共查询到20条相似文献,搜索用时 15 毫秒
1.
Dr. Kerstin Freitag Dr. Christian Gemel Dr. Paul Jerabek Prof. Dr. Iris M. Oppel Dr. Rüdiger W. Seidel Prof. Dr. Gernot Frenking Hung Banh Katharina Dilchert Prof. Dr. Roland A. Fischer 《Angewandte Chemie (International ed. in English)》2015,54(14):4370-4374
The triangular clusters [Zn3Cp*3]+ and [Zn2CuCp*3] were obtained by addition of the in situ generated, electrophilic, and isolobal species [ZnCp*]+ and [CuCp*] to Carmona’s compound, [Cp*Zn? ZnCp*], without splitting the Zn? Zn bond. The choice of non‐coordinating fluoroaromatic solvents was crucial. The bonding situations of the all‐hydrocarbon‐ligand‐protected clusters were investigated by quantum chemical calculations revealing a high degree of σ‐aromaticity similar to the triatomic hydrogen ion [H3]+. The new species serve as molecular building units of CunZnm nanobrass clusters as indicated by LIFDI mass spectrometry. 相似文献
2.
3.
Understanding the Fundamental Role of π/π, σ/σ, and σ/π Dispersion Interactions in Shaping Carbon‐Based Materials 下载免费PDF全文
Dr. Mercedes Alonso Tatiana Woller Dr. Francisco J. Martín‐Martínez Dr. Julia Contreras‐García Prof. Paul Geerlings Prof. Frank De Proft 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(17):4931-4941
Noncovalent interactions involving aromatic rings, such as π‐stacking and CH/π interactions, are central to many areas of modern chemistry. However, recent studies proved that aromaticity is not required for stacking interactions, since similar interaction energies were computed for several aromatic and aliphatic dimers. Herein, the nature and origin of π/π, σ/σ, and σ/π dispersion interactions has been investigated by using dispersion‐corrected density functional theory, energy decomposition analysis, and the recently developed noncovalent interaction (NCI) method. Our analysis shows that π/π and σ/σ stacking interactions are equally important for the benzene and cyclohexane dimers, explaining why both compounds have similar boiling points. Also, similar dispersion forces are found in the benzene???methane and cyclohexane???methane complexes. However, for systems larger than naphthalene, there are enhanced stacking interactions in the aromatic dimers adopting a parallel‐displaced configuration compared to the analogous saturated systems. Although dispersion plays a decisive role in stabilizing all the complexes, the origin of the π/π, σ/σ, and σ/π interactions is different. The NCI method reveals that the dispersion interactions between the hydrogen atoms are responsible for the surprisingly strong aliphatic interactions. Moreover, whereas σ/σ and σ/π interactions are local, the π/π stacking are inherently delocalized, which give rise to a non‐additive effect. These new types of dispersion interactions between saturated groups can be exploited in the rational design of novel carbon materials. 相似文献
4.
Cover Picture: Understanding the Fundamental Role of π/π, σ/σ, and σ/π Dispersion Interactions in Shaping Carbon‐Based Materials (Chem. Eur. J. 17/2014) 下载免费PDF全文
Dr. Mercedes Alonso Tatiana Woller Dr. Francisco J. Martín‐Martínez Dr. Julia Contreras‐García Prof. Paul Geerlings Prof. Frank De Proft 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(17):4841-4841
5.
D6h‐Au42 Isomer: A Golden Aromatic Toroid Involving Superatomic π‐Orbitals that Follow the Hückel (4n+2)π rule 下载免费PDF全文
Dr. Alvaro Muñoz‐Castro 《Chemphyschem》2016,17(20):3204-3208
Recently, it has been shown that the superatom concept is intimately connected to relevant tools of great chemical significance, such as the Lewis structure model and the VSEPR theory, which has been employed to understand hybridized and dimeric‐like molecules. This suggests a potential rational construction of superatomic clusters mimicking more complex structures. Here, we extend another well‐employed concept to the superatomic clusters, to construct a novel Au42 isomer with resemblance to cyclic aromatic molecules. It is shown that the Hückel (4n+2)π rule is ready to be applied, predicting aromatic behavior latterly supported by the favorable evaluation of the induced shielding cone formation. The D6h isomer of Au42 described here exhibits inherent characteristics mimicking aromatic hydrocarbon rings, displaying π‐superatomic orbitals and related properties. This new cluster is the first member of the superatomic clusters family to exhibit an aromatic π‐electron system. 相似文献
6.
