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1.
Hang Peng Jun-Chao Qi Xian-Jiang Song Ren-Gen Xiong Wei-Qiang Liao 《Chemical science》2022,13(17):4936
Organic single-component ferroelectrics, as an important class of metal-free ferroelectrics, are highly desirable because of their easy processing, mechanical flexibility, and biocompatibility. However, although nearly 50 years have passed since the discovery of photochromism in azobenzene-doped cholesteric liquid crystals, ferroelectricity has never been found in azobenzene-based crystals. Here, we use an amino group to substitute a fluorine atom of 2,2′,4,4′,6,6′-hexafluoroazobenzene, which successfully introduces ferroelectricity into 2-amino-2′,4,4′,6,6′-pentafluoroazobenzene (APFA). APFA shows an extremely high Curie temperature (Tc) of 443 K, which is outstanding among single-component ferroelectrics. It also exhibits an indirect optical band gap of 2.27 eV as well as photoisomerization behavior between the trans-form and the cis-form triggered by pedal motion. To our knowledge, APFA is the first azobenzene-based ferroelectric crystal. This work opens an avenue to design excellent single-component ferroelectrics and will inspire the exploration of azobenzene-based ferroelectrics for promising applications in biofriendly ferroelectric devices.The first azobenzene-based organic single-component ferroelectric 2-amino-2′,4,4′,6,6′-pentafluoroazobenzene was designed, which shows an exceptionally high Curie temperature (Tc) of 443 K. 相似文献
2.
Mirae Ok Ka Young Kim Heekyoung Choi Seonghan Kim Shim Sung Lee Jaeheung Cho Sung Ho Jung Jong Hwa Jung 《Chemical science》2022,13(11):3109
The study of chiral self-sorting is extremely important for understanding biological systems and for developing applications for the biomedical field. In this study, we attempted unprecedented chiral self-sorting supramolecular polymerization accompanying helical inversion with Ag+ in one enantiomeric component. Bola-type terpyridine-based ligands (R-L1 and S-L1) comprising R- or S-alanine analogs were synthesized. First, R-L1 dissolved in DMSO/H2O (1 : 1, v/v) forms right-handed helical fibers (aggregate I) via supramolecular polymerization. However, after the addition of AgNO3 (0.2–1.1 equiv.) to the R-L1 ligand, in particular, it was found that aggregate II with left-handed helicity is generated from the [R-L1(AgNO3)2] complex through the [R-L1Ag]+ complex via the dissociation of aggregate I by a multistep with an off pathway, thus demonstrating interesting self-sorting properties driven by helicity and shape discrimination. In addition, the [R-L1(AgNO3)2] complex, which acted as a building block to generate aggregate III with a spherical structure, existed as a metastable product during the formation of aggregate II in the presence of 1.2–1.5 equiv. of AgNO3. Furthermore, the AFM and CD results of two samples prepared using aggregates I and III with different volume ratios were similar to those obtained upon the addition of AgNO3 to free R-L1. These findings suggest that homochiral self-sorting in a mixture system occurred by the generation of aggregate II composed of the [R-L1Ag]+ complex via the rearrangement of both, aggregates I and III. This is a unique example of helicity- and shape-driven chiral self-sorting supramolecular polymerization induced by Ag+ starting from one enantiomeric component. This research will improve understanding of homochirality in complex biological models and contribute to the development of new chiral materials and catalysts for asymmetric synthesis.Chiral self-sorting supramolecular polymerization of bola-type terpyridine-based ligands (R-L1 and S-L1) comprising R- or S-alanine analogs occurred upon addition of Ag+ in one enantiomeric component. 相似文献
3.
Yong Ai Peng-Fei Li Meng-Juan Yang Yu-Qiu Xu Meng-Zhen Li Ren-Gen Xiong 《Chemical science》2022,13(3):748
Plastic ferroelectrics, featuring large entropy changes in phase transitions, hold great potential application for solid-state refrigeration due to the electrocaloric effect. Although conventional ceramic ferroelectrics (e.g., BaTiO3 and KNbO3) have been widely investigated in the fields of electrocaloric material and catalysis, organic plastic ferroelectrics with a high Curie point (Tc) are rarely reported but are of great importance for the sake of environmental protection. Here, we reported an organic plastic ferroelectric, (−)-camphanic acid, which crystallizes in the P21 space group, chiral polar 2 (C2) point group, at room temperature. It undergoes plastic paraelectric-to-ferroelectric phase transition with the Aizu notation of 23F2 and high Tc of 414 K, showing large entropy gain (ΔSt = 48.2 J K−1 mol−1). More importantly, the rectangular polarization–electric field (P–E) hysteresis loop was recorded on the thin film samples with a large saturated polarization (Ps) of 5.2 μC cm−2. The plastic phase transition is responsible for its multiaxial ferroelectric feature. This work highlights the discovery of organic multiaxial ferroelectrics driven by the motive of combining chirality and plastic phase transition, which will extensively promote the practical application of such unique functional materials.An organic plastic ferroelectric, (−)-Camphanic acid, shows multiaxial ferroelectric feature and large entropy gain during the phase transition. 相似文献
4.
