Isolation of Free Phenylide-like Carbanions with N-Heterocyclic Carbene Frameworks

Abstract

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 analogs 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 sp 2 -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 2 a charge distribution analysis, and the relationship between phenylide-type carbanions and Nheterocyclic carbenes is discussed through the prism of the results reported herein.

Ambiphilic boron in 1,4,2,5-diazadiborinine

“…Experimental and computational studies on the reactivity demonstrate a manifesting dual character of the boron atoms in 2 , which is capable of activating a series of small molecules under mild reaction conditions. Such chemical behaviour has never been observed for the previously reported B 2 C 2 N 2 heterocycles 57 58 59 . As the substituents on the boron and nitrogen atoms in 1,4,2,5-diazadiborinine can be readily modified, the steric and electronic properties as well as the reactivity could be finely tunable.…”

Anionic N-heterocyclic carbenes derived from sydnone imines such as molsidomine. Trapping reactions with selenium, palladium, and gold

“…63 All final structures were proven to be true minima by the absence of imaginary frequencies or transition states by the occurrence of a negative frequency. (10). Into a 250 mL flask N-(o-methoxyphenyl)-aminoacetonitrile (10.60 g, 65.4 mmol) and 50 mL of hydrochloric acid (12.5 %) were given and cooled to 0 °C.…”

“…Currently, the design and the syntheses of anionic Nheterocyclic carbenes 1 including ditopic carbanionic Nheterocyclic carbenes 2 and anionic dicarbenes [3][4][5] constitute an important topic in structural, complex, synthetic and catalytic chemistry. To date, anionic NHCs have been generated by deprotonation of neutral N-heterocycles, [6][7][8][9][10] by incorporation of anionic groups into the NHC backbone, [11][12][13][14][15] or by reduction of an NHC in the presence of a metal. [16][17][18] Consequently, several types of anionic N-heterocyclic carbenes have been prepared which can be differentiated i.a.…”

Unexpected Formation and Crystal Structure of the Highly Symmetric Carbanion [C(SiCl3)3]–

“…Harder has hinted recently to that fact and proved these early results by the X‐ray structure analysis of [Me 4 N][Ph 3 C] . Looking at the body of literature, one can state that free carbanions are stabilized by employing resonance to decrease the charge density on the carbon center and hence reduce its basicity . Suitable substituents that have been applied so far are electron‐withdrawing groups like CN or NO 2 , alkyl‐ and arylsilyl substituents, and aromatic groups.…”