Pub Date : 2024-02-28DOI: 10.1021/acs.accounts.4c00006
Zhaoming Zhang, Jun Zhao and Xuzhou Yan*,
Mechanically interlocked polymers (MIPs) such as polyrotaxanes and polycatenanes are polymer architectures that incorporate mechanical bonds, which represent a compelling frontier in polymer science. MIPs with cross-linked structures are known as mechanically interlocked networks (MINs) and are widely utilized in materials science. Leveraging the motion of mechanical bonds, MINs hold the potential for achieving a combination of robustness and dynamicity. Currently, the reported MINs predominantly consist of networks with discrete mechanical bonds as cross-linking points, exemplified by well-known slide-ring materials and rotaxane/catenane cross-linked polymers. The motion of these mechanically interlocked cross-linking points facilitates the redistribution of tension throughout the network, effectively preventing stress concentration and thereby enhancing material toughness. In these instances, the impact of mechanical bonds can be likened to the adage “small things can make a big difference”, whereby a limited number of mechanical bonds substantially elevate the mechanical performance of conventional polymers. In addition to MINs cross-linked by mechanical bonds, there is another type of MIN in which their principal parts are polymer chains composed of dense mechanical bonds. Within these MINs, mechanical bonds generally serve as repeating units, and their unique properties stem from integrating and amplifying the function of a large amount of mechanical bonds. Consequently, MINs with dense mechanical bonds tend to reflect the intrinsic properties of mechanical interlocked polymers, making their exploration critical for a comprehensive understanding of MIPs. Nevertheless, investigations into MINs featuring dense mechanical bonds remain relatively scarce.
This Account presents a comprehensive overview of our investigation and insights into MINs featuring dense mechanical bonds. First, we delve into the synthetic strategies employed to effectively prepare MINs with dense mechanical bonds, while critically evaluating their advantages and limitations. Through meticulous control of the core interlocking step, three distinct strategies have emerged: mechanical interlocking followed by polymerization, supramolecular polymerization followed by mechanical interlocking, and dynamic interlocking. Furthermore, we underscore the structure–property relationships of MINs with dense mechanical bonds. The macroscopic properties of MINs originate from integrating and amplifying countless microscopic motions of mechanical bonds, a phenomenon we define as an integration and amplification mechanism. Our investigation has revealed detailed motion characteristics of mechanical bonds in bulk mechanically interlocked materials, encompassing the quantification of motion activation energy, discrimination of varying motion distances, and elucidation of the recovery process. Additionally, we have elucidated their influence on the mechanical performance of the res
摘要机械互锁聚合物(MIPs),如聚罗他赛和聚卡他烯酮,是一种含有机械键的聚合物结构,代表了聚合物科学中一个引人注目的前沿领域。具有交联结构的 MIP 被称为机械互锁网络 (MIN),广泛应用于材料科学领域。利用机械键的运动,MINs 有可能实现稳健性和动态性的结合。目前,已报道的 MINs 主要由以离散机械键作为交联点的网络组成,例如著名的滑环材料和罗他烷/卡替萘交联聚合物。这些机械交联点的运动有助于整个网络中张力的重新分配,有效防止应力集中,从而提高材料的韧性。在这种情况下,机械键的影响就好比 "以小见大 "这句谚语,数量有限的机械键可大大提高传统聚合物的机械性能。除了通过机械键交联的 MIN 外,还有一种 MIN,其主要部分是由密集机械键组成的聚合物链。在这些 MIN 中,机械键通常作为重复单元,其独特性能源于整合和放大了大量机械键的功能。因此,具有致密机械键的 MINs 往往反映了机械交错聚合物的固有特性,因此对它们的研究对于全面了解 MIPs 至关重要。然而,对具有致密机械键的 MINs 的研究仍然相对较少。本篇开户绑定手机领体验金全面概述了我们对具有致密机械键的 MINs 的研究和见解。首先,我们深入探讨了有效制备具有致密机械键的 MINs 所采用的合成策略,同时批判性地评估了这些策略的优势和局限性。通过对核心互锁步骤的细致控制,我们发现了三种不同的策略:先机械互锁后聚合、先超分子聚合后机械互锁以及动态互锁。此外,我们还强调了具有致密机械键的 MINs 的结构-性能关系。MINs 的宏观特性源于对无数机械键微观运动的整合与放大,我们将这种现象定义为整合与放大机制。我们的研究揭示了块状机械互锁材料中机械键的详细运动特征,包括运动活化能的量化、不同运动距离的判别以及恢复过程的阐明。此外,我们还阐明了它们对相应材料机械性能的影响。此外,我们还利用 MINs 卓越的机械性能和动态性,探索了 MINs 的潜在应用领域。这些应用包括增强传统聚合物的韧性、设计具有机械适应性的多功能气凝胶,以及在锂离子电池中作为界面层减轻锂突起。最后,我们就具有致密机械键的 MINs 的未来发展前景、机遇和主要挑战提出了个人观点,强调了这一新兴领域取得变革性进展的潜力。
{"title":"Mechanically Interlocked Polymers with Dense Mechanical Bonds","authors":"Zhaoming Zhang, Jun Zhao and Xuzhou Yan*, ","doi":"10.1021/acs.accounts.4c00006","DOIUrl":"10.1021/acs.accounts.4c00006","url":null,"abstract":"<p >Mechanically interlocked polymers (MIPs) such as polyrotaxanes and polycatenanes are polymer architectures that incorporate mechanical bonds, which represent a compelling frontier in polymer science. MIPs with cross-linked structures are known as mechanically interlocked networks (MINs) and are widely utilized in materials science. Leveraging the motion of mechanical bonds, MINs hold the potential for achieving a combination of robustness and dynamicity. Currently, the reported MINs predominantly consist of networks with discrete mechanical bonds as cross-linking points, exemplified by well-known slide-ring materials and rotaxane/catenane cross-linked polymers. The motion of these mechanically interlocked cross-linking points facilitates the redistribution of tension throughout the network, effectively preventing stress concentration and thereby enhancing material toughness. In these instances, the impact of mechanical bonds can be likened to the adage “small things can make a big difference”, whereby a limited number of mechanical bonds substantially elevate the mechanical performance of conventional polymers. In addition to MINs cross-linked by mechanical bonds, there is another type of MIN in which their principal parts are polymer chains composed of dense mechanical bonds. Within these MINs, mechanical bonds generally serve as repeating units, and their unique properties stem from integrating and amplifying the function of a large amount of mechanical bonds. Consequently, MINs with dense mechanical bonds tend to reflect the intrinsic properties of mechanical interlocked polymers, making their exploration critical for a comprehensive understanding of MIPs. Nevertheless, investigations into MINs featuring dense mechanical bonds remain relatively scarce.</p><p >This Account presents a comprehensive overview of our investigation and insights into MINs featuring dense mechanical bonds. First, we delve into the synthetic strategies employed to effectively prepare MINs with dense mechanical bonds, while critically evaluating their advantages and limitations. Through meticulous control of the core interlocking step, three distinct strategies have emerged: mechanical interlocking followed by polymerization, supramolecular polymerization followed by mechanical interlocking, and dynamic interlocking. Furthermore, we underscore the structure–property relationships of MINs with dense mechanical bonds. The macroscopic properties of MINs originate from integrating and amplifying countless microscopic motions of mechanical bonds, a phenomenon we define as an integration and amplification mechanism. Our investigation has revealed detailed motion characteristics of mechanical bonds in bulk mechanically interlocked materials, encompassing the quantification of motion activation energy, discrimination of varying motion distances, and elucidation of the recovery process. Additionally, we have elucidated their influence on the mechanical performance of the res","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":null,"pages":null},"PeriodicalIF":18.3,"publicationDate":"2024-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139988627","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-28DOI: 10.1021/acs.accounts.3c00667
Manuel Quiroz, and , Marcetta Y. Darensbourg*,
The ubiquity of sulfur–metal connections in nature inspires the design of bi- and multimetallic systems in synthetic inorganic chemistry. Common motifs for biocatalysts developed in evolutionary biology include the placement of metals in close proximity with flexible sulfur bridges as well as the presence of π-acidic/delocalizing ligands. This Account will delve into the development of a (NO)Fe(N2S2) metallodithiolate ligand that harnesses these principles. The Fe(NO) unit is the centroid of a N2S2 donor field, which as a whole is capable of serving as a redox-active, bidentate S-donor ligand. Its paramagnetism as well as the ν(NO) vibrational monitor can be exploited in the development of new classes of heterobimetallic complexes. We offer four examples in which the unpaired electron on the {Fe(NO)}7 unit is spin-paired with adjacent paramagnets in proximal and distal positions.
