(π+σ)‐double aromatic and π,σ‐mixed aromatic boron compounds with two electrons delocalized over three centers

Hofmann, Matthias; Berndt, A.

doi:10.1002/hc.20225

Cited by 48 publications

(38 citation statements)

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“…These systems parallel the mixed aromatic/antiaromatic systems recently reported by Hofmann and Berndt (Figure 12). [27] Boron and borocarbon clusters: The previously described NICS analyses also establishes double aromaticity in the two boron and eight borocarbon rings studied here (see Figure 13 and Table 1). C 4 B 4 illustrates a 6+6 doubly aromatic borocarbon system (Figure 14).…”

mentioning

confidence: 87%

“…Likewise, the NICS(0) iso value (À35.6) of the 14-membered doubly aromatic polyallene ring (D 7h -C 14 ) is much larger than that of both the D 2h (À13.4) and the D 14h C 14 H 14 (À15.8) forms of the singly (p) aromatic [14]annulene, evidently due to the contribution of the radial in-plane aromatic system of D 7h -C 14 . Hofmann and Berndt [27] examined the double aromaticity of small boron-containing systems, by using enhanced isotropic NICS values as a criterion, and concluded that twoelectron in-plane delocalization was a key feature in their unusual structures. They designed double aromatic molecules containing anionic B 3 , neutral B 3 , and CB 2 frameworks with two in-plane delocalized electrons ( Figure 3).…”

Section: Introductionmentioning

confidence: 99%

“…[26] However, this does not change the basic double aromatic character of the bonding. In another approach, Hofmann and Berndt [27] used the B 3 framework in B 3 H 3 2À and its isoelectronic analogue as a scaffold on which to build other doubly aromatic compounds. Moreover, double aromaticity need not be confined to small systems or simple rings; several double-aromatic structures, including boron wheels [28,29] and trannulene-type double boron rings, [30] have also been investigated.…”

Section: Introductionmentioning

confidence: 99%

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Double Aromaticity in Monocyclic Carbon, Boron, and Borocarbon Rings Based on Magnetic Criteria

Wodrich

Corminbœuf

Schleyer

2007

Chemistry A European J

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The double-aromatic character of selected monocyclic carbon, boron, and borocarbon rings is demonstrated by refined nucleus-independent chemical shift (NICS) analyses involving the contributions of individual canonical MOs and their out-of-plane NICS tensor component (CMO-NICS(zz)). The double aromaticity considered results from two mutually orthogonal Hückel p AO frameworks in a single molecule. The familiar pi orbitals are augmented by the in-plane delocalization of electrons occupying sets of radial (rad) p orbitals. Such double aromaticity is present in B(3) (-), C(6)H(3) (+), C(6) (4+), C(4)B(4) (4+), C(6), C(5)B(2), C(4)B(4), C(2)B(8), B(10) (2-), B(12), C(10), C(9)B(2), C(8)B(4), C(7)B(6), C(6)B(8), and C(14). Monocyclic C(8) and C(12) are doubly antiaromatic, as both the orthogonal pi and radial Hückel sets are paratropic. Planar C(7) and C(9) monocycles have mixed aromatic (pi) and antiaromatic (radial) systems.

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mentioning

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Double Aromaticity in Monocyclic Carbon, Boron, and Borocarbon Rings Based on Magnetic Criteria

Wodrich

Corminbœuf

Schleyer

2007

Chemistry A European J

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“…For the c-C 5 BH 3 molecule the contribution to the diatropic ring current from π-delocalized electrons is further decreased from the induced paratropic ring current due to the π-R z transition. Hofmann and Berndt [90] showed that the the NICS(1) values of the double aromatic isoelectronic [c-C 6 H 3 ] + and c-C 5 BH 3 molecules are significantly larger than that of the benzene molecule due to the contribution of an additional aromatic system, namely the σ-aromatic component. Akin to c-C 6 (D 3h ) the c-C 10 (D 5h ) cluster was also proved to be a double (σ + π)-aromatic molecule with enhanced aromaticity due to an additional diatropic subsystem (the diatropic in-plane radial system) [16].…”

Section: The Nics Zz -Scan Curves Versus the Orbital-type Of Aromaticmentioning

confidence: 99%

Diagnosis of the σ-, π- and (σ+π)-Aromaticity by the Shape of the NICSzz-Scan Curves and Symmetry-Based Selection Rules

2010

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Abstract. The NICS zz -scan curves of aromatic organic, inorganic and "all-metal" molecules in conjunction with symmetry-based selection rules provide efficient diagnostic tools of the σ-, π-and/or double (σ + π)-aromaticity. The NICS zz -scan curves of σ-aromatic molecules are symmetric around the z-axis, having half-band widths approximately less than 3 Å with the induced diatropic ring current arising from T x,y -allowed transitions involving exclusively σ-type molecular orbitals. Broad NICS zz -scan curves (half-band width approximately higher than 3 Å) characterize double (σ + π)-aromaticity, the chief contribution to the induced diatropic ring current arising from T x,y -allowed transitions involving both σ-and π-type molecular orbitals. NICS zz -scan curves exhibiting two maxima at a certain distance above and below the molecular plane are typical for (σ + π)-aromatics where the π-diatropic ring current overwhelms the σ-type one. In the absence of any contribution from the σ-diatropic ring current, the NICS zz (0) value is close to zero and the molecule exhibits pure π-aromaticity.

