Triboracyclopropanates: Two-Electron Double Aromatic Compounds with Very Short BB Distances

Präsang, Carsten; Młodzianowska, Anna; Şahin, Yüksel; Hofmann, Matthias; Geiseler, Gertraud; Massa, Werner; Berndt, A.

doi:10.1002/1521-3773(20020916)41:18<3380::aid-anie3380>3.0.co;2-8

Cited by 55 publications

(32 citation statements)

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“…On the other hand, for the latertransition-metal centers, and in particular for Fe and Co, the remarkable enhancement of both the s and the p aromaticity renders the N 4 ring doubly aromatic, a concept first introduced by Schleyer and co-workers [13] and then experimentally confirmed by Berndt and co-workers. [14,15] Nickel does not alter the s antiaromatic and p aromatic character of the N 4 2À ring upon complexation.…”

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confidence: 99%

Mono‐ and Multidecker Sandwich‐Like Complexes of the Tetraazacyclobutadiene Aromatic Ring

2004

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Dedicated to Professor Cecilia SarasolaSince the fortuitous discovery [1] of ferrocene, [(C 5 H 5 ) 2 Fe], the cyclopentadienyl anion has emerged as the most versatile aromatic ring for the synthesis of sandwich-like complexes. Indeed, it has been estimated that more than 80 % of all known organometallic complexes of transition metals contain a substituted or unsubstituted cyclopentadienyl ligand. [2] Nevertheless, new aromatic compounds have recently been identified whose incorporation into sandwich complexes opens new routes for chemical creativity. In particular, we have predicted [3] that the all-metal [Al 4 ] 2À aromatic ring [4] can complex Ti to form [Al 4 TiAl 4 ]2À . The tetraazacyclobutadiene dianion, N 4 2À , also fulfills the aromaticity requirements.[5] It has a square-planar structure with six delocalized p electrons, four of which occupy the nonbonding p highest occupied molecular orbitals (HOMOs); the other two p electrons participate effectively in the aromatic stabilization, in agreement with the (4 n+2) rule. The nucleus-independent chemical shift (NICS) [6] at 1.0 above the molecular plane is À4.09 ppm, [7] confirming further the p-aromatic character of the ring. Consequently, N 4 2À can, in principle, be incorporated into sandwich-like complexes although, as far as we know, no such structures have been reported to date.We have therefore theoretically characterized stable sandwich-type complexes of the N 4 2À aromatic ring with early (Ti, V, and Cr) and late (Fe, Co, and Ni) transition-metal centers, with charges 2À (Ti, Fe), 1À(V, Co), and 0 (Cr, Ni). The optimized structure of the Ti sandwich-like complex has D 4h symmetry; the V and Cr analogues have C 2v symmetry, although they can also be viewed as bent D 4h structures (Figure 1). The optimum geometries of the late-transitionmetal complexes have D 4d symmetry. Consequently, for the complexes of the early-transition metals the nitrogen atoms are eclipsed whereas they are staggered for those of the late transition metals.The calculations were carried out with the B3LYP functional, as implemented in Gaussian 98, [8] with the standard 6-311G basis set.

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confidence: 99%

Mono‐ and Multidecker Sandwich‐Like Complexes of the Tetraazacyclobutadiene Aromatic Ring

2004

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“…Consequently,t hese compounds are both sand p-homoaromatic compounds [(p + s)-double aromatic]. [5,28] These compounds are related to an isomer (also C 2v -symmetric) of (B 3 H 4 ) À that is slightly higher in energy than the global energy minimum structure.T hey exhibit both s-a nd p-delocalized electron systems,and can thus be classified as (p + s)-double aromatic compounds. [26] Formal monoprotonation of (B 3 H 3 ) 2À leads to (B 3 H 4 ) À (Scheme 4).…”

Section: Synthesis Structure and Electron-deficient Bonding Of B 3 mentioning

confidence: 99%

Electron‐Deficient Triborane and Tetraborane Ring Compounds: Synthesis, Structure, and Bonding

Himmel

2019

Angew Chem Int Ed

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Electron‐deficient small boron rings are unique in their formation of σ‐ and π‐delocalized electron systems as well as the avoidance of “classical” structures with two‐center‐two‐electron (2c,2e) bonds. These rings are tolerant of several skeletal electron numbers, which makes their redox chemistry highly interesting. In the past few decades, a range of stable compounds have been synthesized with various electron numbers in their B3 and B4 cores. The electronic structures were evaluated by quantum‐chemical calculations. On the other hand, the chemistry of these rings is still very much underdeveloped, being generally limited to the protonation and redox reactions of individual systems. The linkage of several B3 and/or B4 ring systems should give compounds with attractive electronic properties, thus leading the way to novel boron‐based materials. By summarizing important experimental and theoretical results, this Review intends to provide the basis for the exploration of the chemistry of these rings and, in particular, their integration into larger molecular architectures.

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“…[46][47][48] Multiple fold aromaticity generally are applicable to molecules that possess more than one independent delocalized bonding systems, either -type or -type, each of them satisfying Huckel's (4n + 2) electron counting rule of aromaticity. 49 The doubly-aromatic molecules are found to be significantly more stable with higher resonance energies, shortened bond lengths, enhanced ring currents, more negative nucleus-independent chemical shift (NICS) values than conventional singly-aromatic molecules like benzene or anthracene.…”

Section: The Electronic Structure Of Isolatedmentioning

confidence: 99%

‘All-Metal’ Aromatic Sandwich Molecules: An Electronic Structure and Transport Study

Das¹

2015

j nanosci nanotechnol

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Electronic structure and transport is theoretically studied for neutral, all-metal aromatic sandwich molecules, Al4MAl4 (M = Cr, Mo) along with Al4 and Al4M (M = Cr, Mo) clusters in two-probe setups with silver and gold electrodes. Detailed electronic structure and transport studies of metallaromatic Al4MAl4 molecules show high electronic conductance [2.5*10(-4) S for Al4CrAl4 and 2.9*10(-4) S for Al4MoAl4] and three conduction channels simultaneously contribute to the total transmission probability. The study of transport properties of the bare Al4 cluster and Al4M cluster also show very high electronic conductance. The neutral Al4 cluster, when connected parallel to the electrodes, four Al atoms couple to the electrode atoms and at least eight electron conduction pathways contribute simultaneously to the conductance whereas for perpendicular connectivity only three conduction channels operate. All the molecules couple strongly to the electrodes by well-defined metal-metal bonds owing to their metallic nature indicating an easier electrode integration process, and the calculated current voltage curves are almost linear till applied voltages of 1 V for Al4MAl4 (M = Cr, Mo). The electronic transport of the clusters studied here resembles the values found for metal atomic chains in break junction studies.

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Triboracyclopropanates: Two-Electron Double Aromatic Compounds with Very Short BB Distances

Abstract: One extremely short and two relatively long BB bonds are found for the B3 ring of compounds 1 and 2. This characteristic of three‐membered, two‐electron double aromatic compounds was predicted as early as 1994 and has now been experimentally realized for the first time. A=SiMe3.

Cited by 55 publications

References 5 publications

Mono‐ and Multidecker Sandwich‐Like Complexes of the Tetraazacyclobutadiene Aromatic Ring

Mono‐ and Multidecker Sandwich‐Like Complexes of the Tetraazacyclobutadiene Aromatic Ring

Electron‐Deficient Triborane and Tetraborane Ring Compounds: Synthesis, Structure, and Bonding

‘All-Metal’ Aromatic Sandwich Molecules: An Electronic Structure and Transport Study

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