First, the exceptional stability of the (NO)Fe(N2S2)-Fe(NO)2 platform, which permits its isolation and structural characterization at three distinct redox levels, is linked to the charge delocalization occurring on both the Fe(NO) and the Fe(NO)2 supports. This accommodates the formation of a rare nonheme {Fe(NO)}8 triplet state, with a linear configuration. A subsequent FeNi complex, featuring redox-active ligands on both metals (NO on iron and dithiolene on nickel), displayed unexpected physical properties. Our research showed good reversibility in two redox processes, allowing isolation in reduced and oxidized forms. Various spectroscopic and crystallographic analyses confirmed these states, and Mössbauer data supported the redox change at the iron site upon reduction. Oxidation of the complex produced a dimeric dication, revealing an intriguing magnetic behavior. The monomer appears as a spin-coupled diradical between {Fe(NO)}7 and the nickel dithiolene monoradical, while dimerization couples the latter radical units via a Ni2S2 rhomb. Magnetic data (SQUID) on the dimer dication found a singlet ground state with a thermally accessible triplet state that is responsible for magnetism. A theoretical model built on an H4 chain explains this unexpected ferromagnetic low-energy triplet state arising from the antiferromagnetic coupling of a four-radical molecular conglomerate. For comparison, two (NO)Fe(N2S2) were connected through diamagnetic group 10 cations producing diradical trimetallic complexes. Antiferromagnetic coupling is observed between {Fe(NO)}7 units, with exchange coupling constants (J) of −3, −23, and −124 cm–1 for NiII, PdII, and PtII, respectively. This trend is explained by the enhanced covalency and polarizability of sulfur-dense metallodithiolate ligands. A central paramagnetic trans-Cr(NO)(MeCN) recei
内容提要自然界中无处不在的硫金属连接激发了人们在合成无机化学中设计双金属和多金属系统的灵感。进化生物学中开发的生物催化剂的常见模式包括将金属与柔性硫桥紧密相连,以及存在π酸性/定位配体。本实验将深入研究利用这些原理开发的 (NO)Fe(N2S2) 金属二硫酸盐配体。Fe(NO)单元是一个 N2S2 供体场的中心,作为一个整体,它可以作为一种具有氧化还原活性的双齿 S 供体配体。它的顺磁性和 ν(NO)振动监测器可用于开发新型杂多金属配合物。首先,(NO)Fe(N2S2)-Fe(NO)2 平台的超强稳定性使其能够在三个不同的氧化还原水平下进行分离和结构表征,这与发生在 Fe(NO)和 Fe(NO)2 支持物上的电荷分离有关。这就形成了具有线性构型的稀有非血红素{Fe(NO)}8三重态。随后的铁镍复合物在两种金属上都具有氧化还原活性配体(铁上的 NO 和镍上的二硫环戊烯),显示出意想不到的物理性质。我们的研究表明,该复合物在两个氧化还原过程中具有良好的可逆性,可分离出还原型和氧化型复合物。各种光谱和晶体学分析证实了这些状态,而莫斯鲍尔数据则证明了还原过程中铁位点的氧化还原变化。该复合物氧化后产生了二聚二元化合物,揭示了一种引人入胜的磁性行为。单体显示为{Fe(NO)}7 和二硫代二环镍单体之间的自旋耦合二价,而二聚体则通过 Ni2S2 菱形结构将后者的自由基单元耦合在一起。关于二聚二阳离子的磁性数据(SQUID)发现了一个单线基态和一个可热处理的三线态,三线态是产生磁性的原因。建立在 H4 链上的理论模型解释了这一意想不到的铁磁性低能三重态,它产生于四基态分子团的反铁磁耦合。为了进行比较,两个 (NO)Fe(N2S2) 通过第 10 组二元阳离子连接,产生了二元三金属复合物。在{Fe(NO)}7单元之间观察到了反铁磁耦合,NiII、PdII和PtII的交换耦合常数(J)分别为-3、-23和-124 cm-1。硫密金属二硫酸盐配体增强的共价性和极化性解释了这一趋势。中央顺磁反式-Cr(NO)(MeCN)受体单元核心导致顺式结构拓扑,并受到硫供体上孤对子立体活性的影响。这种{Cr(NO)}5自由基桥与之前的所有情况都不同,它发现远端Fe(NO)自由基之间的耦合是铁磁性的(J = 24 cm-1)。这种 S = 1/2分子的稳定性和可预测性以及桥接硫代硫酸盐的立体/电子特性表明,它很可能成为开发新型分子(磁性)化合物和材料的候选材料。本研究强调了合成无机化学在设计可连接(NO)Fe(N2S2)金属配体的合成物中的作用,以及由此衍生的杂多金属复合物的特性。
{"title":"Development of (NO)Fe(N2S2) as a Metallodithiolate Spin Probe Ligand: A Case Study Approach","authors":"Manuel Quiroz, and , Marcetta Y. Darensbourg*, ","doi":"10.1021/acs.accounts.3c00667","DOIUrl":"10.1021/acs.accounts.3c00667","url":null,"abstract":"<p >The ubiquity of sulfur–metal connections in nature inspires the design of bi- and multimetallic systems in synthetic inorganic chemistry. Common motifs for biocatalysts developed in evolutionary biology include the placement of metals in close proximity with flexible sulfur bridges as well as the presence of π-acidic/delocalizing ligands. This Account will delve into the development of a (NO)Fe(N<sub>2</sub>S<sub>2</sub>) metallodithiolate ligand that harnesses these principles. The Fe(NO) unit is the centroid of a N<sub>2</sub>S<sub>2</sub> donor field, which as a whole is capable of serving as a redox-active, bidentate S-donor ligand. Its paramagnetism as well as the ν(NO) vibrational monitor can be exploited in the development of new classes of heterobimetallic complexes. We offer four examples in which the unpaired electron on the {Fe(NO)}<sup>7</sup> unit is spin-paired with adjacent paramagnets in proximal and distal positions.</p><p >First, the exceptional stability of the (NO)Fe(N<sub>2</sub>S<sub>2</sub>)-Fe(NO)<sub>2</sub> platform, which permits its isolation and structural characterization at three distinct redox levels, is linked to the charge delocalization occurring on both the Fe(NO) and the Fe(NO)<sub>2</sub> supports. This accommodates the formation of a rare nonheme {Fe(NO)}<sup>8</sup> triplet state, with a linear configuration. A subsequent FeNi complex, featuring redox-active ligands on both metals (NO on iron and dithiolene on nickel), displayed unexpected physical properties. Our research showed good reversibility in two redox processes, allowing isolation in reduced and oxidized forms. Various spectroscopic and crystallographic analyses confirmed these states, and Mössbauer data supported the redox change at the iron site upon reduction. Oxidation of the complex produced a dimeric dication, revealing an intriguing magnetic behavior. The monomer appears as a spin-coupled diradical between {Fe(NO)}<sup>7</sup> and the nickel dithiolene monoradical, while dimerization couples the latter radical units via a Ni<sub>2</sub>S<sub>2</sub> rhomb. Magnetic data (SQUID) on the dimer dication found a singlet ground state with a thermally accessible triplet state that is responsible for magnetism. A theoretical model built on an H<sub>4</sub> chain explains this unexpected ferromagnetic low-energy triplet state arising from the antiferromagnetic coupling of a four-radical molecular conglomerate. For comparison, two (NO)Fe(N<sub>2</sub>S<sub>2</sub>) were connected through diamagnetic group 10 cations producing diradical trimetallic complexes. Antiferromagnetic coupling is observed between {Fe(NO)}<sup>7</sup> units, with exchange coupling constants (<i>J</i>) of −3, −23, and −124 cm<sup>–1</sup> for Ni<sup>II</sup>, Pd<sup>II</sup>, and Pt<sup>II</sup>, respectively. This trend is explained by the enhanced covalency and polarizability of sulfur-dense metallodithiolate ligands. A central paramagnetic <i>trans</i>-Cr(NO)(MeCN) recei","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":null,"pages":null},"PeriodicalIF":18.3,"publicationDate":"2024-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139988601","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Cancer vaccines have shown tremendous potential in preventing and treating cancer by providing immunogenic antigens to initiate specific tumor immune responses. An in situ vaccine prepared from an autologous tumor can mobilize a patient’s own tumor cell lysate as a reservoir of specific antigens, thus triggering a broad immune response and diverse antitumor immunity in an individually tailored manner. Its efficacy is much better than that of conventional vaccines with a limited number of epitopes. Several conventional therapies, including radiotherapy (RT), chemotherapeutics, photodynamic therapy (PDT), and photothermal therapy (PTT) can activate an anticancer in situ vaccine response by inducing immunogenic cell death (ICD), triggering the exposure of tumor-associated antigens (TAAs), cancerous testis antigens, neoantigens, and danger-associated molecular patterns (DAMPs) with low cost. However, the immunogenicity of dying tumor cells is low, making released antigens and DAMPs insufficient to initiate a robust immune response against malignant cancer. Moreover, the immunosuppressive tumor microenvironment (TME) severely hinders the infiltration and sensitization of effector immune cells, causing tolerogenic immunological effects.
