RESUMEN
Sulfur-bridged cationic diazulenomethenes were synthesized and exhibited high stability even under basic conditions due to the delocalization of positive charge over the whole π-conjugated skeleton. As a result of the effective delocalization and the absence of orthogonally oriented bulky substituents, the cationic π-conjugated skeletons formed a π-stacked array with short interfacial distances. A derivative with SbF6- as a counter anion formed a charge-segregated assembly in the crystalline state, rather than the generally favored charge-by-charge arrangement of oppositely charged species based on electrostatic interactions. Theoretical calculations suggested that the destabilization caused by electrostatic repulsion between two positively charged π-conjugated skeletons is compensated by the dispersion forces. In addition, the counter anion SbF6- played a role in regulating the molecular alignment through Fâ¯H-C and F-S interactions, which resulted in the charge-segregated alignment of the cationic π-skeletons. This characteristic assembled structure gave rise to a high charge-carrier mobility of 1.7 cm2 V-1 s-1 as determined using flash-photolysis time-resolved microwave conductivity.
RESUMEN
Positively charged phosphorus-containing heterocycles are characteristic core skeletons for functional molecules. While various phosphonium-containing five- or six-membered ring compounds have been reported, seven-membered ring phosphepinium has not yet been fully studied. In this study, dithieno[2,3-b;3,2-f]phosphepinium ions containing electron-donating aminophenyl groups were synthesized. An X-ray crystallographic analysis of the resulting donor-acceptor-donor dyes revealed a bent conformation of the central seven-membered ring. This compound exhibited fluorescence in the near-infrared region with a bathochromic shift of 70 nm compared to phosphepine oxide congener and a large Stokes shift. High fluorescence quantum yields were obtained even in polar solvents due to the suppression of the nonradiative decay process. The theoretical study revealed that the phosphepinium skeleton is highly electron-accepting owing to the orbital interaction between a px orbital of the phosphonium moiety and a π* orbital of the 1,3,5-hexatriene moiety. Owing to the lower-lying px orbital in the phosphonium moiety compared with that of the phosphine oxide and the bent conformation of the seven-membered ring, the phosphepinium ring effectively furnishes a px-π* conjugation. A large structural relaxation with the contribution of a quinoidal resonance structure is suggested in the excited state, which is responsible for the intense emission with a large Stokes shift.
RESUMEN
We here disclose that the incorporation of thiophene rings into a seven-membered 8π azepine in a fused fashion produces a useful antiaromatic core for near-infrared (NIR) dyes. In contrast to dibenzazepine derivatives with bent structures, dithieno-fused derivatives with electron-accepting groups adopt flat conformations in the ground state. The dithieno-fused derivatives exhibited broad absorption spectra that cover the visible region as well as sharp emission bands in the NIR region, which are considerably red-shifted relative to those of the dibenzo-fused congeners. Theoretical study revealed two contradictory effects of the less-aromatic thiophene-fused structure, i.e., the enhancement of the antiaromaticity of the adjacent azepine ring and the relief of the antiaromaticity through the contribution of a quinoidal resonance form. The combination of the dithienoazepine core with cationic electron-accepting groups produced a NIR fluorescent dye with an emission at 878â nm in solution.
RESUMEN
Diazulenylmethyl cations bridged with a germanium and tin moiety were synthesized. In these cations, the nature of these elements has impacts on the chemical stability and photophysical properties. Upon aggregation, these cations exhibit absorption bands in the near-infrared region, which are slightly blue-shifted compared to those of silicon-bridged congeners.
RESUMEN
A kinetically-stabilized nitrogen-doped triangulene cation derivative has been synthesized and isolated as the stable diradical with a triplet ground state that exhibits near-infrared emission. As was the case for a triangulene derivative we previously synthesized, the triplet ground state with a large singlet-triplet energy gap was experimentally confirmed by magnetic measurements. In contrast to the triangulene derivative, the nitrogen-doped triangulene cation derivative is highly stable even in solution under air and exhibits near-infrared absorption and emission because the alternancy symmetry of triangulene is broken by the nitrogen cation. Breaking the alternancy symmetry of triplet alternant hydrocarbon diradicals by a nitrogen cation would therefore be an effective strategy to create stable diradicals possessing magnetic properties similar to the parent hydrocarbons but with different electrochemical and photophysical properties.
