schickedanz, Kai; Radtke, Julian; Bolte, Michael; Lerner, Hans-Wolfram; Wagner, Matthias (22 February 2017). "Facile Route to Quadruply Annulated Borepins". Journal of the American Chemical Society. 139 (7): 2842–2851. doi: 10.1021/jacs.7b00268 . PMID   28125773.
  5. 1 2 3 4 5 6 Mercier, Lauren G.; Piers, Warren E.; Parvez, Masood (29 July 2009). "Benzo- and Napthoborepins: Blue-Emitting Boron Analogues of Higher Acenes". Angewandte Chemie International Edition. 48 (33): 6108–6111. doi: 10.1002/anie.200902803 . PMID   19598197.
  6. 1 2 3 4 5 Eisch, John J.; Galle, James E. (July 1975). "Rearrangements of organometallic compounds. XIII. Boraaromatic systems. IV. Synthesis of heptaphenylborepin via the thermal rearrangement of heptaphenyl-7-borabicyclo[2.2.1]heptadiene". Journal of the American Chemical Society. 97 (15): 4436–4437. doi:10.1021/ja00848a070.
  7. 1 2 Adachi, Yohei; Ohshita, Joji (26 March 2018). "Synthesis and Properties of Benzo[ d ]dithieno[ b , f ]borepins". Organometallics. 37 (6): 869–881. doi:10.1021/acs.organomet.7b00844.
  8. 1 2 Yang, Wenlong; Krantz, Kelsie E.; Freeman, Lucas A.; Dickie, Diane A.; Molino, Andrew; Kaur, Aishvaryadeep; Wilson, David J. D.; Gilliard, Robert J. (25 September 2019). "Stable Borepinium and Borafluorenium Heterocycles: A Reversible Thermochromic "Switch" Based on Boron–Oxygen Interactions". Chemistry – A European Journal. 25 (54): 12512–12516. doi:10.1002/chem.201903348. PMID   31334883. S2CID   198170504.
  9. 1 2 3 4 Li, Chenglong; Shi, Yafei; Li, Pengfei; Zhang, Niu; Wang, Nan; Yin, Xiaodong; Chen, Pangkuan (17 September 2021). "Access to Highly Luminescent N-Doped Diazaborepins with Penta-, Hexa-, and Heptagon Substructures". Organic Letters. 23 (18): 7123–7128. doi:10.1021/acs.orglett.1c02528. PMID   34449226. S2CID   237339643.
  10. ↑ van Tamelen, E.E.; Brieger, G.; Untch, K.G. (14 March 1960). "Synthesis of a borepin". Tetrahedron Letters. 1 (29): 14–15. doi:10.1016/S0040-4039(01)82703-9.
  11. 1 2 Caruso, Anthony; Tovar, John D. (17 June 2011). "Conjugated " B -Entacenes": Polycyclic Aromatics Containing Two Borepin Rings". Organic Letters. 13 (12): 3106–3109. doi:10.1021/ol2010159. PMID   21604774.
  12. ↑ Eisch, John J.; Galle, James E.; Shafii, Babak; Rheingold, Arnold L. (August 1990). "Bora-aromatic systems. 12. Thermal generation and transformation of the borepin ring system: a paradigm of pericyclic processes". Organometallics. 9 (8): 2342–2349. doi:10.1021/om00158a035.
  13. 1 2 3 Ashe, Arthur J.; Klein, Wolfram; Rousseau, Roger (August 1993). "Evaluation of the aromaticity of borepin: synthesis and properties of 1-substituted borepins". Organometallics. 12 (8): 3225–3231. doi:10.1021/om00032a051.
  14. 1 2 Ashe, Arthur J.; Drone, Frederick J. (March 1987). "1-Methyl-4,5-cyclopentenoborepin: a neutral boron analog of tropylium". Journal of the American Chemical Society. 109 (6): 1879–1880. doi:10.1021/ja00240a058.
