Electronic nature of the aromatic adamantanediyl ions and its analogues

Abstract

A estabilidade relativa do dicátion 1,3-desidro-5,7-adamantanediila é atribuída a sua aromaticidade tridimensional. Contudo, sua natureza eletrônica não é bem conhecida. A fim de entendê-la melhor, os di-e monocátions do adamantanodiil e alguns de seus análogos foram estudados utilizando a teoria de átomos e moléculas (AIM). Eles foram comparados com análogos de adamantano não-aromáticos. Os resultados de AIM indicam que a densidade eletrônica no centro da estrutura em gaiola e a média de todos os índices de deslocalização, envolvendo seus átomos cabeças-de-ponte são maiores em compostos aromáticos do que em não-aromáticos. A degenerescência energética dos átomos cabeça-de-ponte, a uniformidade e magnitude da carga compartilhada entre estes, distingue os dicátions 1,3-adamantila e 1,3-desidro-5,7-adamantanediila. Contudo, ambos são aromáticos, assim como o 1,3-desidro-5,7-diboroadamantano. O cátion 1,3-desidro-7-adamantila tem uma homoaromaticidade planar característica.The relative stability of the 1,3-dehydro-5,7-adamantanediyl dication is ascribed to its tridimensional aromaticity. However, its electronic nature is not well known. In order to improve its understanding, dicationic and monocationic adamantanedyil species and some key analogues were studied by atoms in molecules (AIM) theory. They were compared to non-aromatic adamantane analogues. AIM results indicate that the density in center of the cage structure and the average of all delocalization indexes involving its bridged atoms are higher in aromatic than in non-aromatic compounds. Degeneracy in energy of the bridged atoms, uniformity and magnitude of their shared charge distinguish the dications 1,3-adamantyl and the 1,3-dehydro-5,7-adamantanediyl. However, both are aromatic as well as the 1,3-dehydro-5,7-diboroadamantane. The 1,3-dehydro-7-adamantyl cation has a characteristic planar homoaromaticity.Keywords: adamantyl dication, adamantyl cation, degeneracy, delocalization index, ring density, aromaticity, tridimensional aromaticity, 1,3-dehydro-5,7-adamantanediyl dication IntroductionSome cationic adamantanediyl species are relatively stable intermediates, e.g., Schleyer's 1,3-dehydro-5,7-adamantanediyl dication (Scheme 1). The adamantanediyl monocation is a stable species and can be synthesized from the 1-adamantanol and fluorosulfonic acid-antimony pentafluoride.1 The adamantanediyl dication has not been observed as persistent long-lived species so far.2 Ionization of 1,3-difluoroadamantane in superacids afforded only the monocation complex 3 C 10 H 14 F-SbF 5 (Scheme 1). Attempts of obtaining other adamantane-1,3-diyl dications were not successful. 4 However, the 1,3-dehydro-5,7-adamantanediyl dication (or 1,3,5,7-bisdehydroadamantane dication) is a stable species.5 It exhibits shielded bridgehead carbons at 6.6 ppm with methylene carbon resonances appearing at 35.6 ppm which is characteristic of hypercoordinate carbocations. 5 Despite that 1,3,5,7-tetrasilaadamantane (Scheme 1) is easily obtained 6 from the 1,3,5-hexamethyl-1,3,5-trisilacycl...

Double hydrogen bond interaction in 7-azaindole complexes with protic solvents

“…The vibrational frequencies for all optimized structures were detected as real. The previous investigations on DHBs have been demonstrated that the Becke-Lee-Yang-Parr density functional theory is able to successfully predict the geometry, electronic and energetic properties of 7AI complexes in the ground electronic state [10, 27,28]. Basis set superposition error (BSSE) correction has been applied to energy calculations based on the Boys and Bernardi counterpoise method [29].…”

Stability and electronic structures of substituted tetrahedranes, silicon and germanium parents – a DFT, ADMP, QTAIM and GVB study

“…The GVB singly occupied orbitals were calculated from VB/6-31G level theory and they were generated by means of Molekel visualization program. We will use the same D3BIA formula for homoaromatic species 41 where the electron density is associated with the charge density of the ring critical point (for 3c-2e bonding systems, for example) or of the cage critical point (for the tridimensional 4c-2e bonding system). 35,38 Nucleus Independent Chemical Shift (NICS) 39 and Density, Degeneracy, Delocalization-Based Index Aromaticity (D3BIA) 40 were applied to determine the aromaticity in tetrahedrane and its derivatives.…”

Electronic structures of bisnoradamantenyl and bisnoradamantanyl dications and related species

“…It is important to emphasize that the delocalization index of a very weak C-C interaction is on the order of 10 −2 to 10 −3 . Moderately strong C-C interactions have DI values on the order of 10 −1 [38][39][40].…”

“…Moreover, we also noticed the influence of the uniformity of the delocalization index over the whole aromatic site on the stability of a chemical species. For example, we observed that the large difference in stability between the (isolated and characterized) 4,9-diamantyl dication and the (yet-to-be-isolated) 1,6-diamantyl dication can be attributed to the higher uniformity of the delocalization indices among the carbon atoms in the former [39]. We therefore proposed the following formula for the delocalization index uniformity (DIU):…”