The aromaticity of dicupra[10]annulenes

Abstract

An extensive theoretical investigation of the electronic structure of a tested fair model dicupra[10]annulene compound, based on the analysis of atom-pair delocalization indices, Bader's molecular graph, the inspection of the canonical molecular orbitals, the z components of their Nuclear Independent Chemical Shifts, NICS(0), and the normalized Giambiagi multicenter delocalization indices, concludes that the perimeter aromaticity of the dicupra[10]annulene ring is consistent with both 10 and 14 π-electron Hückel aromatic 10-membered rings. In either case, the 10-membered ring encloses two 6 π-electron aromatic inner rings, hinged at the Cu-Cu bond. This work demonstrates that the aromaticity of dicupra[10]annulenes closely resembles that of naphthalene. Hence, they are best regarded as metalla-polyacenes, which could make the building blocks of extended structures such as metalated nanotubes.

Strict Correlation of HOMO Topology and Magnetic Aromaticity Indices in d‐Block Metalloaromatics

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Magnetic aromaticity and antiaromaticityo f closed shell metalloaromaticsw ith 4d transition metals (Nb, Tc ,R h) is strictly correlatedw ith the orbital topology (Mçbiuso rH ückel) of their p-HOMO, investigated computationally with DFT methods. As urprisingly simple rule emerged:t he metallacycle is aromatic (antiaromatic) when the number of p MOs is even and the p-HOMOi so f Mçbius( H ückel) topology-and vice versa when the numbero fp MOs is odd.Recent reports aboutM çbiusa romatic osmapentalenes [1] and Hückel aromatic dicupra[10]annulene tetraanions [2] spikedarenewed interest in understanding the aromaticity of conjugated metallacycles; [3] ap resumably familiar concept, since R. Hoffmann's insightful proposal and the subsequent preparation of the first osma- [4] or iridabenzenes. [5] However,o ne of the most puzzlingf acts about metallabenzenes is that they seem to be limited to late or middle transition metal elements, whereas early transition metals do not seem to form metallabenzenes at all, and coinage metals appear to avoid being involved in neutral( rather than anionic) aromatics.

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Aromaticity of N‐heterocyclic carbene and its analogues: Magnetically induced ring current perspective

“…In order to understand the contribution from different resonance structures as obtained from the NBO results, the CMO‐NICS calculations are performed . For borylene, the contribution to the NICS(0) value from different CMO and NBO are represented in Figures and , and all others are shown in Figures S1‐S22.…”

The aromatic character of [10]annulenes and dicupra[10]annulenes from current density calculations

“…Grande-Aztatzi et al claimed that the annulene structures without substituents exhibit little deviation from the geometry in the substituted molecules. 18 However, this does not hold for A 4 and B 4 . The planar unsubstituted A 4 structure does not represent the experimental B 4 structure very well, since the rings in B 4 are twisted as shown in Figure 14.…”

“…These results suggested that structure A 4 is even more aromatic than naphthalene. 18 Molecular-orbital analysis of the aromatic properties of A 2 and A 4 has recently been reported by An et al 27 They also calculated nucleus independent chemical shifts (NICS(0) zz ) and anisotropy of the induced-current densities (ACID) functions. 17,28 The NICS(0) zz and ACID calculations suggested that A 4 is aromatic and A 2 is antiaromatic.…”

“…The results of the computational studies also suggested that B 4 is aromatic and B 2 is nonaromatic. 12 The dicupra [10]annulene with hydrogen atoms at all carbon atoms and two (A 2 ) or four (A 4 ) lithium ions was recently investigated computationally by Grande-Aztatzi et al 18 They employed the normalised Giambiagi multicentre electron delocalisation index I NG to evaluate the electron density distribution in the molecule, claiming that it is a reliable marker for the aromatic character of the molecules. [19][20][21][22][23][24][25][26] The conclusion based on their calculations was that molecule (A 4 ) and naphthalene have comparable aromatic character.…”