Back to Search Start Over

Stable alkanes containing very long carbon-carbon bonds.

Authors :
Fokin AA
Chernish LV
Gunchenko PA
Tikhonchuk EY
Hausmann H
Serafin M
Dahl JE
Carlson RM
Schreiner PR
Source :
Journal of the American Chemical Society [J Am Chem Soc] 2012 Aug 22; Vol. 134 (33), pp. 13641-50. Date of Electronic Publication: 2012 Aug 08.
Publication Year :
2012

Abstract

The metal-induced coupling of tertiary diamondoid bromides gave highly sterically congested hydrocarbon (hetero)dimers with exceptionally long central C-C bonds of up to 1.71 Å in 2-(1-diamantyl)[121]tetramantane. Yet, these dimers are thermally very stable even at temperatures above 200 °C, which is not in line with common C-C bond length versus bond strengths correlations. We suggest that the extraordinary stabilization arises from numerous intramolecular van der Waals attractions between the neighboring H-terminated diamond-like surfaces. The C-C bond rotational dynamics of 1-(1-adamantyl)diamantane, 1-(1-diamantyl)diamantane, 2-(1-adamantyl)triamantane, 2-(1-diamantyl)triamantane, and 2-(1-diamantyl)[121]tetramantane were studied through variable-temperature (1)H- and (13)C NMR spectroscopies. The shapes of the inward (endo) CH surfaces determine the dynamic behavior, changing the central C-C bond rotation barriers from 7 to 33 kcal mol(-1). We probe the ability of popular density functional theory (DFT) approaches (including BLYP, B3LYP, B98, B3LYP-Dn, B97D, B3PW91, BHandHLYP, B3P86, PBE1PBE, wB97XD, and M06-2X) with 6-31G(d,p) and cc-pVDZ basis sets to describe such an unusual bonding situation. Only functionals accounting for dispersion are able to reproduce the experimental geometries, while most DFT functionals are able to reproduce the experimental rotational barriers due to error cancellations. Computations on larger diamondoids reveal that the interplay between the shapes and the sizes of the CH surfaces may even allow the preparation of open-shell alkyl radical dimers (and possibly polymers) that are strongly held together exclusively by dispersion forces.

Details

Language :
English
ISSN :
1520-5126
Volume :
134
Issue :
33
Database :
MEDLINE
Journal :
Journal of the American Chemical Society
Publication Type :
Academic Journal
Accession number :
22835264
Full Text :
https://doi.org/10.1021/ja302258q