Da‐Wei Fu Ji‐Xing Gao Wen‐Hui He Xue‐Qin Huang Yu‐Hua Liu Yong Ai 《Angewandte Chemie (International ed. in English)》2020,59(40):17477-17481
1,4‐Diazabicyclo[2.2.2]octane (dabco) and its derivatives have been extensively utilized as building units of excellent molecular ferroelectrics for decades. However, the homochiral dabco‐based ferroelectric remains a blank. Herein, by adding a methyl (Me) group accompanied by the introduction of homochirality to the [H2dabco]2+ in the non‐ferroelectric [H2dabco][TFSA]2 (TFSA=bis(trifluoromethylsulfonyl)ammonium), we successfully designed enantiomeric ferroelectrics [R and S‐2‐Me‐H2dabco][TFSA]2. The two enantiomers show two sequential phase transitions with transition temperature (Tc) as high as 405.8 K and 415.8 K, which is outstanding in both dabco‐based ferroelectrics and homochiral ferroelectrics. To our knowledge, [R and S‐2‐Me‐H2dabco][TFSA]2 are the first examples of dabco‐based homochiral ferroelectrics. This finding opens an avenue to construct dabco‐based homochiral ferroelectrics and will inspire the exploration of more eminent enantiomeric molecular ferroelectrics. 相似文献
5.
Prof. Da-Wei Fu Dr. Ji-Xing Gao Wen-Hui He Xue-Qin Huang Yu-Hua Liu Prof. Yong Ai 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(40):17630-17634
1,4-Diazabicyclo[2.2.2]octane (dabco) and its derivatives have been extensively utilized as building units of excellent molecular ferroelectrics for decades. However, the homochiral dabco-based ferroelectric remains a blank. Herein, by adding a methyl (Me) group accompanied by the introduction of homochirality to the [H2dabco]2+ in the non-ferroelectric [H2dabco][TFSA]2 (TFSA=bis(trifluoromethylsulfonyl)ammonium), we successfully designed enantiomeric ferroelectrics [R and S-2-Me-H2dabco][TFSA]2. The two enantiomers show two sequential phase transitions with transition temperature (Tc) as high as 405.8 K and 415.8 K, which is outstanding in both dabco-based ferroelectrics and homochiral ferroelectrics. To our knowledge, [R and S-2-Me-H2dabco][TFSA]2 are the first examples of dabco-based homochiral ferroelectrics. This finding opens an avenue to construct dabco-based homochiral ferroelectrics and will inspire the exploration of more eminent enantiomeric molecular ferroelectrics. 相似文献
6.
Martin L. Kirk David A. Shultz Patrick Hewitt Daniel E. Stasiw Ju Chen Art van der Est 《Chemical science》2021,12(41):13704
A change in the sign of the ground-state electron spin polarization (ESP) is reported in complexes where an organic radical (nitronylnitroxide, NN) is covalently attached to a donor–acceptor chromophore via two different meta-phenylene bridges in (bpy)Pt(CAT-m-Ph-NN) (mPh-Pt) and (bpy)Pt(CAT-6-Me-m-Ph-NN) (6-Me-mPh-Pt) (bpy = 5,5′-di-tert-butyl-2,2′-bipyridine, CAT = 3-tert-butylcatecholate, m-Ph = meta-phenylene). These molecules represent a new class of chromophores that can be photoexcited with visible light to produce an initial exchange-coupled, 3-spin (bpy˙−, CAT+˙ = semiquinone (SQ), and NN), charge-separated doublet 2S1 (S = chromophore excited spin singlet configuration) excited state. Following excitation, the 2S1 state rapidly decays to the ground state by magnetic exchange-mediated enhanced internal conversion via the 2T1 (T = chromophore excited spin triplet configuration) state. This process generates emissive ground state ESP in 6-Me-mPh-Pt while for mPh-Pt the ESP is absorptive. It is proposed that the emissive polarization in 6-Me-mPh-Pt results from zero-field splitting induced transitions between the chromophoric 2T1 and 4T1 states, whereas predominant spin–orbit induced transitions between 2T1 and low-energy NN-based states give rise to the absorptive polarization observed for mPh-Pt. The difference in the sign of the ESP for these molecules is consistent with a smaller excited state 2T1 – 4T1 gap for 6-Me-mPh-Pt that derives from steric interactions with the 6-methyl group. These steric interactions reduce the excited state pairwise SQ-NN exchange coupling compared to that in mPh-Pt.A change in the sign of the ground state electron spin polarization (ESP) is reported in complexes where an organic radical (nitronylnitroxide, NN) is covalently attached to a donor–acceptor chromophore via two different meta-phenylene bridges. 相似文献
7.
The self-assembly of palladium-based cages is frequently rationalized via the cumulative enthalpy (ΔH) of bonds between coordination nodes (M, i.e., Pd) and ligand (L) components. This focus on enthalpic rationale limits the complete understanding of the Gibbs free energy (ΔG) for self-assembly, as entropic (ΔS) contributions are overlooked. Here, we present a study of the M2linL3 intermediate species (M = dinitrato(N,N,N′,N′-tetramethylethylenediamine)palladium(ii), linL = 4,4′-bipyridine), formed during the synthesis of triangle-shaped (M3linL3) and square-shaped (M4linL4) coordination macrocycles. Thermochemical analyses by variable temperature (VT) 1H-NMR revealed that the M2linL3 intermediate exhibited an unfavorable (relative) ΔS compared to M3linL3 (triangle, ΔTΔS = +5.22 kcal mol−1) or M4linL4 (square, ΔTΔS = +2.37 kcal mol−1) macrocycles. Further analysis of these constructs with molecular dynamics (MD) identified that the self-assembly process is driven by ΔG losses facilitated by increases in solvation entropy (ΔSsolv, i.e., depletion of solvent accessible surface area) that drives the self-assembly from “open” intermediates toward “closed” macrocyclic products. Expansion of our computational approach to the analysis of self-assembly in PdnbenL2n cages (benL = 4,4''-(5-ethoxy-1,3-phenylene)dipyridine), demonstrated that ΔSsolv contributions drive the self-assembly of both thermodynamic cage products (i.e., Pd12benL24) and kinetically-trapped intermediates (i.e., Pd8cL16).These studies demonstrate that ΔS drives the self-assembly of supramolecular palladium-based coordination macrocycles and cages. As this ΔS contribution arises from solvation, these findings broadly reflect the thermodynamic drive of self-assembly to form compact structures. 相似文献
8.
