Heterobuckybowls:  A Theoretical Study on the Structure, Bowl-to-Bowl Inversion Barrier, Bond Length Alternation, Structure-Inversion Barrier Relationship, Stability, and Synthetic Feasibility

Abstract

Hybrid density functional theory (DFT) calculations at the B3LYP/cc-pVDZ level have been performed on a series of heterobuckybowls, 3X, C(18)X(3)H(6) (X = O, NH, CH(2), BH, S, PH, PH(3), Si, SiH(2), and AlH). The minimum energy conformations and the transition states for bowl-to-bowl inversion, where the geometry is bowl shaped, are computed and characterized by frequency calculations. The geometries of heterotrindenes, 2X, C(12)X(3)H(6) (X = O, NH, CH(2), BH, S, PH, PH(3), Si, SiH(2), and AlH), were obtained, and the bond length alternation (Delta) in the central benzenoid ring shows remarkable sensitivity as a function of substituent with a wide range of fluctuations (-0.014 to +0.092 A). The Delta computed in 2BH was found to be comparable with the highest bond alternation reported to date in benzenoid frameworks. The inversion dynamics of these heterobowls and their bowl depths were fit to a mixed quartic/quadratic function. The size of the heteroatom seems to exclusively control the bowl depth and rigidity as well as the synthetic feasibility. In contrast, the bond length alternation seems to be controlled by electronic factors and not by the size of the substituted atom either in trindenes or in heterosumanenes. The thermodynamic stability of this class of compounds is very much comparable with trithiasumanene (3S), which has been synthesized recently. The chemical hardness (eta) was measured to assess the stability of the heterosumanenes. The strain energy buildup in a sequential ring closure strategy along two synthetic routes, namely a triphenylene route and a trindene route, were explored, and the trindene route was found to be highly favorable for making such compounds compared to the triphenylene route. However, in both routes the ease of the synthetic feasibility increases as the size of the heteroatom increases.

Enantioselective synthesis of a chiral nitrogen-doped buckybowl

“…Heterobuckybowls doped by larger heteroatoms other than carbon such as S, Si and Sn exhibited less curvature, resulting in shallower bowls or planar structures [16][17][18] . In contrast, azabuckybowls doped by nitrogen atoms, which are smaller than carbon atoms, are predicted by calculations to exhibit more curvature with deeper bowl depth than all-carbon bowls 14 . Synthesis of such a highly strained bowl structure has been a challenging task for a long time 19 .…”

“…Buckybowls have attracted much attention not only as model compounds for fullerenes, but also for their own chemical and physical properties [10][11][12][13] . In contrast to nitrogen-doped fullerenes and CNTs, nitrogen-doped buckybowls, azabuckybowls, still remain unknown except for some theoretical studies 14,15 . Doping of nitrogen to the aromatic skeleton is expected to modulate the curvature, bowl inversion barrier, and physicochemical properties.…”

Chiral Buckybowl Molecules

“…Theoretical studies suggested that doping of nitrogen will lead to deeper and curved bowl depth compared to the all-carbon counterparts [77]. Sakurai and co-workers reported the first chiral nitrogen-doped buckybowl (Scheme 3) [12].…”

Computational studies of π–π interactions in dimers of heterosubstituted sumanenes

“…Several computational studies have been carried out on sumanene and its dimer [13, and references therein] and the monomers of heterosubstituted sumanenes [22][23][24][25][26][27][28]. These studies focused on the monomer geometries, bond alternations, and bowl inversion.…”