RESUMEN
We disclose a series of silicon-bridged diazulenylmethyl cations as stable and one-dimensionally π-extended carbocations. Connecting nonbenzenoid azulenes to a carbocation center at an appropriate position while reinforcing a planar arrangement effectively delocalizes a positive charge over the π-conjugated skeleton. This structural constraint endows the carbocations with not only high chemical stability with the pKR+ value of around 9.5, despite the absence of any electron-donating substituents, but also an intense absorption in the red region due to the effective enhancement of the transition dipole moment. X-ray crystallographic analysis revealed an offset π-stacked arrangement with the outer seven-membered ring overlapping in a face-to-face manner, in which both the steric bulk of the vertically oriented substituents on the silicon atom and the location of the counter anion should play a crucial role. Reflecting this molecular arrangement, the π-extended cations exhibited a red-shifted absorption in the near-infrared (NIR) region in both the solid state and aggregated state in solution, indicative of the formation of J-aggregates. More pronounced redshifts in the absorption band upon the formation of the aggregates were observed by proper choice of the substituents on the silicon bridge and the counter anions, and the aggregates exhibited sharp fluorescence bands with the maximum emission wavelength exceeding 800 nm. These results demonstrate the impact of the nonbenzenoid aromatic stabilization of a carbocation and the efficacy of the present design strategy for the construction of a promising π-extended cationic motif that can form NIR-absorbing and emissive J-aggregates.
RESUMEN
Correction for 'Cyclization of 5-alkynones with chromium alkylidene equivalents generated in situ from gem-dichromiomethanes' by Masahito Murai et al., Chem. Commun., 2020, 56, 9711-9714, DOI: .
RESUMEN
A rare example of cyclization with 5-alkynones, which possess non-polar alkynyl and less electrophilic polar keto carbonyl groups, was demonstrated. The key to promoting carbene/alkyne metathesis followed by alkylidenation with pendant C[double bond, length as m-dash]O double bonds was the Schrock-type nucleophilic reactivity of the generated chromium carbene equivalents from readily available diiodomethanes and CrCl2 by simple heating.
RESUMEN
Treatment of 1,n-enynes with gem-dichromiomethane species prepared in situ from 1,1-diiodomethanes and CrCl2 gave alkenylbicycloalkanes. Alkenylcarbene species, which was generated via [2 + 2] cycloaddition with a triple bond, were intercepted by intramolecular cyclopropanation of a pendant double bond, and alkene metathesis did not proceed. This is a very rare example of transformation of alkynyl C≡C with gem-dimetalloalkanes. Silyl- and borylcarbene equivalents generated from gem-(dichromio)silyl- and borylmethanes promoted the coupling and cyclization of enediynes as well as 1,n-enynes.
RESUMEN
Regioselective difunctionalization of two different C-H bonds in one pot using a three-component coupling reaction is described. The reaction order is important for controlling the reactivity and regioselectivity, and the first silylation promotes the second borylation. The introduced formyl, silyl, and boryl functional groups could be independently converted to other functional groups, and the substitution pattern for the resulting benzenes is difficult to access by conventional methods.
RESUMEN
A (µ-aryloxo)rhenium complex was isolated and confirmed as a key precatalyst for rhenium-catalyzed ortho-alkenylation (C-alkenylation) of unprotected phenols with alkynes. The reaction exclusively provided ortho-alkenylphenols; the formation of para or multiply alkenylated phenols and hydrophenoxylation (O-alkenylation) products was not observed. Several mechanistic experiments excluded a classical Friedel-Crafts-type mechanism, leading to the proposed phenolic hydroxyl group assisted electrophilic alkenylation as the most plausible reaction mechanism. For this purpose, the use of rhenium, a metal between the early and late transition metals in the periodic table, was key for the activation of both the soft carbon-carbon triple bond of the alkyne and the hard oxygen atom of the phenol, at the same time. ortho-Selective alkenylation with allenes also provided the corresponding adducts with a substitution pattern different from that obtained by the addition reaction with alkynes.
RESUMEN
A rhenium complex catalyzed the formation of 2-iodo-1H-indene derivatives through iodine and hydrogen migration of 3-iodopropargyl ethers. The reaction proceeded via generation of 1-iodoalkenylrhenium carbene species by sequential 1,2-iodine and 1,5-hydrogen shifts with readily available precursors under neutral conditions. The reaction mechanism and the reactivity of the generated alkenylcarbene species were also investigated.