Chao Liu Yucheng Jin Dongdong Qi Xu Ding Huimin Ren Hailong Wang Jianzhuang Jiang 《Chemical science》2022,13(23):7014
Chiral recognition and discrimination is not only of significance in biological processes but also a powerful method to fabricate functional supramolecular materials. Herein, a pair of heterochiral porous organic cages (HPOC-1), out of four possible enantiomeric products, with mirror stereoisomeric crystal structures were cleanly prepared by condensation occurring in the exclusive combination of cyclohexanediamine and binaphthol-based tetraaldehyde enantiomers. Nuclear magnetic resonance and luminescence spectroscopy have been employed to monitor the assembly process of HPOC-1, revealing the clean formation of heterochiral organic cages due to the enantioselective recognition of (S,S)-binaphthol towards (R,R)-cyclohexanediamine derivatives and vice versa. Interestingly, HPOC-1 exhibits circularly polarized luminescence and enantioselective recognition of chiral substrates according to the circular dichroism spectral change. Theoretical simulations have been carried out, rationalizing both the enantioselective assembly and recognition of HPOC-1.Heterochiral organic cages based on enantioselective self-assembly of binary chiral components have been prepared, exhibiting circularly polarized luminescence property and enantioselective recognition ability towards chiral substrates according to the circular dichroism spectral change. 相似文献
9.
The most fundamental tasks in asymmetric synthesis are the development of fully stereodivergent strategies to access the full complement of stereoisomers of products bearing multiple stereocenters. Although great progress has been made in the past few decades, developing general and practical strategies that allow selective generation of any diastereomer of a reaction product bearing multiple stereocentres through switching distinct chiral catalysts is a significant challenge. Here, attaining precise switching of the product stereochemistry, we develop a novel P-chirogenic ligand, i.e.YuePhos, which can be easily derived from inexpensive and commercially available starting materials in four chemical operations. Through switching of three chiral ligands, an unprecedented ligand-dependent diastereodivergent Pd-catalyzed asymmetric intermolecular [4 + 2] cycloaddition reaction of vinyl benzoxazinanone with α-arylidene succinimides was developed. This novel method provides an efficient route for the stereodivergent synthesis of six stereoisomers of pyrrolidines bearing up to three adjacent stereocenters (one quaternary center). Despite the anticipated challenges associated with controlling stereoselectivity in such a complex system, the products are obtained in enantiomeric excesses ranging up to 98% ee. In addition, the synthetic utilities of optically active hexahydrocarbazoles are also shown.An unprecedented ligand-dependent stereodivergent Pd-catalyzed asymmetric intermolecular [4 + 2] cycloaddition reaction of vinyl benzoxazinanone with α-aryliene succinimides was developed.The chirality of a biologically active molecule can alter its physiological properties. Therefore, highly efficient access to and fully characterizing all possible stereoisomers of a chiral molecule is one of the fundamental challenges in organic synthesis, drug discovery and development processes. However, most asymmetric catalytic transformations afford products enantioselectively and diastereoselectively and only form one of the stereoisomers containing multiple stereocenters. Stereodivergent access to all possible stereoisomers of the products is incredibly difficult because diastereochemical preference is largely dominated by the inherent structural and stereoelectronic characteristics of substrates, while absolute conformation can be dictated by the choice of the chiral catalyst.1 In 2013, Carreira and co-workers addressed this limitation by introducing the concept of stereodivergent dual-catalytic synthesis, reporting the allylation of aldehydes in a diastereodivergent fashion by the synergistic reactivity of iridium and amine catalysts under acidic conditions.2 Soon after, Carreira,3 Zhang,4 Hartwig,5 Dong,6 Wang,7 Zi,8 Lee,9 and other groups10 reported using an appropriate combination of dual chiral catalysts in a series of elegant studies (Scheme 1A). Recently, chemists found, in some cases, that tuning non-chiral parameters, including solvents or additives, also controlled the stereochemical outcomes through subtle perturbation of the key diastereomeric transition states.11 In 2018, You and co-workers reported a solvent-controlled palladium-catalyzed enantioselective dearomative formal [3 + 2] cycloaddition, affording stereodivergent synthesis of two diastereomeric tetrahydrofuroindoles.12 However, a rapid and predictable way to access complete stereoisomers of products bearing multiple stereocentres (for example, three contiguous stereocentres) remains an unsolved challenge through switching of ligands. To the best of our knowledge, only two successful examples were reported by Buchwald and Zhang, in which eight stereoisomers were obtained through tuning catalysts and reactive substrates (Scheme 1B).4a,13Open in a separate windowScheme 1Strategy for stereodivergent synthesis of different stereoisomers.In metal-catalyzed reactions, ligands can manipulate the reactivity and selectivity by affecting the steric and electronic properties of metal catalysts. Therefore, the design and development of new ligands to improve the utility, activity and selectivity of their related metal catalysts are greatly desired by organic chemists. Recently, our groups have synthesized a new and promising class of P-chiral ligands ZD-Phos (including Ganphos and Jiaphos), and their conformational rigidity and chemical robustness have endowed the structure and its variants with outstanding activity and selectivity as well as excellent stereocontrol features essential to asymmetric cycloaddition reactions.14 Inspired by these advances, we are interested in continuing the development of P-chiral ligands with new structural motifs in the search for new reactivity and selectivity to tackle current synthetic challenges. More recently, Sadphos has emerged as another superior chiral skeleton, owing to the pioneering contributions by Zhang.15 Thus its aminophosphine scaffold is envisaged to be introduced into our 1-phosphanorbornene framework (ZD-Phos).16 We aim to combine the advantages of the aforementioned two types of chiral motifs, thus developing a novel P,P-bidentate ligand. Thus the novel P-chiral ligands, called Yuephos, may show unique stereoselectivity in a metal-catalyzed asymmetric cycloaddition reaction (Fig. 1).Open in a separate windowFig. 