Nature of Bonding in Bowl‐Like B36 Cluster Revisited: Concentric (6π+18π) Double Aromaticity and Reason for the Preference of a Hexagonal Hole in a Central Location 下载免费PDF全文
The bowl‐shaped C6v B36 cluster with a central hexagon hole is considered an ideal molecular model for low‐dimensional boron‐based nanosystems. Owing to the electron deficiency of boron, chemical bonding in the B36 cluster is intriguing, complicated, and has remained elusive despite a couple of papers in the literature. Herein, a bonding analysis is given through canonical molecular orbitals (CMOs) and adaptive natural density partitioning (AdNDP), further aided by natural bond orbital (NBO) analysis and orbital composition calculations. The concerted computational data establish the idea of concentric double π aromaticity for the B36 cluster, with inner 6π and outer 18π electron counting, which both conform to the (4n+2) Hückel rule. The updated bonding picture differs from existing knowledge of the system. A refined bonding model is also proposed for coronene, of which the B36 cluster is an inorganic analogue. It is further shown that concentric double π aromaticity in the B36 cluster is retained and spatially fixed, irrespective of the migration of the hexagonal hole; the latter process changes the system energetically. The hexagonal hole is a destabilizing factor for σ/π CMOs. The central hexagon hole affects substantially fewer CMOs, thus making the bowl‐shaped C6v B36 cluster the global minimum. 相似文献
7.
8.
Bartosz Szyszko Dr. Natasza Sprutta Dr. Paulina Chwalisz Dr. Marcin Stępień Prof. Lechosław Latos‐Grażyński 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(7):1985-1997
The four expanded p‐benziporphyrins A,C‐di‐p‐benzi[24]pentaphyrin(1.1.1.1.1), N‐fused A‐p‐benzi[24]pentaphyrin, A,D ‐di‐p‐benzi[28]hexaphyrin(1.1.1.1.1.1), and A,C‐di‐p‐benzi[28]hexaphyrin(1.1.1.1.1.1) were obtained in three‐component Lindsey‐type macrocyclizations. These compounds were explored as macrocyclic ligands and as potential aromaticity switches. A BODIPY‐like difluoroboron complex was obtained from the A,C‐di‐p‐benzi[24]pentaphyrin, whereas A,C‐di‐p‐benzi[28]hexaphyrin yielded a Möbius‐aromatic PdII complex containing fused pyrrole and phenylene subunits. Conformational behavior, tautomerism, and acid‐base chemistry of the new macrocycles were characterized by means of NMR spectroscopy and DFT calculations. Free base N‐fused A‐p‐benzi[24]pentaphyrin showed temperature‐dependent Hückel–Möbius aromaticity switching, whereas the A,C‐di‐p‐benzi[28]hexaphyrin formed a Möbius‐aromatic dication. 相似文献
9.
Alexander Hofmann Marc‐Andr Lgar Leonie Wüst Holger Braunschweig 《Angewandte Chemie (International ed. in English)》2019,58(29):9776-9781
Heterodiatomic multiple bonds have never been observed within Group 13. Herein, we disclose a method that generates [(CAAC)PhB=AlCp3t] ( 1 ), a complex featuring π bonding between boron and aluminum through the association of singlet fragments. We present the properties of this multiple bond as well as the reactivity of the complex with carbon dioxide, which yields a boron CO complex via an unusual metathesis reaction. 相似文献
10.
σ Aromaticity Dominates in the Unsaturated Three‐Membered Ring of Cyclopropametallapentalenes from Groups 7–9: A DFT Study 下载免费PDF全文
Yulei Hao Jingjing Wu Prof. Dr. Jun Zhu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(51):18805-18810
Aromaticity, an old but still fantastic topic, has long attracted considerable interest of chemists. Generally, π aromaticity is described by π‐electron delocalization in closed circuits of unsaturated compounds whereas σ‐electron delocalization in saturated rings leads to σ aromaticity. Interestingly, our recent study shows that σ aromaticity can be dominating in an unsaturated three‐membered ring (3MR) of cyclopropaosmapentalene. An interesting question is raised: Can the σ aromaticity, which is dominant in the unsaturated 3MR, be extended to other cyclopropametallapentalenes? If so, how could the metal centers, ligands, and substituents affect the σ aromaticity? Here, we report a thorough theoretical study on these issues. The nucleus‐independent chemical shift calculations and the anisotropy of the current‐induced density plots reveal the dominant σ aromaticity in these unsaturated 3MRs. In addition, our calculations show that substituents on the 3MRs have significant effects on the σ aromaticity, whereas the ligand effect is particularly small. 相似文献
11.