  15. ↑ Kelch, Hauke; Kachel, Stephanie; Wahler, Johannes; Celik, Mehmet Ali; Stoy, Andreas; Krummenacher, Ivo; Kramer, Thomas; Radacki, Krzysztof; Braunschweig, Holger (12 October 2018). "Borabicyclo[3.2.0]heptadiene: A Fused Bicyclic Isomer of Borepin". Chemistry – A European Journal. 24 (57): 15387–15391. doi:10.1002/chem.201803509. PMID   30095190. S2CID   51953498.
  16. ↑ Hollister, Kimberly K.; Yang, Wenlong; Mondol, Ranajit; Wentz, Kelsie E.; Molino, Andrew; Kaur, Aishvaryadeep; Dickie, Diane A.; Frenking, Gernot; Pan, Sudip; Wilson, David J. D.; Gilliard, Robert J. (7 June 2022). "Isolation of Stable Borepin Radicals and Anions". Angewandte Chemie International Edition. 61 (23): e202202516. doi:10.1002/anie.202202516. PMC   9324096 . PMID   35289046.
  17. 1 2 Schulman, Jerome M.; Disch, Raymond L. (1 July 2000). "Borepin and Its Analogues: Planar and Nonplanar Compounds". Organometallics. 19 (15): 2932–2936. doi:10.1021/om0002733.
  18. ↑ Subramanian, Govindan; Schleyer, Paul von Ragué; Jiao, Haijun (1 May 1997). "Aromaticity of Annelated Borepins". Organometallics. 16 (11): 2362–2369. doi:10.1021/om970008q.
  19. ↑ Levine, David R.; Siegler, Maxime A.; Tovar, John D. (14 May 2014). "Thiophene-Fused Borepins As Directly Functionalizable Boron-Containing π-Electron Systems". Journal of the American Chemical Society. 136 (19): 7132–7139. doi:10.1021/ja502644e. PMID   24738628.
  20. 1 2 Caruso, Anthony; Tovar, John D. (25 February 2011). "Functionalized Dibenzoborepins as Components of Small Molecule and Polymeric π-Conjugated Electronic Materials". The Journal of Organic Chemistry. 76 (7): 2227–2239. doi:10.1021/jo2001726. PMID   21351778.
  21. 1 2 Caruso, Anthony; Siegler, Maxime A.; Tovar, John D. (7 May 2010). "Synthesis of Functionalizable Boron-Containing π-Electron Materials that Incorporate Formally Aromatic Fused Borepin Rings". Angewandte Chemie International Edition. 49 (25): 4213–4217. doi:10.1002/anie.201000411. PMID   20455227.
  22. ↑ Messersmith, Reid E.; Siegler, Maxime A.; Tovar, John D. (1 July 2016). "Aromaticity Competition in Differentially Fused Borepin-Containing Polycyclic Aromatics". The Journal of Organic Chemistry. 81 (13): 5595–5605. doi:10.1021/acs.joc.6b00927. PMID   27224845.
  23. ↑ De Simone, Bruna Clara; Mazzone, Gloria; Marino, Tiziana; Russo, Nino; Toscano, Marirosa (31 August 2018). "On the Electrochromic Properties of Borepins: A Computational Prediction". ACS Omega. 3 (8): 9556–9563. doi:10.1021/acsomega.8b01288. PMC   6645310 . PMID   31459087.
  24. 1 2 3 Adachi, Yohei; Yamada, Kohei; Ohshita, Joji (5 June 2022). "Synthesis and Optical Properties of Anthryl-substituted Tetracyclic Borepins". Chemistry Letters. 51 (6): 654–657. doi:10.1246/cl.220139. S2CID   248313365.
  25. 1 2 Adachi, Yohei; Arai, Fuka; Yamada, Kohei; Kurihara, Maho; Ohshita, Joji (23 May 2022). "Optical Properties of Boron-Incorporated Analogues of Tetrathienoanthracene". Organometallics. 41 (10): 1225–1231. doi:10.1021/acs.organomet.2c00106. S2CID   248735151.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.