Herein, we mainly focus on the research in developing nanoplatforms to surmount the major challenges met by ICD-based in situ vaccines. We first summarized a variety of nanotechnologies that enable enhanced immunogenicity of dying cancer cells by enhancing antigenicity and adjuvanticity. The robust antigenicity was obtained via regulating the tumor cells death mode or the dying state to amplify the recognition of tumor debris by professional antigen-presenting cells (APCs). The adjuvanticity was potentiated by raising the level or intensifying the activity of endogenous adjuvants or promoting the intelligent delivery of exogenous immunostimulants to activate immune cell recruitment and promote antigen presentation. Additionally, versatile approaches to reverse immunosuppressive TME to boost the in situ tumor vaccination response are also highlighted in detail. On one hand, by modulating the cell metabolism in TME, the expansion and activity of effector versus immunosuppressive cells can be optimized to improve the efficiency of in situ vaccines. On the other hand, regulating cellular components in TME, such as reversing adverse immune cell phenotypes or inhibiting the activity of interstitial cells, can also significantly enhance the ICD-based antitumor immunotherapy effect. Finally, our viewpoint on the future challenges and opportunities in this hopeful area is presented. We expect that this Account can offer much more insight into the design, planning, and development of cutting-edge in situ tumor vaccine platforms, promoting more attention and academic–industry collaborations, accelerating the advanced progress of in situ tumor vaccine-based immunotherapy i
{"title":"Nanomedicines for an Enhanced Immunogenic Cell Death-Based In Situ Cancer Vaccination Response","authors":"Caiyan Zhao, Changrong Wang, Wenbo Shan, Zhongliang Wang*, Xiaoyuan Chen* and Hongzhang Deng*, ","doi":"10.1021/acs.accounts.3c00771","DOIUrl":"10.1021/acs.accounts.3c00771","url":null,"abstract":"<p >Cancer vaccines have shown tremendous potential in preventing and treating cancer by providing immunogenic antigens to initiate specific tumor immune responses. An <i>in situ</i> vaccine prepared from an autologous tumor can mobilize a patient’s own tumor cell lysate as a reservoir of specific antigens, thus triggering a broad immune response and diverse antitumor immunity in an individually tailored manner. Its efficacy is much better than that of conventional vaccines with a limited number of epitopes. Several conventional therapies, including radiotherapy (RT), chemotherapeutics, photodynamic therapy (PDT), and photothermal therapy (PTT) can activate an anticancer <i>in situ</i> vaccine response by inducing immunogenic cell death (ICD), triggering the exposure of tumor-associated antigens (TAAs), cancerous testis antigens, neoantigens, and danger-associated molecular patterns (DAMPs) with low cost. However, the immunogenicity of dying tumor cells is low, making released antigens and DAMPs insufficient to initiate a robust immune response against malignant cancer. Moreover, the immunosuppressive tumor microenvironment (TME) severely hinders the infiltration and sensitization of effector immune cells, causing tolerogenic immunological effects.</p><p >Herein, we mainly focus on the research in developing nanoplatforms to surmount the major challenges met by ICD-based <i>in situ</i> vaccines. We first summarized a variety of nanotechnologies that enable enhanced immunogenicity of dying cancer cells by enhancing antigenicity and adjuvanticity. The robust antigenicity was obtained via regulating the tumor cells death mode or the dying state to amplify the recognition of tumor debris by professional antigen-presenting cells (APCs). The adjuvanticity was potentiated by raising the level or intensifying the activity of endogenous adjuvants or promoting the intelligent delivery of exogenous immunostimulants to activate immune cell recruitment and promote antigen presentation. Additionally, versatile approaches to reverse immunosuppressive TME to boost the <i>in situ</i> tumor vaccination response are also highlighted in detail. On one hand, by modulating the cell metabolism in TME, the expansion and activity of effector versus immunosuppressive cells can be optimized to improve the efficiency of <i>in situ</i> vaccines. On the other hand, regulating cellular components in TME, such as reversing adverse immune cell phenotypes or inhibiting the activity of interstitial cells, can also significantly enhance the ICD-based antitumor immunotherapy effect. Finally, our viewpoint on the future challenges and opportunities in this hopeful area is presented. We expect that this Account can offer much more insight into the design, planning, and development of cutting-edge <i>in situ</i> tumor vaccine platforms, promoting more attention and academic–industry collaborations, accelerating the advanced progress of <i>in situ</i> tumor vaccine-based immunotherapy i","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":null,"pages":null},"PeriodicalIF":18.3,"publicationDate":"2024-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139988626","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-27DOI: 10.1021/acs.accounts.3c00774
Ian J. S. Fairlamb*, and , Jason M. Lynam*,
An understanding of the mechanistic processes that underpin reactions catalyzed by 3d transition metals is vital for their development as potential replacements for scarce platinum group metals. However, this is a significant challenge because of the tendency of 3d metals to undergo mechanistically diverse pathways when compared with their heavier congeners, often as a consequence of one-electron transfer reactions and/or intrinsically weaker metal–ligand bonds. We have developed and implemented a new methodology to illuminate the pathways that underpin C–H bond functionalization pathways in reactions catalyzed by Mn–carbonyl compounds. By integrating measurements performed on catalytic reactions with in situ reaction monitoring and state-of-the-art ultrafast spectroscopic methods, unique insight into the mode of action and fate of the catalyst have been obtained.