Observation of a Thermally Accessible Triplet State Resulting from Rotation around a Main‐Group π Bond 下载免费PDF全文
Arseni Kostenko Dr. Boris Tumanskii Dr. Miriam Karni Prof. Shigeyoshi Inoue Prof. Masaaki Ichinohe Prof. Akira Sekiguchi Prof. Yitzhak Apeloig 《Angewandte Chemie (International ed. in English)》2015,54(41):12144-12148
We report the first direct spectroscopic observation by electron paramagnetic resonance (EPR) spectroscopy of a triplet diradical that is formed in a thermally induced rotation around a main‐group π bond, that is, the Si?Si double bond of tetrakis(di‐tert‐butylmethylsilyl)disilene ( 1 ). The highly twisted ground‐state geometry of singlet 1 allows access to the perpendicular triplet diradical 2 at moderate temperatures of 350–410 K. DFT‐calculated zero‐field splitting (ZFS) parameters of 2 accurately reproduce the experimentally observed half‐field transition. Experiment and theory suggest a thermal equilibrium between 1 and 2 with a very low singlet–triplet energy gap of only 7.3 kcal mol?1. 相似文献
12.
Curt Wentrup 《Angewandte Chemie (International ed. in English)》2020,59(22):8332-8342
Zeise's salt, KPt(C2H4)Cl3, was the first characterized organometallic compound; it was also the first olefin π‐complex. It was published in 1825–1830 in the middle of a fight between Dumas on the one hand and Berzelius and Liebig on the other, who defended the etherin (ethylene) and radical theories, respectively. Although Zeise's formulation as a compound containing ethylene was vindicated, the fight went on for many years. This was a time when the theories of organic chemistry were being developed, before any clear understanding of the nature of molecules, bonding, and structure. Zeise thought of the structure of his salt as a product of the addition of PtCl2 to ethylene. Jensen assumed a central bonding to ethylene but needed theoretical assistance to explain it. His attempt to obtain such an explanation from Hückel failed, and it was Dewar who explained the nature of π‐complexes in molecular orbital terms in 1951. 相似文献
13.
The π contribution to the electron localization function (ELF) is used to compare 4nπ‐ and (4n+2)π‐electron annulenes, with particular focus on the aromaticity of 4nπ‐electron annulenes in their lowest triplet state. The analysis is performed on the electron density obtained at the level of OLYP density functional theory, as well as at the CCSD and CASSCF ab initio levels. Two criteria for aromaticity of all‐carbon annulenes are set up: the span in the bifurcation values ΔBV(ELFπ) should be small, ideally zero, and the bifurcation value for ring closure of the π basin RCBV(ELFπ) should be high (≥ 0.7). On the basis of these criteria, nearly all 4nπ‐electron annulenes are aromatic in their lowest triplet states, similar to (4n+2)π‐electron annulenes in their singlet ground states. For singlet biradical cyclobutadiene and cyclooctatetraene constrained to D4h and D8h symmetry, respectively, the RCBV(ELFπ) at the CASSCF level is lower (0.531 and 0.745) than for benzene (0.853), even though they have equal proportions of α‐ and β‐electrons. 相似文献
14.
Dr. Gang Zhang Dr. Frank Rominger Prof. Dr. Michael Mastalerz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(9):3084-3093
On the basis of a threefold borylated truxene, which is accessible in high yields by iridium‐catalyzed borylation under CH‐activation, fused π‐extended truxenes have been synthesized by a two‐step method of first Suzuki–Miyaura cross‐coupling reaction and subsequent condensation reaction. The mild condensation method tolerates the presence of a variety of functional groups, such as nitro, fluoro, or carboxyl moieties. Furthermore, by using this approach, N‐ and S‐heteroarene analogues become accessible for the first time, as well as larger structures that represent derivatives of precursors for fullerene C60 or buckybowls. The attached tert‐butyl groups make all derivatives sufficiently soluble to allow full spectroscopic and electrochemical investigations. Postfunctionalization of selected derivatives for further synthetic applications of the compounds is also presented. 相似文献
15.