1Design of the Yuephos framework.Tetrahydroquinolines are important molecular skeletons that widely occur in natural molecules, pharmaceuticals, and functional materials. For this reason, realizing stereodivergent synthesis of all stereoisomers of fully substituted tetrahydroquinolines has been an important and challenging task in organic synthesis. However, to date, full control of absolute and relative stereochemical configuration of these molecules has remained an unmet synthetic challenge. Considering the potentiality of fully substituted chiral tetrahydroquinolines in drug discovery and stereodivergent synthesis,17 we envisioned that using our new palladium/ZD-Phos catalytic system may offer an efficient strategy for overcoming the challenges related to regio-, enantio-, and diastereo-selectivity. Herein, we report our studies on the unexplored stereodivergent synthesis of fully substituted tetrahydroquinolines through ligand-controlled, metal-catalyzed asymmetric annulation. Six possible stereoisomers bearing two tertiary and one quaternary stereocenters were easily synthesized in good yields with high enantio- and diastereo-selectivities from the same starting materials (Scheme 1C).The new bisphosphorus ligands we report herein can be easily synthesized by a two-pot method with good yields (Scheme 2). Starting from the corresponding aldehyde18 and commercially available chiral amine, one-pot sequential reaction gave diastereomers Y1 and Y1′ with 1 : 1 dr, which could be straightforwardly separated by column chromatography. The subsequent reduction using Raney Ni produced the final Yuephos in good yields. The absolute configuration of Yue-1′ was established by single crystal X-ray diffraction.19 Importantly, the ligands Yuephos can remain stable in air and moisture for more than one year.Open in a separate windowScheme 2Synthesis of Yuephos ligands.With new Yuephos ligands in hand, we began our study by choosing vinyl benzoxazinanone 1a with α-phenylidene succinimide 2a as the model substrate, combined with the Pd2dba3·CHCl3/L complex as the catalyst. Details of [Pd] source and solvent screening can be found in the ESI (Table S1 and S2†). Notably, using Pd2dba3·CHCl3/Yuephos as the catalyst in ethyl acetate, the reaction proceeded smoothly, affording the desired product 3a in 69% yield with 96% ee and >20 : 1 dr (entry 1). It should be noted that Yuephos ligands were found to be efficient for this reaction, and the product 3a was obtained in good enantioselectivity with seemingly irregular yields and diastereoselectivities (entries 2–6). Trost''s ligand (L1) and chiral diphosphine ligand (L2) promoted the reaction with good diastereoselectivity but in a low yield and poor enantioselectivity (entries 7–8). However, (R)-SegPhos (L3) failed to afford the desired product (entry 9). To our surprise, when the phosphoramidite ligand (L4) was used, the diastereoselectivity was reversed compared to that in Yuephos (entry 10). Thus, a diastereodivergent phenomenon induced by the chiral ligand was discovered. To further improve the yield and selectivity, various solvents and [Pd] sources were screened (Table S3 and S4 in the ESI†), and an obvious improvement in the enantioselectivity and diastereoselectivity was observed when using DCM as the solvent (entries 10 vs. 11). The reaction enantioselectivity was further increased to 92% with good yield (85%) when the reaction temperature was reduced to −20 °C (entries 12–14).With the optimal conditions established for (S, R, S)-3a (20Optimization of reaction conditionsa
Open in a separate windowaUnless otherwise stated, reactions were performed with 1a (60 mg, 0.2 mmol) and 2a (26 mg, 0.1 mmol), in 1.0 mL of solvent at 15 °C for 72 h, and EA = ethyl acetate; DCM = dichloromethane.bIsolated yield after chromatography.cThe diastereomeric ratios were determined by column chromatography.dDetermined by HPLC analysis.eL4 (10 mol%) was used, Cs2CO3 (2.0 equiv.).fReaction temperature: 0 °C.gReaction temperature: −10 °C.hReaction temperature: −20 °C.Scope of the substrates for the synthesis of (S, R, S)-3a
Open in a separate windowaReaction conditions: see 21Scope of the substrates for the synthesis of (S, S, S)-4aa
Open in a separate windowaReaction conditions: see †). When the Pd/Meng-2 complex was used as the catalyst, its enantiomer (S, S, R)-5 was produced with moderate stereoselectivity (Scheme 3). Fortunately, six stereoisomers could be easily obtained after column chromatography, as confirmed by the high-performance liquid-chromatography traces. To the best of our knowledge, this is the first example of stereodivergent construction of six chiral tetrahydroquinolines containing three contiguous stereocenters by only switching chiral ligands (Scheme 3).Open in a separate windowScheme 3Synthesis of six stereoisomers by switching the chiral ligands. aAfter recrystallization, the mother liquor was tested to get the relevant data.To demonstrate the practicality of the reaction, a scale-up experiment was performed (Scheme 4). To our delight, the products (S, R, S)-3a and (S, S, S)-4a were obtained in 94% ee and 92% ee, respectively. Then, different transformations with regard to tetrahydroquinolines (S, R, S)-3a were conducted. At first, the hydrogenation of (S, R, S)-3a was conducted in the presence of Pd/C, furnishing the desired product 6 in 96% yield. In addition, the product (S, R, S)-3a could undergo selective hydroboration to give the anti-Markovnikov product 7 in 83% yield.Open in a separate windowScheme 4Scale-up experiment transformations of the multifunctional products. 相似文献
Entry | Ligands | Solvent | Yieldb (%) | drc (3a : 4a) | eed (%) |
---|---|---|---|---|---|
1 | Yue-1 | EA | 69 | >20 : 1 | 96 (S, R, S) |
2 | Yue-1′ | EA | 64 | 4 : 1 | 33 (S, R, S) |
3 | Yue-2 | EA | 73 | >20 : 1 | 95 (R, S, R) |
4 | Yue-3 | EA | 60 | 6 : 1 | 80 (S, R, S) |
5 | Yue-4 | EA | 44 | 3 : 1 | 85 (S, R, S) |
6 | Yue-5 | EA | 62 | 14 : 1 | 90 (S, R, S) |
7 | L1 | EA | 31 | >20 : 1 | 14 (S, R, S) |
8 | L2 | EA | 42 | >20 : 1 | 73 (S, R, S) |
9 | L3 | EA | — | — | — |
10e | L4 | EA | 64 | 1 : 15 | 77 (S, S, S) |
11e | L4 | DCM | 89 | <1 : 20 | 87 (S, S, S) |
12e,f | L4 | DCM | 89 | <1 : 20 | 86 (S, S, S) |
13e,g | L4 | DCM | 87 | <1 : 20 | 88 (S, S, S) |
14e,h | L4 | DCM | 85 | <1 : 20 | 92 (S, S, S) |
10.
