Synthesis and Structure of a Hexacoordinate Carbon Compound

Abstract

In an exploration of six coordination and hypervalence in carbon compounds, steric constraints have been employed to bring four ether O atoms in close proximity to an allenic carbon atom. The dimethylated dication 2 is confirmed to have hexacoordinate carbon by experimental charge density analysis and DFT calculations and is arguably hypervalent.

Crystal Structure Determination of the Pentagonal‐Pyramidal Hexamethylbenzene Dication C6(CH3)62+

“…Theu pfield-shifted resonance at 21.0 ppm is typical for acarbocation with ahigh coordination number and can be assigned to the top of the pyramid, while the signal at À4.5 ppm belongs to the attached methyl group. Thev ery unusual (in ad ication) slightly negative chemical shift of the apical methyl group in the 13 CNMR prompted us to apply Schleyersn ucleus-independent chemical shift (NICS) criterion [27] to investigate the magnetic shielding in C 6 (CH 3 ) 6 2+ .T he values of NICS(0.5) À40.553 and NICS(1) À41.004 inside the pyramidal cone are larger than NICS-(À0.5) À13.878 and NICS(À1) À9.262, but they all indicate the presence of induced diatropic ring currents,w hich is typical for athree-dimensional aromatic system. In summary,t he non-classical C 6 (CH 3 ) 6 2+ dication was prepared as the SbF 6 À salt through the dissolution of hexamethyl Dewar benzene epoxide in magic acid.…”

“…TheC À Odistances are in the range of 2.43(1)-2.45(1) and 2.641(5)-2.750(5) ,r espectively, [12,13] thus indicating only weak interactions.Instark contrast, hypercoordinated carbon with much shorter bonds can be found in carboranes. Nevertheless,t hese common structural motives of boron chemistry are only subtly changed by replacing boron with an isolobal carbon fragment.…”

“…[11] Taking ac ompletely different approach, Akiba and co-workers prepared formally hypercoordinated organic species through special ligand design, where an electrophilic carbon atom is intramolecularly coordinated by two/four neighboring methoxy groups. TheC À Odistances are in the range of 2.43(1)-2.45(1) and 2.641(5)-2.750(5) ,r espectively, [12,13] thus indicating only weak interactions.Instark contrast, hypercoordinated carbon with much shorter bonds can be found in carboranes. Nevertheless,t hese common structural motives of boron chemistry are only subtly changed by replacing boron with an isolobal carbon fragment.…”

“…Nevertheless,t he formation of pentagonal-pyramidal C 6 (CH 3 ) 6 2+ can be additionally explained by the reaction mechanism (see Figure S9). C 6 (CH 3 ) 6 2+ gives two signals in the 1 HNMR at À60 8 8C, one at 2.51 ppm corresponds to the five basal methyl groups, while the peak at 1.85 ppm corresponds to the apical methyl group.T he 13 Cs pectrum exhibits four signals.Asinglet at 8.5 ppm can be observed for the basal methyl groups,w hile the singlet of the carbon atoms of the five-membered ring appears at 125.3 ppm. Theu pfield-shifted resonance at 21.0 ppm is typical for acarbocation with ahigh coordination number and can be assigned to the top of the pyramid, while the signal at À4.5 ppm belongs to the attached methyl group.…”

Wann bilden wechselwirkende Atome eine chemische Bindung? Spektroskopische und theoretische Analyse an Dideuterophenanthren

“…B. Lit. [7]). Der strittigste Aspekt dieser Interpretation ist das Konzept der H-H-Bindung, das von Matta et al eingeführt wurde.…”