Using a combination of time-resolved spectroscopy and in situ low-temperature NMR studies, we have shown that photolysis of manganese–carbonyl precatalysts results in rapid (<5 ps) CO dissociation─the same process that occurs under thermal catalytic conditions. This enabled the detection of the key states relevant to catalysis, including solvent and alkyne complexes and their resulting transformation into manganacycles, which results from a migratory insertion reaction into the Mn–C bond. By systematic variation of the substrates (many of which are real-world structurally diverse substrates and not simple benchmark systems) and quantification of the resulting rate constants for the insertion step, a universal model for this migratory insertion process has been developed. The time-resolved spectroscopic method gave insight into fundamental mechanistic pathways underpinning other aspects of modern synthetic chemistry. The most notable was the first direct experimental observation of the concerted metalation deprotonation (CMD) mechanism through which carboxylate groups are able to mediate C–H bond activation at a metal center. This step underpins a host of important synthetic applications. This study demonstrated how the time-resolved multiple probe spectroscopy (TRMPS) method enables the observation of mechanistic process occurring on time scales from several picoseconds through to μs in a single experiment, thereby allowing the sequential observation of solvation, ligand substitution, migratory insertion, and ultimate protonation of a Mn–C bond.
These studies have been complemented by an investigation of the “in reaction flask” catalyst behavior, which has provided additional insight into new pathways for precatalyst activation, including evidence that alkyne C–H bond activation may occur before heterocycle activation. Crucial insight into the fate of the catalyst species showed that excess water played a key role in deactivation to give higher-order hydroxyl-bridged manganese carbonyl clusters, which were independently found to be inactive. Traditional i
{"title":"Unveiling Mechanistic Complexity in Manganese-Catalyzed C–H Bond Functionalization Using IR Spectroscopy Over 16 Orders of Magnitude in Time","authors":"Ian J. S. Fairlamb*, and , Jason M. Lynam*, ","doi":"10.1021/acs.accounts.3c00774","DOIUrl":"10.1021/acs.accounts.3c00774","url":null,"abstract":"<p >An understanding of the mechanistic processes that underpin reactions catalyzed by 3d transition metals is vital for their development as potential replacements for scarce platinum group metals. However, this is a significant challenge because of the tendency of 3d metals to undergo mechanistically diverse pathways when compared with their heavier congeners, often as a consequence of one-electron transfer reactions and/or intrinsically weaker metal–ligand bonds. We have developed and implemented a new methodology to illuminate the pathways that underpin C–H bond functionalization pathways in reactions catalyzed by Mn–carbonyl compounds. By integrating measurements performed on catalytic reactions with in situ reaction monitoring and state-of-the-art ultrafast spectroscopic methods, unique insight into the mode of action and fate of the catalyst have been obtained.</p><p >Using a combination of time-resolved spectroscopy and in situ low-temperature NMR studies, we have shown that photolysis of manganese–carbonyl precatalysts results in rapid (<5 ps) CO dissociation─the same process that occurs under thermal catalytic conditions. This enabled the detection of the key states relevant to catalysis, including solvent and alkyne complexes and their resulting transformation into manganacycles, which results from a migratory insertion reaction into the Mn–C bond. By systematic variation of the substrates (many of which are real-world structurally diverse substrates and not simple benchmark systems) and quantification of the resulting rate constants for the insertion step, a universal model for this migratory insertion process has been developed. The time-resolved spectroscopic method gave insight into fundamental mechanistic pathways underpinning other aspects of modern synthetic chemistry. The most notable was the first direct experimental observation of the concerted metalation deprotonation (CMD) mechanism through which carboxylate groups are able to mediate C–H bond activation at a metal center. This step underpins a host of important synthetic applications. This study demonstrated how the time-resolved multiple probe spectroscopy (TR<sup>M</sup>PS) method enables the observation of mechanistic process occurring on time scales from several picoseconds through to μs in a single experiment, thereby allowing the sequential observation of solvation, ligand substitution, migratory insertion, and ultimate protonation of a Mn–C bond.</p><p >These studies have been complemented by an investigation of the “in reaction flask” catalyst behavior, which has provided additional insight into new pathways for precatalyst activation, including evidence that alkyne C–H bond activation may occur before heterocycle activation. Crucial insight into the fate of the catalyst species showed that excess water played a key role in deactivation to give higher-order hydroxyl-bridged manganese carbonyl clusters, which were independently found to be inactive. Traditional i","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":null,"pages":null},"PeriodicalIF":18.3,"publicationDate":"2024-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://pubs.acs.org/doi/epdf/10.1021/acs.accounts.3c00774","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139981980","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-25DOI: 10.1021/acs.accounts.3c00761
Mingzhu Liu*, and , Shu Yang*,
The intrinsic molecular order of liquid crystals (LCs) and liquid crystalline elastomers (LCEs) is the origin of their stimuli-responsive properties. The programmable responsiveness and functionality, such as shape morphing and color change under external stimuli, are the key features that attract interest in designing LC- and LCE-based intelligent material platforms. Methods such as mechanical stretching and shearing, surface alignment, and field-assisted alignment have been exploited to program the order of LC molecules for the desired responsiveness. However, the huge size mismatch between the nanometer-sized LC mesogens and the targeted macroscopic objects calls for questions about how to delicately control molecular order for desired performance. Microparticles that can be synthesized with intrinsic molecular order precisely controlled to micrometer size can be used as building blocks for bulk materials, thus offering opportunities to bridge the gap and transcend molecular orders across scales. By taking advantage of the interfacial anchoring effects, we can control and engineer the molecular orders inside the microdroplets, allowing for the realization of various responsive behaviors. Furthermore, designer LC microparticles with multiple responsiveness can be assembled and confined within a matrix, opening a new pathway to engineering LC-enabled intelligent materials.
In this Account, we present our recent work on exploiting the molecular order inside microdroplets for the construction of intelligent materials. We briefly introduce the typical chemicals used in the synthesis and the methods developed to control LC molecular alignment within a microdroplets. We then present examples of microparticles synthesized from microdroplets that can transform into complex morphologies upon cooling from the isotropic to nematic phase or due to phase separation within the droplets coupled with the segregation of LC oligomers (LCOs) with polydisperse chain lengths. Furthermore, we show the synthesis of elliptical LCE microparticles and exploit their thermal and magnetic responsiveness to program shape-morphing behaviors and microarrays with switchable optical polarization. By mixing magnetic nanoparticles in cholesteric liquid crystals (CLCs) and silicone oils, we created Janus microparticles capable of color switching for camouflage and information encryption. Moreover, we can engineer complex molecular orders in LCE microparticles by mixing different surfactants, yielding microparticles of diverse anisotropic, temperature-responsive shapes after photopolymerization and extraction of the template LC molecules with different solvents. We conclude the Account with an outlook on the design of intelligent material systems via the design of unprecedented molecular ordering within the microparticles and their coupling with bulk materials.