Cathay Chai Au-Yeung Lok-Kwan Li Man-Chung Tang Shiu-Lun Lai Wai-Lung Cheung Maggie Ng Mei-Yee Chan Vivian Wing-Wah Yam 《Chemical science》2021,12(27):9516
Here, we report the design and synthesis of a new class of fused heterocyclic alkynyl ligand-containing gold(iii) complexes, which show tunable emission colors spanning from the yellow to red region in the solid state and exhibit thermally activated delayed fluorescence (TADF) properties. These complexes display high photoluminescence quantum yields of up to 0.87 and short excited-state lifetimes in sub-microsecond timescales, yielding high radiative decay rate constants on the order of up to 106 s−1. The observation of the drastic enhancement in the emission intensity of the complexes with insignificant change in the excited-state lifetime upon increasing the temperature from 200 to 360 K indicates an increasing radiative decay rate. The experimentally estimated energy splitting between the lowest-lying singlet excited state (S1) and the lowest-lying triplet excited state (T1), ΔES1–T1, is found to be as small as ∼0.03 eV (250 cm−1), comparable to the value of ∼0.05 eV (435 cm−1) obtained from computational studies. The delicate choice of the cyclometalating ligand and the fused heterocyclic ligand is deemed the key to induce TADF through the control of the energy levels of the intraligand and the ligand-to-ligand charge transfer excited states. This work represents the realization of highly emissive yellow- to red-emitting gold(iii) TADF complexes incorporated with fused heterocyclic alkynyl ligands and their applications in organic light-emitting devices.We report the design of a new class of fused heterocyclic alkynyl ligand-containing gold(iii) complexes, which shows tunable emission colors spanning yellow to red region and exhibits thermally activated delayed fluorescence (TADF) properties. 相似文献
11.
The development of chiral crystalline porous materials (CPMs) containing multiple chiral building blocks plays an important role in chiral chemistry and applications but is a challenging task. Herein, we report the first example of bichiral building block based enantiopure CPM films containing metal–organic cages (MOCs) and metal complexes. The functionalized substrate was immersed subsequently into homochiral metal complex (R)- or (S)-Mn(DCH)3 (DCH = 1,2-diaminocyclohexane) and racemic Ti4L6 cage (L = embonate) solutions by a layer-by-layer growth method. During the assembly process, the substrate surface coordinated with (R)- or (S)-Mn(DCH)3 can, respectively, layer-by-layer chiroselectively connect Δ- or Λ-Ti4L6 cages to form homochiral (R, Δ)- or (S, Λ)-CPM films with a preferred [111] growth orientation, tunable thickness and homogeneous surface. The resulting enantiopure CPM films show strong chirality, photoluminescence, and circularly polarized luminescence (CPL) properties as well as good enantioselective adsorption toward enantiomers of 2-butanol and methyl-lactate. The present in situ surface chiroselective strategy opens a new route to assemble homochiral CPM films containing multiple chiral building blocks for chiral applications.Bichiral building block based enantiopure CPM films containing metal–organic cages (MOCs) and metal complexes are chiroselectively assembled on the substrate surface by a layer-by-layer method. 相似文献
12.
Hui Ye Xiao-Xian Chen De-Xuan Liu Bing-Qing Zhao Yao-Bin Li Ying Zeng Wei-Xiong Zhang Xiao-Ming Chen 《Chemical science》2022,13(47):14124
Molecular-based ferroic phase-transition materials have attracted increasing attention in the past decades due to their promising potential as sensors, switches, and memory. One of the long-term challenges in the development of molecular-based ferroic materials is determining how to promote the ferroic phase-transition temperature (Tc). Herein, we present two new hexagonal molecular perovskites, (nortropinonium)[CdCl3] (1) and (nortropinium)[CdCl3] (2), to demonstrate a simple design principle for obtaining ultrahigh-Tc ferroelastic phase transitions. They consist of same host inorganic chains but subtly different guest organic cations featuring a rigid carbonyl and a flexible hydroxyl group in 1 and 2, respectively. With stronger hydrogen bonds involving the carbonyl but a relatively lower decomposition temperature (Td, 480 K), 1 does not exhibit a crystalline phase transition before its decomposition. The hydroxyl group subtly changes the balance of intermolecular interactions in 2via reducing the attractive hydrogen bonds but increasing the repulsive interactions between adjacent organic cations, which finally endows 2 with an enhanced thermal stability (Td = 570 K) and three structural phase transitions, including two ferroelastic phase transitions at ultrahigh Tc values of 463 K and 495 K, respectively. This finding provides important clues to judiciously tuning the intermolecular interactions in hybrid crystals for developing high-Tc ferroic materials.Two new hexagonal molecular perovskites with the same inorganic chain but subtly different organic cations exhibit distinct phase-transition behaviours owing to the different intermolecular interactions. 相似文献
13.