RESUMEN
Despite the utility of 9-silafluorenes as functional materials and as building blocks, methods for efficient functionalization of their backbone are rare, probably because of the presence of easily cleavable C-Si bonds. Although controlling the regioselectivity of iridium-catalyzed direct borylation of C-H bonds is difficult, we found that bromination and nitration of 2-methoxy-9-silafluorene under mild conditions occurred predominantly at the electron-rich position. The resulting product having methoxy and bromo groups can be utilized as a building block for the synthesis of unsymmetrically substituted 9-silafluorene-containing π-conjugated molecules.
RESUMEN
An operationally simple and direct rhenium-catalyzed ortho-alkenylation ( C-alkenylation) of unprotected phenols with alkynes was developed. The protocol provided ortho-alkenylphenols exclusively, and formation of para- or multiply alkenylated phenols and hydrophenoxylation ( O-alkenylation) products were not observed. The [3 + 2 + 1] cycloaddition of phenols and two alkynes via ortho-alkenylation was also demonstrated, in which the alkynes functioned as both two- and one-carbon units. These reactions proceeded with readily available starting materials under neutral conditions without additional ligands.
RESUMEN
A stannyl-group-substituted gem-dichromiomethane species, generated in situ from CrCl2, TMEDA, and tributyl(diiodomethyl)stannane, worked as an efficient stannylcarbene equivalent to promote cyclopropanation of alkenes. The reaction provided synthetically useful stannylcyclopropanes directly from commercially available unactivated alkenes without using potentially flammable alkylzinc and diazo compounds. Structural characterization of stannyl- and germyl-group-substituted gem-dichromiomethane complexes and the effect of group 14 elements containing substituents for cyclopropanation are also described.
RESUMEN
The operationally simple palladium-catalyzed double-bond migration without heteroatom-containing coordinating functional groups is described. Addition of TaCl5 as a second catalyst greatly enhanced the migration efficiency to provide ß-alkylstyrenes through migration of up to a five-carbon chain. Both catalysts were commercially available, and the reaction occurred without external ligands under neutral conditions. The reaction proceeded via generation of π-allyl palladium species, which enabled the chemoselective double-bond migration of hydrocarbons in the presence of allylethers. Remote functionalization through double-bond migration was also demonstrated using FeCl3 as a second catalyst.
RESUMEN
Combined use of oxorhenium catalysts with triphenyl phosphite as an oxygen acceptor allowed efficient deoxygenative aromatization of oxabicyclic dienes. The reaction proceeded under neutral conditions and was compatible with various functional groups. Combining this deoxygenation with regioselective bromination and trapping of the generated aryne with furan resulted in benzannulative π-extension at the periphery of the PAHs. This enabled direct use of unfunctionalized PAHs for extension of π-conjugation. Iteration of the transformations increased the number of fused-benzene rings one at a time, which has the potential to alter the properties of PAHs by fine-tuning the degree of π-conjugation, shape, and edge topology.
RESUMEN
An iridium-catalyzed regioselective sequential silylation and borylation of heteroarenes was developed, which represents a rare example of unsymmetrical intermolecular C-H bond difunctionalization through the introduction of two different functionalities during a one-pot transformation. Although the substrate scope for the dehydrogenative silylation of heteroarenes has been limited mainly to electron-rich five-membered rings, the current reaction proceeds with both electron-rich and electron-deficient heteroarenes with the aid of heteroatom-directing C-H bond activation. The regioselectivity of the second borylation was controlled by both steric factors and the electronic effect of the silyl group installed in the first step. In combination with the classic cross-coupling reaction, this method provides rapid access to multisubstituted heteroarenes.
RESUMEN
Azulene-fused polycyclic aromatic hydrocarbons (PAHs) were synthesized from commercially available azulene in four steps. The resulting azulene conjugates exhibited significantly narrow HOMO-LUMO bandgaps with high air stability, confirmed by photophysical study. Introduction of azulene also enabled the unique reversible stimuli-responsiveness even with the weak acid and base, which can potentially control the degree of conjugation and optoelectronic properties by simple acid-base and redox processes.