Planar-Tetracoordinate Carbon in a Neutral Saturated Hydrocarbon: Theoretical Design and Characterization

Abstract

Exact planarity at the central carbon atom is achieved, according to molecular orbital calculations, in the strained polycyclic cage hydrocarbon dimethanospiro[2.2]octaplane (see structure). There are no glaringly long C−C bonds, which might have reflected inherent instability in this molecule that is yet to be synthesized.

Ring Currents in a Proposed System Containing Planar Hexacoordinate Carbon, CB62−

“…[1,2] Nevertheless, even this near-universal rule has its exceptions. Predicted planar geometries for carbon in fourfold coordination [3±7] have been verified in a small number of cases, [8±11] and in recent theoretical explorations of the boundaries of carbon chemistry, [12,13] even more exotic planar hexacoordinate carbon atoms have been proposed for species such as CB 6 2À . One motivation given by Exner and Schleyer for considering such high coordination numbers was the potential for discovery of new aromatic systems.…”

“…[12] One popular probe of aromaticity on the magnetic criterion is the NICS (nucleus-independent chemical shift) [14] computed at or above ring centres and compared with a benzene standard. Such comparisons are less clearcut for systems with a central atom, but the computed shifts at 1.0 and 1.5 ä above the ring centre (d À 22.8/ À 9.7) have been taken to suggest aromaticity [12] for CB 6 2À . Herein we take up this theme and explore the consequences of the unusual hexacoordinate bonding environment directly for the main diagnostic of aromaticity: the ring current [14±17] itself.…”

Recent advances in planar tetracoordinate carbon chemistry

“…Alkaplanes are the best examples. 16,[50][51][52][53][54][55] However, so far attempts to synthesize a ptC molecule using the mechanical approach have failed. In 1999, Keese and coworkers noted that ''despite considerable computational efforts no structures with a planar tetracoordinate C(C) 4 substructure have been found.''…”

“…3). 51 Using a similar approach, Wang and Schleyer found a set of boron spiroalkanes with a planar C(C) 4 core through substitution of carbon by boron atoms. 24,57 Both suggestions are based on the mechanical approach.…”

Extending the Chemistry of [5.5.5.5]Fenestranes − Eightfold Peripheral Functionalization of Fenestrindanes

“…This motif is now of interest not only in organic but also in metalorganic [4] and inorganic chemistry, [5] and inspiration from theoretical chemistry may lead to further developments in the organic chemistry of flattened or planar tetracoordinate carbon. [6] However, the synthetic utility of fenestranes as building blocks in organic chemistry has not been exploited to any great extent, [7] and only the facile access to benzoannelated derivatives of [5.5.5.5]-and [5.5.5.6]fenestranes has opened promising routes to extended molecular frameworks bearing the three-dimensional fenestrane core. [2,8Ϫ10] In a similar way to related aromatic hydrocarbons of the centropolyindane family, [10] and in particular the tribenzotriquinacenes, [11,12] the prototype of the benzoannelated fenestranes, fenestrindane 1, [13] offers two different possibilities for the creation of novel molecular architectures: (i) Bridgehead functionalization, e.g.…”