News from Silicon: An Isomer of Hexasilabenzene and A Metal–Silicon Triple Bond

Gerdes, Claudia; Müller, Thomas

doi:10.1002/anie.201001558

Cited by 35 publications

(9 citation statements)

References 34 publications

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“…I never succeeded in making it, and indeed it has still only been discussed theoretically. [20] It is predicted to show none of the special stability of benzene, and should distort to non-planar structures. My efforts were unsuccessful, but they did get me a position as a finalist in the Westinghouse science contest for high school students.…”

Section: Aromaticitymentioning

confidence: 99%

“…When I read about the special property of benzene called aromaticity I decided to see whether the analog of benzene with silicon atoms in place of carbon, hexasilabenzene 7 , would also be aromatic. I never succeeded in making it, and indeed it has still only been discussed theoretically . It is predicted to show none of the special stability of benzene, and should distort to non‐planar structures.…”

Section: Nozoe and Isnamentioning

confidence: 99%

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Novel Aromatic and Antiaromatic Systems

Breslow

2014

The Chemical Record

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Note from the Editor: August Kekulé's dream and his theory of the structure of benzene (1865). Julius Thomsen's logic that benzene contains equivalent electrons between its carbon atoms (ca. 1900). Richard Willstätter's synthesis and observation that 1,3,5,7‐cyclooctatetraene is not aromatic (early 1900s). Sir Robert Robinson's proposal of the ‘aromatic sextet’ (1925). Erich Hückel's molecular orbital treatment of benzene and other unsaturated compounds that separated sigma and pi electrons (early 1930s). Tetsuo Nozoe and Michael Dewar's independent proposal of a new aromatic structure for a cycloheptatrieneone (mid‐1940s). Ronald Breslow's demonstration that cyclopropenyl cation is aromatic (1958). Breslow's proposal of ‘antiaromaticity’ (1965). I offer several comments. First, in the field of aromaticity, Breslow is in mighty exceptional company. Second, his research has extended well beyond aromaticity. Yes, Breslow is applying the concepts of antiaromaticity toward the development of highly conductive organic materials. But his research has encompassed enzyme mimics, remote functionalization reactions, unnatural DNA analogues and cancer chemotherapy. Indeed, Breslow is the co‐discoverer of a highly successful drug, Vorinostat, which is FDA‐approved for the treatment of cutaneous T‐cell lymphoma. We thank Professor Breslow for joining our project honoring his and our friend, Tetsuo Nozoe. Tetsuo Nozoe would have would have been deeply touched. —Jeffrey I. Seeman Guest Editor University of Richmond Richmond, Virginia 23173, USA E‐mail: jseeman@richmond.edu Ronald Breslow with Koji Nakanishi (left) and Tetsuo Nozoe (center), Sendai, 1970. Abstract We contributed to the field of non‐benzenoid aromatic compounds by creating the cyclopropenyl cation and various of its derivatives, including cyclopropenone; it was the first aromatic system with other than six pi electrons in a single ring, and the simplest aromatic system. The pioneering work of Tetsuo Nozoe in tropolone chemistry was celebrated with the founding of ISNA, the International Symposium on Non‐Benzenoid Aromatic Compounds, where I described our work in the field. It fit the prediction that aromaticity would be found in systems with 4n + 2 pi electrons, where n is an integer. I was also concerned with the properties of monocyclic systems with 4n cyclically conjugated pi electrons. They were expected not to be aromatic, but the interesting question was whether they were actually antiaromatic, especially destabilized by the cyclic conjugation in such 4n species as the cyclopropenyl anion, cyclobutadiene, and cyclopentadienyl cation. The evidence supports antiaromaticity in these cases. We also examined compounds where 4n cyclic pi systems were fused with aromatic systems, and most interestingly systems in which two 4n pi systems were fused. In these cases the periphery of the molecules had 4n + 2 pi electrons, for aromaticity, but the components were antiaromatic. Recently we have studied electrical conductivities in aromatic molecules such as thiophe...