{"title":"Exploiting Molecular Orders at the Interface of Microdroplets for Intelligent Materials","authors":"Mingzhu Liu*, and , Shu Yang*, ","doi":"10.1021/acs.accounts.3c00761","DOIUrl":"10.1021/acs.accounts.3c00761","url":null,"abstract":"<p >The intrinsic molecular order of liquid crystals (LCs) and liquid crystalline elastomers (LCEs) is the origin of their stimuli-responsive properties. The programmable responsiveness and functionality, such as shape morphing and color change under external stimuli, are the key features that attract interest in designing LC- and LCE-based intelligent material platforms. Methods such as mechanical stretching and shearing, surface alignment, and field-assisted alignment have been exploited to program the order of LC molecules for the desired responsiveness. However, the huge size mismatch between the nanometer-sized LC mesogens and the targeted macroscopic objects calls for questions about how to delicately control molecular order for desired performance. Microparticles that can be synthesized with intrinsic molecular order precisely controlled to micrometer size can be used as building blocks for bulk materials, thus offering opportunities to bridge the gap and transcend molecular orders across scales. By taking advantage of the interfacial anchoring effects, we can control and engineer the molecular orders inside the microdroplets, allowing for the realization of various responsive behaviors. Furthermore, designer LC microparticles with multiple responsiveness can be assembled and confined within a matrix, opening a new pathway to engineering LC-enabled intelligent materials.</p><p >In this Account, we present our recent work on exploiting the molecular order inside microdroplets for the construction of intelligent materials. We briefly introduce the typical chemicals used in the synthesis and the methods developed to control LC molecular alignment within a microdroplets. We then present examples of microparticles synthesized from microdroplets that can transform into complex morphologies upon cooling from the isotropic to nematic phase or due to phase separation within the droplets coupled with the segregation of LC oligomers (LCOs) with polydisperse chain lengths. Furthermore, we show the synthesis of elliptical LCE microparticles and exploit their thermal and magnetic responsiveness to program shape-morphing behaviors and microarrays with switchable optical polarization. By mixing magnetic nanoparticles in cholesteric liquid crystals (CLCs) and silicone oils, we created Janus microparticles capable of color switching for camouflage and information encryption. Moreover, we can engineer complex molecular orders in LCE microparticles by mixing different surfactants, yielding microparticles of diverse anisotropic, temperature-responsive shapes after photopolymerization and extraction of the template LC molecules with different solvents. We conclude the Account with an outlook on the design of intelligent material systems via the design of unprecedented molecular ordering within the microparticles and their coupling with bulk materials.</p>","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":null,"pages":null},"PeriodicalIF":18.3,"publicationDate":"2024-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139970164","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-23DOI: 10.1021/acs.accounts.4c00009
Huanhuan Jia, Zhenda Tan and Min Zhang*,
The selective functionalization/transformation of ubiquitous pyridine-fused N-heteroarenes is a practical method to synthesize structurally novel N-heterocycles, which is important for the development of medicines, bioactive agents, agrochemicals, materials, ligands, sensors, pigments, dyes, etc. However, owing to thermodynamic stability, kinetic inertness, and lone electron pair–induced catalyst deactivation of the pyridine-fused N-heteroarenes, limited strategies (e.g., C–H activation/functionalization, electrophilic substitution, and the Minisci reaction) are available to realize the synthetic purpose and maintain the aromaticity of the final products. Moreover, the relevant transformations have limitations such as needing harsh reaction conditions, requiring the preinstallation of specific coupling agents containing transformable functionalities or directing groups, using less environmentally benign oxidants and/or acidic activators, and poor selectivity. Herein, considering that imines, enamines, radicals, and cyclic amines are generated during the reduction of pyridine-fused N-heteroarenes, the precise transformation of these reductive intermediates offers a fundamental basis for developing novel tandem reactions. Our group revealed that a slow reduction rate, synergistic catalysis, and controlled electroreduction are effective strategies for fulfilling the selective reductive functionalization of pyridine-fused N-heteroarenes. Thus, we established a series of new synthetic methods that provide diverse construction modalities for functionalized N-heterocycles. The striking features of these synthetic methods include high efficiency, atom economy, and the use of readily accessible N-heteroarenes as transformable feedstocks in the absence of flammable and pressurized H2 gas, alongside a promising potential of the obtained N-heterocyclic products. The present study would be appealing to the fields of synthetic organic chemistry, catalysis, biomedical chemistry, and functional materials. This Account describes the application of reductive dearomatization as substrate-activating and tandem reaction-initiating modes and summarizes the reductive functionalization of pyridine-fused N-heteroarenes via selective alkylation, arylation, and annulation at nitrogen, α, β, and other remote carbon sites achieved over the past 8 years. Details regarding the development of new reactions and their plausible mechanisms and perspectives are discussed. We hope our contributions to this field will aid in the further development of novel strategies for the functionalization/transformation of pyridine-fused N-heteroarenes and tackle the intractable challenges in this area.
{"title":"Reductive Functionalization of Pyridine-Fused N-Heteroarenes","authors":"Huanhuan Jia, Zhenda Tan and Min Zhang*, ","doi":"10.1021/acs.accounts.4c00009","DOIUrl":"10.1021/acs.accounts.4c00009","url":null,"abstract":"<p >The selective functionalization/transformation of ubiquitous pyridine-fused N-heteroarenes is a practical method to synthesize structurally novel N-heterocycles, which is important for the development of medicines, bioactive agents, agrochemicals, materials, ligands, sensors, pigments, dyes, etc. However, owing to thermodynamic stability, kinetic inertness, and lone electron pair–induced catalyst deactivation of the pyridine-fused N-heteroarenes, limited strategies (e.g., C–H activation/functionalization, electrophilic substitution, and the Minisci reaction) are available to realize the synthetic purpose and maintain the aromaticity of the final products. Moreover, the relevant transformations have limitations such as needing harsh reaction conditions, requiring the preinstallation of specific coupling agents containing transformable functionalities or directing groups, using less environmentally benign oxidants and/or acidic activators, and poor selectivity. Herein, considering that imines, enamines, radicals, and cyclic amines are generated during the reduction of pyridine-fused N-heteroarenes, the precise transformation of these reductive intermediates offers a fundamental basis for developing novel tandem reactions. Our group revealed that a slow reduction rate, synergistic catalysis, and controlled electroreduction are effective strategies for fulfilling the selective reductive functionalization of pyridine-fused N-heteroarenes. Thus, we established a series of new synthetic methods that provide diverse construction modalities for functionalized N-heterocycles. The striking features of these synthetic methods include high efficiency, atom economy, and the use of readily accessible N-heteroarenes as transformable feedstocks in the absence of flammable and pressurized H<sub>2</sub> gas, alongside a promising potential of the obtained N-heterocyclic products. The present study would be appealing to the fields of synthetic organic chemistry, catalysis, biomedical chemistry, and functional materials. This Account describes the application of reductive dearomatization as substrate-activating and tandem reaction-initiating modes and summarizes the reductive functionalization of pyridine-fused N-heteroarenes via selective alkylation, arylation, and annulation at nitrogen, α, β, and other remote carbon sites achieved over the past 8 years. Details regarding the development of new reactions and their plausible mechanisms and perspectives are discussed. We hope our contributions to this field will aid in the further development of novel strategies for the functionalization/transformation of pyridine-fused N-heteroarenes and tackle the intractable challenges in this area.</p>","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":null,"pages":null},"PeriodicalIF":18.3,"publicationDate":"2024-02-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139939078","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-22DOI: 10.1021/acs.accounts.3c00760
Debasish Ghorai, Balázs L. Tóth, Matteo Lanzi and Arjan W. Kleij*,
Biologically active compounds and pharmaceutically relevant intermediates often feature sterically congested stereogenic centers, in particular, carbon stereocenters that are either tertiary tetrasubstituted ones or quaternary in nature. Synthons that comprise such bulky and often structurally complex core units are of high synthetic value and represent important incentives for communities connected to drug discovery and development. Streamlined approaches that give access to a diverse set of compounds incorporating acyclic bulky stereocenters are relatively limited, though vital. They enable further exploration of three-dimensional entities that can be designed and implemented in discovery programs, thereby extending the pool of molecular properties that is inaccessible for flat molecules. However, the lack of modular substrates in particular areas of chemical space inspired us to consider functionalized heterocycles known as cyclic carbonates and carbamates as a productive way to create sterically crowded alkenes and stereocenters.
