Isolation of Free Phenylide-like Carbanions with N-Heterocyclic Carbene Frameworks
Krahulic, K., Tuononen, H., Parvez, M., & Roesler, R. (2009). Isolation of Free Phenylide-like Carbanions with N-Heterocyclic Carbene Frameworks. Journal of the American Chemical Society, 131(16), 5858-5865. https://doi.org/10.1021/ja9001234
Published inJournal of the American Chemical Society
© 2009 American Chemical Society. This is a final draft version of an article whose final and definitive form has been published by ACS. Published in this repository with the kind permission of the publisher.
A series of 1,3-bis(2,6-diisopropylphenyl)-5-methyl-1,3-diaza-4,6-diborabenzenes with methyl, phenyl, and dimethylamino substituents on the ring boron atoms were prepared using the cyclocondensation reaction between N,N′-bis(2,6-diisopropylphenyl)trimethylsilylformamidine and the appropriately substituted 1,1-bis(organochloroboryl)ethane, followed by deprotonation of the cationic ring intermediate. The planar, heterocyclic benzene analogues could be further deprotonated at the other ring carbon using an additional equivalent of potassium hexamethyldisilazide to yield organometallic derivatives akin to the potassium phenylide. The potassium cations could be efficiently sequestered in both solution and solid state using 18-crown-6, and the crystallographic analysis of the reaction products revealed the absence of carbanion−cation contacts in the solid state. The transformation of a planar, tricoordinate sp2 carbon to a tricoordinate, contact ion-pair carbanion and further to a solvent-separated, free dicoordinate carbanion was investigated using solution NMR and single-crystal X-ray diffraction. The first isolation and characterization of free dicoordinate carbanions in the solid state is supported by a charge distribution analysis, and the relationship between phenylide-type carbanions and N-heterocyclic carbenes is discussed through the prism of the results reported herein. ...
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