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“…[3] It has been shown that main-group clusters may exhibit multiple aromaticity (s and p), multiple antiaromaticity (s and p), and conflicting aromaticity (s aromaticity and p antiaromaticity or s antiaromaticity and p aromaticity). [4][5][6] Here, we report experimental and theoretical evidence of d aromaticity, which is only possible in transition-metal systems. It is discovered in the [Ta 3 O 3 ]…”

mentioning

confidence: 96%

δ Aromaticity in [Ta₃O₃]⁻

Zhai

Аверкиев²,

Zubarev³

et al. 2007

Angew Chem Int Ed

136

119

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The concept of aromaticity was introduced into organic chemistry to describe delocalized p bonding in planar, cyclic, and conjugate molecules possessing (4n+2) p electrons.[1] In recent years, this concept has been advanced into main-group molecules including organometallic compounds with cyclic cores of metal atoms [2] and, in particular, all-metal clusters.[3]It has been shown that main-group clusters may exhibit multiple aromaticity (s and p), multiple antiaromaticity (s and p), and conflicting aromaticity (s aromaticity and p antiaromaticity or s antiaromaticity and p aromaticity). [4][5][6] Here, we report experimental and theoretical evidence of d aromaticity, which is only possible in transition-metal systems. [7] in which they showed the presence of a new type of chemical bond-a d bond between the two Re atoms. Since then, a branch of inorganic chemistry has been developed that involves multiple metal-metal bonding [8] with bond orders higher than three, the maximum allowed for main-group systems. Power and co-workers recently reported the synthesis of a Cr 2 compound with a quintuple bond (s 2 p 4 d 4 ) between the two Cr atoms. [9] This work, along with recent quantum chemical studies of multiple bonds in U 2 and [Re 2 Cl 8 ] 2À , [10] has generated renewed interest in multiple metal-metal bonding. [11][12][13] The presence of d bonds between two transition-metal atoms suggests that multicenter transition-metal species with a completely delocalized cyclic d bond may exist, thus raising the possibility of d aromaticity analogous to p or s aromaticity in main-group systems. We have been interested in understanding the electronic structure and chemical bonding of early transition-metal oxide clusters as a function of size and composition, and in using them as potential molecular models for oxide catalysts. [14][15][16] During our investigation of tantalum oxide clusters, we found the presence of d aromaticity in the [ Ta 3 O 3 ] À cluster, in which each Ta atom is in a low oxidation state of Ta II and still possesses three electrons for Ta-Ta bonding.The experiment was conducted by using a magneticbottle-type photoelectron spectroscopy apparatus equipped with a laser vaporization cluster source.[17] [Ta m O n ] À clusters with various compositions were produced by laser vaporization of a pure tantalum disk target in the presence of a helium carrier gas seeded with O 2 , and were size-separated by time-of-flight mass spectrometry. The [Ta 3 O 3 ] À species was mass-selected and decelerated before photodetachment by a pulsed laser beam. Photoelectron spectra were obtained at two relatively high photon energies, 193 nm (6.424 eV) and 157 nm (7.866 eV), to guarantee access to all valence electronic transitions (Figure 1). Three well-resolved bands (X, A, and B) were observed at the lower-binding-energy side. The X band is much more intense and shows a discernible splitting at 193 nm (Figure 1 a). Surprisingly, no well-defined electronic transitions were observed beyond 3.7 eV, where continuous signals were...

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(π+σ)‐double aromatic and π,σ‐mixed aromatic boron compounds with two electrons delocalized over three centers

Abstract: Using Schleyer's measure for aromaticity, computed nuclear independent chemical shifts (NICS), we review molecules with two electrons de SCOPE AND LIMITATIONSThe following reviews experimental and computed results on ( + )-double aromatic and ,-mixed

Cited by 48 publications

References 96 publications

Double Aromaticity in Monocyclic Carbon, Boron, and Borocarbon Rings Based on Magnetic Criteria

Double Aromaticity in Monocyclic Carbon, Boron, and Borocarbon Rings Based on Magnetic Criteria

Diagnosis of the σ-, π- and (σ+π)-Aromaticity by the Shape of the NICSzz-Scan Curves and Symmetry-Based Selection Rules

δ Aromaticity in [Ta₃O₃]⁻

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(π+σ)‐double aromatic and π,σ‐mixed aromatic boron compounds with two electrons delocalized over three centers

Abstract: Using Schleyer's measure for aromaticity, computed nuclear independent chemical shifts (NICS), we review molecules with two electrons de SCOPE AND LIMITATIONSThe following reviews experimental and computed results on ( + )-double aromatic and ,-mixed

Cited by 48 publications

References 96 publications

Double Aromaticity in Monocyclic Carbon, Boron, and Borocarbon Rings Based on Magnetic Criteria

Double Aromaticity in Monocyclic Carbon, Boron, and Borocarbon Rings Based on Magnetic Criteria

Diagnosis of the σ-, π- and (σ+π)-Aromaticity by the Shape of the NICSzz-Scan Curves and Symmetry-Based Selection Rules

δ Aromaticity in [Ta3O3]−

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δ Aromaticity in [Ta₃O₃]⁻