Quinoidal/Aromatic Transformations in π‐Conjugated Oligomers: Vibrational Raman studies on the Limits of Rupture for π‐Bonds 下载免费PDF全文
《Angewandte Chemie (International ed. in English)》2017,56(9):2250-2259
The vibrational Raman spectra of several series of aromatic and quinoidal compounds have been analyzed considering the downshifts and upshifts of the frequencies of the relevant Raman bands as a function of the number of repeating units. Oligothiophenes, oligophenylene‐vinylenes, and oligoperylenes (oligophenyls) derivatives are studied in a common context. These shifts are taken as spectroscopic fingerprints of the changes in π‐conjugation. For a given family, aromatic and quinoidal oligomers have been studied together, and according to their Raman frequency shifts located in the two‐well BLA–energy curve of their ground electronic state as a function of the bond‐length‐alternation pattern (BLA). The connection among BLA values, π‐conjugation, and Raman frequencies is taken here as the basis of the study. These Raman shifts/BLA changes have been related to important electronic properties of these one‐dimensional linear π‐electron delocalized systems such as quinoidal (polyene) and aromatic characters. 相似文献
16.
17.
Jiaye Jin Prof. Guanjun Wang Prof. Mingfei Zhou Dr. Diego M. Andrada Dr. Markus Hermann Prof. Gernot Frenking 《Angewandte Chemie (International ed. in English)》2016,55(6):2078-2082
We report the spectroscopic identification of the [B3(NN)3]+ and [B3(CO)3]+ complexes, which feature the smallest π‐aromatic system B3+. A quantum chemical bonding analysis shows that the adducts are mainly stabilized by L→[B3L2]+ σ‐donation. 相似文献
18.
19.
σ‐Aromaticity in an Unsaturated Ring: Osmapentalene Derivatives Containing a Metallacyclopropene Unit 下载免费PDF全文
Dr. Congqing Zhu Xiaoxi Zhou Hongjie Xing Ke An Dr. Jun Zhu Prof. Dr. Haiping Xia 《Angewandte Chemie (International ed. in English)》2015,54(10):3102-3106
In general, aromaticity can be clarified as π‐ and σ‐aromaticity according to the type of electrons with major contributions. The traditional π‐aromaticity generally describes the π‐conjugation in fully unsaturated rings whereas σ‐aromaticity may stabilize fully saturated rings with delocalization caused by σ‐electron conjugation. Reported herein is an example of σ‐aromaticity in an unsaturated three‐membered ring (3 MR), which is supported by experimental observations and theoretical calculations. Specifically, when the 3 MR in cyclopropaosmapentalene is cleaved by ethane through two isodesmic reactions, both of them are highly endothermic (+29.7 and +35.0 kcal mol?1). These positive values are in sharp contrast to the expected exothermicity, thus indicating aromaticity in the 3 MR. Further nucleus‐independent chemical shift and anisotropy of the current‐induced density calculations reveal the nature of σ‐aromaticity in the unsaturated 3 MR. 相似文献
20.
Unexpected 1,2‐Migration in Metallasilabenzenes: Theoretical Evidence for Reluctance of Silicon to Participate in π Bonding 下载免费PDF全文
Density functional theory (DFT) calculations were carried out to investigate the 1,2‐migration in metallasilabenzenes. The results suggested that the chloride migration of metallabenzenes is unfavorable due to the loss of aromaticity in the nonaromatic analogues. In sharp contrast, such a migration in metallasilabenzenes is favorable due to the reluctance of silicon to participate in π bonding. The migration of hydride and methyl group from the metal center to the silicon atom in metallasilabenzenes is computed to be also feasible. In addition, the π donor ligand and the third row transition metal can stabilize metallasilabenzenes. Thus, such a migration becomes less favorable thermodynamically and kinetically. These findings could be very helpful for synthetic chemists to realize the first metallasilabenzene. 相似文献