In this Account, we describe the major approximations we followed over the course of 8 years using transition metal (TM) catalysis as an instrument to control the stereochemical course of various allylic and propargylic substitution processes and related transformations. Allylic substitution reactions empowered by Pd-catalysis utilizing a variety of nucleophiles are discussed, with amination being the seed of all of this combined work. These procedures build on vinyl-substituted cyclic carbonates (VCCs) that are simple and easy-to-access precursors and highly modular in nature compared to synthetically limited vinyl oxiranes. Overall these decarboxylative conversions take place with either “linear” or “branched” regioselectivities that are ligand controlled and offer access to a wide scope of functional allylic scaffolds. Alternative approaches, including dual TM/photocatalyzed transformations, allowed us to expand the repertoire of challenging stereoselective conversions. This was achieved through key single-electron pathways and via formal umpolung of intermediates, resulting in new types of carbon–carbon bond formation reactions significantly expanding the scope of allylic substitution reactions.
Heterocyclic substrate variants that have triple bond functional groups were also designed by us to enable difficult-to-promote stereoselective propargylic substitution reactions through TM catalysis. In these processes, inspired by the Nishibayashi laboratory and their seminal findings in the area, we discovered various new reactivity patterns. This provided access to a range of different stereodefined building blocks such as 1,2-diborylated 1,3-dienes and tetrasubstituted α-allenols under Cu- or Ni-catalysis. In this realm, the use of lactone-derived substrates gives access to elusive chiral γ-amino acids and lactams with high stereofidelity and good structural diversity.
{"title":"Vinyl and Alkynyl Substituted Heterocycles as Privileged Scaffolds in Transition Metal Promoted Stereoselective Synthesis","authors":"Debasish Ghorai, Balázs L. Tóth, Matteo Lanzi and Arjan W. Kleij*, ","doi":"10.1021/acs.accounts.3c00760","DOIUrl":"10.1021/acs.accounts.3c00760","url":null,"abstract":"<p >Biologically active compounds and pharmaceutically relevant intermediates often feature sterically congested stereogenic centers, in particular, carbon stereocenters that are either tertiary tetrasubstituted ones or quaternary in nature. Synthons that comprise such bulky and often structurally complex core units are of high synthetic value and represent important incentives for communities connected to drug discovery and development. Streamlined approaches that give access to a diverse set of compounds incorporating acyclic bulky stereocenters are relatively limited, though vital. They enable further exploration of three-dimensional entities that can be designed and implemented in discovery programs, thereby extending the pool of molecular properties that is inaccessible for flat molecules. However, the lack of modular substrates in particular areas of chemical space inspired us to consider functionalized heterocycles known as cyclic carbonates and carbamates as a productive way to create sterically crowded alkenes and stereocenters.</p><p >In this Account, we describe the major approximations we followed over the course of 8 years using transition metal (TM) catalysis as an instrument to control the stereochemical course of various allylic and propargylic substitution processes and related transformations. Allylic substitution reactions empowered by Pd-catalysis utilizing a variety of nucleophiles are discussed, with amination being the seed of all of this combined work. These procedures build on vinyl-substituted cyclic carbonates (VCCs) that are simple and easy-to-access precursors and highly modular in nature compared to synthetically limited vinyl oxiranes. Overall these decarboxylative conversions take place with either “linear” or “branched” regioselectivities that are ligand controlled and offer access to a wide scope of functional allylic scaffolds. Alternative approaches, including dual TM/photocatalyzed transformations, allowed us to expand the repertoire of challenging stereoselective conversions. This was achieved through key single-electron pathways and via formal umpolung of intermediates, resulting in new types of carbon–carbon bond formation reactions significantly expanding the scope of allylic substitution reactions.</p><p >Heterocyclic substrate variants that have triple bond functional groups were also designed by us to enable difficult-to-promote stereoselective propargylic substitution reactions through TM catalysis. In these processes, inspired by the Nishibayashi laboratory and their seminal findings in the area, we discovered various new reactivity patterns. This provided access to a range of different stereodefined building blocks such as 1,2-diborylated 1,3-dienes and tetrasubstituted α-allenols under Cu- or Ni-catalysis. In this realm, the use of lactone-derived substrates gives access to elusive chiral γ-amino acids and lactams with high stereofidelity and good structural diversity.</p><p >Apart from the syntheti","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":null,"pages":null},"PeriodicalIF":18.3,"publicationDate":"2024-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://pubs.acs.org/doi/epdf/10.1021/acs.accounts.3c00760","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139928887","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-22DOI: 10.1021/acs.accounts.3c00793
Kun Yang, Zuhao Li, Yulin Huang and Zebing Zeng*,
Polycyclic (hetero)aromatic hydrocarbons (PAHs) have emerged as a focal point in current interdisciplinary research, spanning the realms of chemistry, physics, and materials science. Possessing distinctive optical, electronic, and magnetic properties, these π-functional materials exhibit significant potential across diverse applications, including molecular electronic devices, organic spintronics, and biomedical functions, among others. Despite the extensive documentation of various PAHs over the decades, the efficient and precise synthesis of π-extended PAHs remains a formidable challenge, hindering their broader application. This challenge is primarily attributed to the intricate and often elusive nature of their synthesis, compounded by issues related to low solubility and unfavored stability.
The development of π-building blocks that can be facilely and modularly transformed into diverse π-frameworks constitutes a potent strategy for the creation of novel PAH materials. For instance, based on the classic perylene diimide (PDI) unit, researchers such as Würthner, Wang, and Nuckolls have successfully synthesized a plethora of structurally diverse PAHs, as well as numerous other π-functional materials. However, until now the availability of such versatile building blocks is still severely limited, especially for those simultaneously having a facile preparation process, adequate solubilizing groups, favored material stability, and critically, rich possibilities for structural extension spaces.