Xinkun Ren Ajay L. Chandgude Daniela M. Carminati Zhuofan Shen Sagar D. Khare Rudi Fasan 《Chemical science》2022,13(29):8550
Organophosphonate compounds have represented a rich source of biologically active compounds, including enzyme inhibitors, antibiotics, and antimalarial agents. Here, we report the development of a highly stereoselective strategy for olefin cyclopropanation in the presence of a phosphonyl diazo reagent as carbene precursor. In combination with a ‘substrate walking’ protein engineering strategy, two sets of efficient and enantiodivergent myoglobin-based biocatalysts were developed for the synthesis of both (1R,2S) and (1S,2R) enantiomeric forms of the desired cyclopropylphosphonate ester products. This methodology enables the efficient transformation of a broad range of vinylarene substrates at a preparative scale (i.e. gram scale) with up to 99% de and ee. Mechanistic studies provide insights into factors that contribute to make this reaction inherently more challenging than hemoprotein-catalyzed olefin cyclopropanation with ethyl diazoacetate investigated previously. This work expands the range of synthetically useful, enzyme-catalyzed transformations and paves the way to the development of metalloprotein catalysts for abiological carbene transfer reactions involving non-canonical carbene donor reagents.Two enantiocomplementary myoglobin-based carbene transfer biocatalysts were developed for the synthesis of cyclopropylphosphonate esters with high diastereo- and enantioselectivity and in high yields. 相似文献
14.
M. Jeremy Amdur Kathleen R. Mullin Michael J. Waters Danilo Puggioni Michael K. Wojnar Mingqiang Gu Lei Sun Paul H. Oyala James M. Rondinelli Danna E. Freedman 《Chemical science》2022,13(23):7034
The second quantum revolution harnesses exquisite quantum control for a slate of diverse applications including sensing, communication, and computation. Of the many candidates for building quantum systems, molecules offer both tunability and specificity, but the principles to enable high temperature operation are not well established. Spin–lattice relaxation, represented by the time constant T1, is the primary factor dictating the high temperature performance of quantum bits (qubits), and serves as the upper limit on qubit coherence times (T2). For molecular qubits at elevated temperatures (>100 K), molecular vibrations facilitate rapid spin–lattice relaxation which limits T2 to well below operational minimums for certain quantum technologies. Here we identify the effects of controlling orbital angular momentum through metal coordination geometry and ligand rigidity via π-conjugation on T1 relaxation in three four-coordinate Cu2+S = ½ qubit candidates: bis(N,N′-dimethyl-4-amino-3-penten-2-imine) copper(ii) (Me2Nac)2 (1), bis(acetylacetone)ethylenediamine copper(ii) Cu(acacen) (2), and tetramethyltetraazaannulene copper(ii) Cu(tmtaa) (3). We obtain significant T1 improvement upon changing from tetrahedral to square planar geometries through changes in orbital angular momentum. T1 is further improved with greater π-conjugation in the ligand framework. Our electronic structure calculations reveal that the reduced motion of low energy vibrations in the primary coordination sphere slows relaxation and increases T1. These principles enable us to report a new molecular qubit candidate with room temperature T2 = 0.43 μs, and establishes guidelines for designing novel qubit candidates operating above 100 K.Elucidating the role of specific vibrational modes in spin lattice relaxation is a key step to designing room temperature qubits. We executed an experimental and theoretical study on a series of Cu2+ qubits to increase their operating temperature. 相似文献
15.
Jeremy M. Kaminski Angela Rodríguez-Serrano Fabian Dinkelbach Hector Miranda-Salinas Andrew P. Monkman Christel M. Marian 《Chemical science》2022,13(23):7057
Quantum chemical studies employing combined density functional and multireference configuration interaction methods suggest five excited electronic states to be involved in the prompt and delayed fluorescence emission of TpAT-tFFO. Three of them, a pair of singlet and triplet charge transfer (CT) states (S1 and T1) and a locally excited (LE) triplet state (T3), can be associated with the (Me → N) conformer, the other two CT-type states (S2 and T2) form the lowest excited singlet and triplet states of the (Me → Ph) conformer. The two conformers, which differ in essence by the shearing angle of the face-to-face aligned donor and acceptor moieties, are easily interconverted in the electronic ground state whereas the reorganization energy is substantial in the excited singlet state, thus explaining the two experimentally observed time constants of prompt fluorescence emission. Forward and reverse intersystem crossing between the singlet and triplet CT states is mediated by vibronic spin–orbit interactions involving the LE T3 state. Low-frequency vibrational modes altering the distance and alignment of the donor and acceptor π-systems tune the S1 and T3 states (likewise S2 and T3) into and out of resonance. The enhancement of intersystem crossing due to the interplay of vibronic and spin–orbit coupling is considered a general feature of organic through-space charge-transfer thermally activated delayed fluorescence emitters.DFT/MRCI quantum chemical studies suggest five excited electronic states to be involved in the prompt and delayed fluorescence emission of TpAT-tFFO. 相似文献
16.