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Section: Aromaticitymentioning

confidence: 99%

Section: Nozoe and Isnamentioning

confidence: 99%

Novel Aromatic and Antiaromatic Systems

Breslow

2014

The Chemical Record

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“…Benzene is a typical aromatic compound and is probably one of the most popular organic compounds . Therefore, its silicon analogues, silabenzenes in which all or a part of the skeletal carbon atoms of benzene are replaced with silicon atoms, have also been extensively investigated experimentally and theoretically in comparison with benzene for years. − Especially, there have been a large number of studies of the mono- and disilabenzenes and they have already been synthesized experimentally. − On the other hand, the structure and reactivity of larger sila-aromatic compounds consisting of tri- or tetrasilabenzene units have also been revealed by using quantum chemical calculations …”

Section: Introductionmentioning

confidence: 99%

Theoretical Study of the Si/C Mixed Benzenes and Their Major Valence Isomers

2020

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Changes in the structures and relative stabilities of benzene and the major valence isomers fulvene, Dewar benzene, benzvalene, and prismane on the substitution of the skeletal carbons with silicon atoms in a stepwise manner have been systematically investigated by ab initio molecular orbital methods. The number and arrangement of the formal CC, CSi and SiSi double bonds were found to be considerably important factors controlling the structure and relative stability of a series of the compounds for fulvene, Dewar benzene, and benzvalene analogues. Also, the applicability of “π-electron-holding ability” proposed for the planarity of heavy ethenes or polyenes in our previous study to the benzene analogues was confirmed. On the other hand, the angle strain is the key for the properties of prismane analogues, as expected. The noteworthy point is that benzene-type compounds tend to have a planar structure in comparison to fulvene analogues with a partially conjugated structure, and the stability relative to the other isomers is not extremely lowered even though the skeletal silicon atoms increase. Among them, the Si/C alternately mixed benzene (1,3,5-trisilabenzene) is an attractive “intermediate compound” between benzene and hexasilabenzene, as it has a planar and electronic structure similar to those of benzene. Therefore, in order to provide some useful information for its synthesis and isolation, the thermodynamic and kinetic stabilities were investigated. As a result, the Si/C alternately mixed benzene was found to be highly reactive for addition reactions, especially for a dimerization. However, as a cure for that, some promising cross-linking substituents considerably effective at preventing isomerization and dimerization were finally proposed.

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“…Benzene is one of the most famous organic compounds, as the archetypal compound with special stability (aromaticity). − Therefore, it is not surprising that a great deal of interest has been focused on the properties of analogous compounds of the heavier group-14 elements such as the all-silicon congener, hexasilabenzene (H 6 Si 6 ). − In spite of huge experimental efforts in silicon chemistry, the hexasilabenzene derivative has not been synthesized. According to previous theoretical studies, its molecular framework is nonplanar and chairlike with D 3 d symmetry, which is in sharp contrast to benzene.…”

Section: Introductionmentioning

confidence: 99%

Ab Initio Molecular Orbital Study of the First Four Si/C Alternately Substituted Annulenes

2019

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The ground and low-lying excited states of four alternating Si/C annulenes, H n Si n/2C n/2 with n = 4, 6, 8, and 10, have been investigated by ab initio molecular orbital methods and compared to those of their all-carbon and all-silicon analogues. In the ground state, all of the Si/C-mixed annulenes, except for the largest 10-membered annulene (H10Si5C5), assume equal-bond-length structures by adopting a closed-shell electronic structure in the possible highest symmetry. For the largest H10Si5C5, the trend of the bond delocalization still remains but the circular structure is considerably distorted and nonplanar due to severe angle strain. In the low-lying singlet (S1) and triplet (T1) states, the geometry of the compounds tends to be nonplanar as the excitations produce silyl radical character. Relative energies of the T1 and S1 states of the 6-membered ring, compared to those of the respective ground states (S0), are higher than those of the 4- and 8-membered rings, suggesting a special stability for H6Si3C3. The planar rhombus shape of the formally antiaromatic H4Si2C2 suggests that a synthetic effort is merited. Bonding analyses are given to support the conclusions reached on the basis of geometric structures and excited-state energetics.

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News from Silicon: An Isomer of Hexasilabenzene and A Metal–Silicon Triple Bond

Cited by 35 publications

References 34 publications

Novel Aromatic and Antiaromatic Systems

Novel Aromatic and Antiaromatic Systems

Theoretical Study of the Si/C Mixed Benzenes and Their Major Valence Isomers

Ab Initio Molecular Orbital Study of the First Four Si/C Alternately Substituted Annulenes

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