In this Account, we present an overview of our invention of a highly versatile bay-/ortho-octa-substituted perylene building block, designated as Per-4Br, for the construction of a series of novel PAH scaffolds with tailor-made structures and rich optoelectronic and magnetic properties. First, starting with a brief discussion of current challenges associated with the bottom-up synthesis of π-extended PAHs, we rationalize the key features of Per-4Br that enable facile access to new PAH molecules including its ease of large-scale preparation, favored material stability and solubility, and multiple flexible reaction sites, with a comparison to the PDI motif. Then, we showcase our rational design and sophisticated synthesis of a body of neutral or charged, closed- or open-shell, curved, or planar PAHs via controlled annulative π-extensions in different directions such as peripheral, diagonal, or multiple dimensions of the Per-4Br skeleton. In this part, the fundamental structure–property relationships between molecular conformations, electronic structures, and self-assembly behaviors of these PAHs and their unique physiochemical properties such as unusual open-shell ground states, global aromaticity, state-associated/stimuli-responsive magnetic activity, and charge transport characteristics will be emphatically elaborated. Finally, we offer our perspective on the continued advancement of π-functional material
{"title":"bay/ortho-Octa-substituted Perylene: A Versatile Building Block toward Novel Polycyclic (Hetero)Aromatic Hydrocarbons","authors":"Kun Yang, Zuhao Li, Yulin Huang and Zebing Zeng*, ","doi":"10.1021/acs.accounts.3c00793","DOIUrl":"10.1021/acs.accounts.3c00793","url":null,"abstract":"<p >Polycyclic (hetero)aromatic hydrocarbons (PAHs) have emerged as a focal point in current interdisciplinary research, spanning the realms of chemistry, physics, and materials science. Possessing distinctive optical, electronic, and magnetic properties, these π-functional materials exhibit significant potential across diverse applications, including molecular electronic devices, organic spintronics, and biomedical functions, among others. Despite the extensive documentation of various PAHs over the decades, the efficient and precise synthesis of π-extended PAHs remains a formidable challenge, hindering their broader application. This challenge is primarily attributed to the intricate and often elusive nature of their synthesis, compounded by issues related to low solubility and unfavored stability.</p><p >The development of π-building blocks that can be facilely and modularly transformed into diverse π-frameworks constitutes a potent strategy for the creation of novel PAH materials. For instance, based on the classic perylene diimide (PDI) unit, researchers such as Würthner, Wang, and Nuckolls have successfully synthesized a plethora of structurally diverse PAHs, as well as numerous other π-functional materials. However, until now the availability of such versatile building blocks is still severely limited, especially for those simultaneously having a facile preparation process, adequate solubilizing groups, favored material stability, and critically, rich possibilities for structural extension spaces.</p><p >In this Account, we present an overview of our invention of a highly versatile <i>bay</i>-/<i>ortho</i>-octa-substituted perylene building block, designated as <b>Per-4Br</b>, for the construction of a series of novel PAH scaffolds with tailor-made structures and rich optoelectronic and magnetic properties. First, starting with a brief discussion of current challenges associated with the bottom-up synthesis of π-extended PAHs, we rationalize the key features of <b>Per-4Br</b> that enable facile access to new PAH molecules including its ease of large-scale preparation, favored material stability and solubility, and multiple flexible reaction sites, with a comparison to the PDI motif. Then, we showcase our rational design and sophisticated synthesis of a body of neutral or charged, closed- or open-shell, curved, or planar PAHs via controlled annulative π-extensions in different directions such as peripheral, diagonal, or multiple dimensions of the <b>Per-4Br</b> skeleton. In this part, the fundamental structure–property relationships between molecular conformations, electronic structures, and self-assembly behaviors of these PAHs and their unique physiochemical properties such as unusual open-shell ground states, global aromaticity, state-associated/stimuli-responsive magnetic activity, and charge transport characteristics will be emphatically elaborated. Finally, we offer our perspective on the continued advancement of π-functional material","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":null,"pages":null},"PeriodicalIF":18.3,"publicationDate":"2024-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139927175","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-21DOI: 10.1021/acs.accounts.3c00804
Wei Wen, and , Qi-Xiang Guo*,
The development of catalytic activation modes provides a reliable and effective platform for designing new enantioselective reactions and preparing chiral molecules with diverse structures. Chiral aldehyde catalysis is an attractive concept in asymmetric catalysis, which utilizes a chiral aldehyde catalyst to promote the asymmetric hydroamination of allylic amines, the asymmetric α-functionalization of primary amines, or the asymmetric transamination of α-keto esters. Typically, the chiral aldehyde-catalyzed asymmetric α-functionalization of primary amines provides an efficient and straightforward method for the synthesis of α-functionalized chiral amines, which does not require any additional protection or deprotection manipulations of the amine group. However, achieving catalytic stereoselective transformations with high efficiency and enantioselectivity by this strategy has remained an intractable challenge.
This Account summarizes our endeavors in the development and application of chiral aldehyde catalysis. Using a chiral aldehyde as a catalyst, we reported the catalytic asymmetric α-C alkylation of 2-aminomalonate with 3-indolylmethanol in 2014, which represents the first chiral aldehyde-catalyzed asymmetric α-functionalization of an activated primary amine. Subsequently, several axially chiral aldehyde catalysts were continuously prepared by using chiral BINOL as the starting material, and their applications in asymmetric synthesis were explored. On the one hand, they were used as organocatalysts to realize the various transformations of α-amino acid esters, such as asymmetric 1,4-addition toward conjugated enones/α,β-unsaturated diesters and cyclic 1-azadienes as well as asymmetric α-arylation/allylation and benzylation with corresponding halohydrocarbons. Notably, taking advantage of the difference in the distribution of catalytic sites between two chiral aldehyde catalysts, we disclosed chiral aldehyde-catalyzed diastereodivergent 1,6-conjugated addition and Mannich reactions. On the other hand, the potential for the cooperative catalysis of a chiral aldehyde with a transition metal has also been demonstrated. Enabled by the combination of a chiral aldehyde, a palladium complex, and a Lewis acid, the enantioselective α-allylation of amino acid esters with allyl alcohol esters was established. Moreover, the ternary catalytic system has been successfully used for the α-functionalization of amino acid esters with 1,3-dienes, allenes, allenylic alcohol esters, 1,3-disubstituted allyl alcohol esters, and arylmethanol esters as well as the asymmetric cascade Heck-alkylation reaction. The combination of a chiral aldehyde and nickel complex allows for the asymmetric α-propargylation of amino acid esters with propargylic alcohol esters and provides excellent enantioselectivities. These transformations provide a large library of optically active amines and amino acids. With those chiral amino acid esters as key building blocks, the syn