Anthony P. Deziel Matthew R. Espinosa Ljiljana Pavlovic David J. Charboneau Nilay Hazari Kathrin H. Hopmann Brandon Q. Mercado 《Chemical science》2022,13(8):2391
The insertion of carbon dioxide into metal element σ-bonds is an important elementary step in many catalytic reactions for carbon dioxide valorization. Here, the insertion of carbon dioxide into a family of group 10 alkyl complexes of the type (RPBP)M(CH3) (RPBP = B(NCH2PR2)2C6H4−; R = Cy or tBu; M = Ni or Pd) to generate κ1-acetate complexes of the form (RPBP)M{OC(O)CH3} is investigated. This involved the preparation and characterization of a number of new complexes supported by the unusual RPBP ligand, which features a central boryl donor that exerts a strong trans-influence, and the identification of a new decomposition pathway that results in C–B bond formation. In contrast to other group 10 methyl complexes supported by pincer ligands, carbon dioxide insertion into (RPBP)M(CH3) is facile and occurs at room temperature because of the high trans-influence of the boryl donor. Given the mild conditions for carbon dioxide insertion, we perform a rare kinetic study on carbon dioxide insertion into a late-transition metal alkyl species using (tBuPBP)Pd(CH3). These studies demonstrate that the Dimroth–Reichardt parameter for a solvent correlates with the rate of carbon dioxide insertion and that Lewis acids do not promote insertion. DFT calculations indicate that insertion into (tBuPBP)M(CH3) (M = Ni or Pd) proceeds via an SE2 mechanism and we compare the reaction pathway for carbon dioxide insertion into group 10 methyl complexes with insertion into group 10 hydrides. Overall, this work provides fundamental insight that will be valuable for the development of improved and new catalysts for carbon dioxide utilization.The kinetics of carbon dioxide insertion into a pincer-supported palladium methyl complex are studied. The complex inserts carbon dioxide at room temperature, and we explore both solvent and Lewis acid effects on carbon dioxide insertion. 相似文献
17.
Mitsushiro Nomura Noriko SakamotoHirokazu Nakajima Chikako Fujita-TakayamaToru Sugiyama Masatsugu Kajitani 《Polyhedron》2011,30(17):2890-2895
Azido coordinated dithiolene complexes [CpCo(N3){S2C2(CO2Me)2}(S-CHR1R2)], where R1, R2 = H (4a); R1 = H, R2 = SiMe3 (4b); R1 = H, R2 = CO2Et (4c), were synthesized by the reactions of the corresponding Cl− coordinated precursors [CpCo(Cl){S2C2(CO2Me)2}(S-CHR1R2)] (3a-3c) with sodium azide. The Cl− coordinated complex 3d (R1, R2 = CO2Me) did not produce any N3− coordinated complexes but formed the CR1R2-bridged alkylidene adduct [CpCo{S2C2(CO2Me)2}(CR1R2)] (2d; R1, R2 = CO2Me). The structure of 4a was determined by X-ray diffraction study. In the molecular structure of 4a, the coordinated N3− ligand and CHR1R2 group were located at the same side with respect to the dithiolene ring (syn form), although the corresponding Cl− precursor (3a; R1, R2 = H) was anti form. A structural conversion of syn/anti was conceivable during the Cl−/N3− ligand exchange. Thermal (80 °C) and photochemical reactions (Hg lamp) of 4a-4c were performed. Among them, 4c was relatively well reacted compared with the others to form the CR1R2-bridged alkylidene adduct (2c; R1 = H, R2 = CO2Et), followed by a formal HN3 elimination, and the reaction also produced non-adduct of the cobalt dithiolene complex [CpCo{S2C2(CO2Me)2}] (1). The electrochemical 1e− reduction of 4c underwent a formal N3− ligand elimination, and successive second reduction caused the CHR1R2 group elimination or reformed the CR1R2-bridged alkylidene adduct 2c. 相似文献
18.
Described herein is a dirhodium(ii)-catalyzed asymmetric cycloisomerization reaction of azaenyne through a cap-tether synergistic modulation strategy, which represents the first catalytic asymmetric cycloisomerization of azaenyne. This reaction is highly challenging because of its inherent strong background reaction leading to racemate formation and the high capability of coordination of the nitrogen atom resulting in catalyst deactivation. Varieties of centrally chiral isoindazole derivatives could be prepared in up to 99 : 1 d.r., 99 : 1 er and 99% yield and diverse enantiomerically enriched atropisomers bearing two five-membered heteroaryls have been accessed by using an oxidative central-to-axial chirality transfer strategy. The tethered nitrogen atom incorporated into the starting materials enabled easy late-modifications of the centrally and axially chiral products via C–H functionalizations, which further demonstrated the appealing synthetic utilities of this powerful asymmetric cyclization.Rh(ii)-catalyzed asymmetric cycloisomerization of azaenyne through a cap-tether synergistic modulation strategy was described. Diverse centrally and axially chiral isoindazoles were prepared and directed C–H late-stage modifications were developed.Known as one of the most significant and reliable access methods to chiral heterocycles, asymmetric cycloisomerization of conjugated enyne has caught extensive attention and interest for its wide applications in synthetic route design and mechanistic investigation.1 Specifically, asymmetric cyclization of conjugated enynone (X = C, Z = O) has been successfully developed and applied to the rapid construction of various chiral furan-containing skeletons with high efficiency in an extremely operationally simple manner (Scheme 1a).2 However, compared to the fruitful research with enynone, it is surprising that the analogous asymmetric version of azaenyne (Z = N–R) still remains underdeveloped.3 In fact, no successful example of catalytic asymmetric cyclization of azaenyne has been reported in the literature despite the apparent significance of nitrogen-containing five-membered heterocycles in the synthetic and pharmaceutical community.4 In 2004, Haley and Herges reported a detailed experimental and theoretical study of the cyclization reaction of (2-ethynylphenyl)-phenyldiazene, which is a unique azaenyne.5 According to the DFT calculations, very close and low activation barriers for 5-exo-dig and 6-endo-dig cyclization pathways under catalyst-free conditions were found, which shed light on the inherent challenges of the asymmetric reaction of azaenyne (Scheme 1b). For instance, there was usually a regioselectivity issue (5-exo and 6-endo) in the cyclization reaction of azaenyne because of their close reaction barriers where the competitive 6-endo-dig cyclization3a,6 may lead to troublesome side-product formation. In addition, the low activation barrier deriving from the strong N-nucleophilicity of azaenyne may easily lead to self-cyclization which will cause severe background reactions to interfere with the asymmetric process. More troublingly, this transformation might suffer from catalyst deactivation arising from the high coordinating capability of the nitrogen atom in both starting materials and products, which might give more opportunities to the propagation of detrimental background reactions. In some cases, even a super-stoichiometric amount of transition metal has to be used to ensure effective conversion.3a,7 Therefore, although many nonchiral approaches have been reported,3,5 catalytic asymmetric cyclization of azaenyne still remains elusive due to the inherent obstacles aforementioned. With our continuous interest in alkyne chemistry,2a,8 herein we designed a cap-tether synergistic modulation strategy to tackle these challenges, envisioning that modulation of the tethered atom and protecting cap of nitrogen in the azaenyne would intrinsically perturb and alter the reactivity of the starting material, and therefore the azaenyne motif could be effectively harnessed as a promising synthon for asymmetric transformations (Scheme 1c). It should be noted that the obtained centrally chiral product produced from intramolecular C–H insertion of donor-type metal carbene9 might be potentially converted into the axially chiral molecule via a central-to-axial chirality conversion strategy.Open in a separate windowScheme 1Development of the asymmetric cyclization reaction of conjugated azaenyne.With this design in mind, different types of azaenynes bearing typical tethering atoms and capping groups were chosen to test our hypothesis and representative results are shown in Scheme 2. First, tBu-capping imine (X = C, R = tBu) was selected as a substrate to test our hypothesis.6a It was found that the imine exhibited low reactivity and the reaction temperature has to be elevated to 100 °C to initiate the transformation with or without catalyst. Unfortunately, the desired 5-exo-dig cyclization product was not detected, but isoquinoline from 6-endo-dig cyclization was obtained instead (Scheme 2a). To further regulate and control the regioselectivity and reactivity, triazene (X = N, R = N-piperidyl) was then investigated. Similarly, this substrate also showed low reactivity and it is still required to be heated at 100 °C for conversion. In the absence of a metal catalyst, an unexpected alkyne, deriving from the fragmentation of the triazene moiety, was produced in 41% yield. When 2 mol% Rh2(OPiv)4 was added as a catalyst, the side reaction could be efficiently suppressed and the reaction selectivity was apparently reversed. In this case, the target C–H insertion dihydrofuran was furnished as the major product in 30% yield but still accompanied by concomitant formation of 12% yield of undesired alkyne (Scheme 2b). The above investigations showed neither the imine nor triazene was an ideal substrate for the asymmetric reaction. Thus, we moved our attention to the diazene substrate (X = N, R = aryl). As demonstrated by Haley''s and Herges'' pioneering work, ortho-alkynyl diazene, compared with imine and triazene, was more unstable and tended to self-cyclization even at room temperature.5a As shown in Scheme 2c, the ortho-alkynyl diazene degrades and 5-exo-dig cyclization products could be observed even in DCE solvent without any catalyst at room temperature. When the phenyl capping group was installed in the substrate, the reaction furnished 10% yield of isoindazole derivative. The uncatalyzed self-cyclization reaction was obviously accelerated when an electron-rich capping group (4-MeO–C6H4–) was introduced, affording the corresponding product in 20% yield. Inspired by these findings, we assumed that installation of an electron deficient group on the capping phenyl would reduce the nucleophilicity of the nitrogen atom and thus the troublesome self-cyclization reaction might be effectively inhibited. To our delight, when a bromo-substituent was introduced onto the phenyl cap, the undesired self-cyclization was almost suppressed. When Rh2(OPiv)4 was added as a catalyst, the desired carbene-involved C–H insertion product was furnished in 90% yield at room temperature. Worthy of note was the total absence of any cinnoline formation from 6-endo-dig cyclization.3a,6b In short, the synthetic challenges associated with regioselectivity (5-exo-dig and 6-endo-dig), strong background reaction and catalyst deactivation could be successfully regulated and controlled via a tether-cap synergistic modulation strategy.Open in a separate windowScheme 2Typical substrate investigation.Encouraged by the above findings, ortho-alkynyl bromodiazene 1a was chosen as a model substrate and different types of chiral dirhodium catalysts10 were screened in DCE at room temperature for 48 h. As shown in Entry Rh(ii)* Solvent Yieldb [%] erc 1 Rh2(R-DOSP)4 DCE 56 29 : 71 2 Rh2(5S-MEPY)4 DCE 17 50 : 50 3 Rh2(S-BTPCP)4 DCE 61 8 : 92 4 Rh2(S-PTPA)4 DCE 91 91 : 9 5 Rh2(S-PTTL)4 DCE 86 97 : 3 6 Rh2(S-PTAD)4 DCE 93 94 : 6 7 Rh2(S-NTTL)4 DCE 92 96 : 4 8 Rh2(S-TCPTTL)4 DCE 95 98 : 2 9 Rh 2 (S-TFPTTL) 4 DCE 98 d 98 : 2 10 Rh2(S-TFPTTL)4 DCM 88 98 : 2 11 Rh2(S-TFPTTL)4 Toluene 92 98 : 2 12 Rh2(S-TFPTTL)4 MeCN 16 92 : 8 13 Rh2(S-TFPTTL)4 n-Hexane 96 98 : 2 14e Rh2(S-TFPTTL)4 DCE 65f 96 : 4