{"title":"Chiral Aldehyde Catalysis-Enabled Asymmetric α-Functionalization of Activated Primary Amines","authors":"Wei Wen, and , Qi-Xiang Guo*, ","doi":"10.1021/acs.accounts.3c00804","DOIUrl":"10.1021/acs.accounts.3c00804","url":null,"abstract":"<p >The development of catalytic activation modes provides a reliable and effective platform for designing new enantioselective reactions and preparing chiral molecules with diverse structures. Chiral aldehyde catalysis is an attractive concept in asymmetric catalysis, which utilizes a chiral aldehyde catalyst to promote the asymmetric hydroamination of allylic amines, the asymmetric α-functionalization of primary amines, or the asymmetric transamination of α-keto esters. Typically, the chiral aldehyde-catalyzed asymmetric α-functionalization of primary amines provides an efficient and straightforward method for the synthesis of α-functionalized chiral amines, which does not require any additional protection or deprotection manipulations of the amine group. However, achieving catalytic stereoselective transformations with high efficiency and enantioselectivity by this strategy has remained an intractable challenge.</p><p >This Account summarizes our endeavors in the development and application of chiral aldehyde catalysis. Using a chiral aldehyde as a catalyst, we reported the catalytic asymmetric α-C alkylation of 2-aminomalonate with 3-indolylmethanol in 2014, which represents the first chiral aldehyde-catalyzed asymmetric α-functionalization of an activated primary amine. Subsequently, several axially chiral aldehyde catalysts were continuously prepared by using chiral BINOL as the starting material, and their applications in asymmetric synthesis were explored. On the one hand, they were used as organocatalysts to realize the various transformations of α-amino acid esters, such as asymmetric 1,4-addition toward conjugated enones/α,β-unsaturated diesters and cyclic 1-azadienes as well as asymmetric α-arylation/allylation and benzylation with corresponding halohydrocarbons. Notably, taking advantage of the difference in the distribution of catalytic sites between two chiral aldehyde catalysts, we disclosed chiral aldehyde-catalyzed diastereodivergent 1,6-conjugated addition and Mannich reactions. On the other hand, the potential for the cooperative catalysis of a chiral aldehyde with a transition metal has also been demonstrated. Enabled by the combination of a chiral aldehyde, a palladium complex, and a Lewis acid, the enantioselective α-allylation of amino acid esters with allyl alcohol esters was established. Moreover, the ternary catalytic system has been successfully used for the α-functionalization of amino acid esters with 1,3-dienes, allenes, allenylic alcohol esters, 1,3-disubstituted allyl alcohol esters, and arylmethanol esters as well as the asymmetric cascade Heck-alkylation reaction. The combination of a chiral aldehyde and nickel complex allows for the asymmetric α-propargylation of amino acid esters with propargylic alcohol esters and provides excellent enantioselectivities. These transformations provide a large library of optically active amines and amino acids. With those chiral amino acid esters as key building blocks, the syn","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":null,"pages":null},"PeriodicalIF":18.3,"publicationDate":"2024-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139916062","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-19DOI: 10.1021/acs.accounts.3c00777
Xue Dong, Hang Qu, Andrew C.-H. Sue, Xin-Chang Wang* and Xiao-Yu Cao*,
Molecular polyhedral cages, notable for their enclosed inner cavities, can possess varying degrees of symmetry, spanning from regular Platonic polyhedra to lower symmetry forms that may display chirality. Crafting chiral molecular cages typically involves using building blocks containing stereogenic elements or arranging achiral components in a manner that lacks mirror and inversion symmetries. Achieving precise control over their chirality poses both significance and challenges.
In this Account, we present an overview of our research endeavors in the realm of chiral molecular polyhedral cages, drawing inspiration from Buckminster Fuller’s “Face-Rotating Polyhedra (FRP)”. Mathematically, FRP introduce a unique form of chirality distinguished by a rotating pattern around the center of each face, setting it apart from regular polyhedra.
Molecular FRP can be constructed using two types of facial building blocks. The first includes rigid, planar molecules such as truxene and triazatruxene, which exhibit either clockwise or counterclockwise rotations in two dimensions. The second category involves propeller-like molecules, e.g., tetraphenylethylene, 1,2,3,4,5-penta(4-phenylaldehyde)pyrrole, and tridurylborane, displaying dynamic stereochemistry.
The synthesis of FRP may potentially yield a diverse array of stereoisomers. Achieving high stereoselectivity becomes feasible through the selection of building blocks with specific substitution patterns and rigidity. Prominent noncovalent repulsive forces within the resulting cages often play a pivotal role in the dynamic covalent assembly process, ultimately leading to the formation of thermodynamically stable FRP products.
The capacity to generate a multitude of stereoisomers, combined with the integration of chiral vertices, has facilitated investigations into phenomena such as chiral self-sorting and the “sergeant and soldiers” chiral amplification effect in FRP. Even the inclusion of one chiral vertex significantly impacts the stereochemical configuration of the entire cage. While many facial building blocks establish a stable rotational pattern in FRP, other units, such as tridurylborane, can dynamically transition between P and M configurations within the cage structures. The kinetic characteristics of such stereolabile FRP can be elucidated through physicochemical investigations.
Our research extends beyond the FRP concept to encompass mathematical analysis of these structures. Graph theory, particularly the coloring problem, sheds light on the intricate facial patterns exhibited by various FRP stereoisomers and serves as an efficient tool to facilitate the discovery of novel FRP structures. This approach offers a fresh paradigm for designing and analyzing chiral molecular polyhedral cages, showcasing in our work the synergy between mathematics and molecular design.
{"title":"Molecular Face-Rotating Polyhedra: Chiral Cages Inspired by Mathematics","authors":"Xue Dong, Hang Qu, Andrew C.-H. Sue, Xin-Chang Wang* and Xiao-Yu Cao*, ","doi":"10.1021/acs.accounts.3c00777","DOIUrl":"10.1021/acs.accounts.3c00777","url":null,"abstract":"<p >Molecular polyhedral cages, notable for their enclosed inner cavities, can possess varying degrees of symmetry, spanning from regular Platonic polyhedra to lower symmetry forms that may display chirality. Crafting chiral molecular cages typically involves using building blocks containing stereogenic elements or arranging achiral components in a manner that lacks mirror and inversion symmetries. Achieving precise control over their chirality poses both significance and challenges.</p><p >In this Account, we present an overview of our research endeavors in the realm of chiral molecular polyhedral cages, drawing inspiration from Buckminster Fuller’s “Face-Rotating Polyhedra (FRP)”. Mathematically, FRP introduce a unique form of chirality distinguished by a rotating pattern around the center of each face, setting it apart from regular polyhedra.</p><p >Molecular FRP can be constructed using two types of facial building blocks. The first includes rigid, planar molecules such as truxene and triazatruxene, which exhibit either clockwise or counterclockwise rotations in two dimensions. The second category involves propeller-like molecules, e.g., tetraphenylethylene, 1,2,3,4,5-penta(4-phenylaldehyde)pyrrole, and tridurylborane, displaying dynamic stereochemistry.</p><p >The synthesis of FRP may potentially yield a diverse array of stereoisomers. Achieving high stereoselectivity becomes feasible through the selection of building blocks with specific substitution patterns and rigidity. Prominent noncovalent repulsive forces within the resulting cages often play a pivotal role in the dynamic covalent assembly process, ultimately leading to the formation of thermodynamically stable FRP products.</p><p >The capacity to generate a multitude of stereoisomers, combined with the integration of chiral vertices, has facilitated investigations into phenomena such as chiral self-sorting and the “sergeant and soldiers” chiral amplification effect in FRP. Even the inclusion of one chiral vertex significantly impacts the stereochemical configuration of the entire cage. While many facial building blocks establish a stable rotational pattern in FRP, other units, such as tridurylborane, can dynamically transition between <i>P</i> and <i>M</i> configurations within the cage structures. The kinetic characteristics of such stereolabile FRP can be elucidated through physicochemical investigations.</p><p >Our research extends beyond the FRP concept to encompass mathematical analysis of these structures. Graph theory, particularly the coloring problem, sheds light on the intricate facial patterns exhibited by various FRP stereoisomers and serves as an efficient tool to facilitate the discovery of novel FRP structures. This approach offers a fresh paradigm for designing and analyzing chiral molecular polyhedral cages, showcasing in our work the synergy between mathematics and molecular design.</p>","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":null,"pages":null},"PeriodicalIF":18.3,"publicationDate":"2024-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139898881","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}