“Carbon Dichloride”: Dihalocarbenes Sixty Years After Hine

Abstract

We describe new syntheses of dichlorodiazirine, difluorodiazirine, and chlorofluorodiazirine. From these precursors, laser flash photolysis enables the generation of CCl(2), CF(2), and CClF. We describe the formation and chemistry of bromodichloromethide carbanion from CCl(2), the ambiplilicity of CCl(2), the complexation of CCl(2) by aromatic ethers, and the kinetics and activation parameters attending the additions of CCl(2), CF(2), and CClF to several alkenes.

Unusual solvation through both p-orbital lobes of a carbene carbon

“…2, [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] Especially, relevant has been the UV-vis/IR-LFP detection of solvent-carbene metastable complexes, previous to the system evolution to typical carbene stable products such as ylides and cyclopropanes, depending of the case. [21][22][23][24][25][26][27][28] This occurs in solvents having nonbonding electrons such as ethers, haloalkanes, and halobenzenes, and solvents having π electrons such as benzene and other unsaturated species. [21][22][23][24][25][26][27][28] Those solvents generate specific solvation by electron density donation to the empty p carbene carbon orbital, temporarily stabilizing the system.…”

“…[21][22][23][24][25][26][27][28] This occurs in solvents having nonbonding electrons such as ethers, haloalkanes, and halobenzenes, and solvents having π electrons such as benzene and other unsaturated species. [21][22][23][24][25][26][27][28] Those solvents generate specific solvation by electron density donation to the empty p carbene carbon orbital, temporarily stabilizing the system. 11,12,[21][22][23] This complexation retards reactions such as additions to olefins to form cyclopropanes, 22,23 or the formation of ylides, by factors of up to 2 orders of magnitude in their rate constants, with respect to the case of absence of stabilizing solvents.…”

“…[21][22][23][24][25][26][27][28] Those solvents generate specific solvation by electron density donation to the empty p carbene carbon orbital, temporarily stabilizing the system. 11,12,[21][22][23] This complexation retards reactions such as additions to olefins to form cyclopropanes, 22,23 or the formation of ylides, by factors of up to 2 orders of magnitude in their rate constants, with respect to the case of absence of stabilizing solvents. 24 Parallel to the experimental findings, there have been theoretical efforts for describing this specific carbene solvation.…”

“…24 Parallel to the experimental findings, there have been theoretical efforts for describing this specific carbene solvation. 12,[21][22][23][24][25][26][27][28] In some of these studies, it has been proposed 1:1 complexes, with respect to the carbene:solvent molecular relationship. Candidate carbene-solvent structures are subjected to geometrical optimizations via traditional methods, usually within the framework of the density functional theory (DFT).…”

“…Candidate carbene-solvent structures are subjected to geometrical optimizations via traditional methods, usually within the framework of the density functional theory (DFT). By means of this procedure, Moss et al 12,[21][22][23][25][26][27] have postulated two classes of complexes: one of "π" type, where the carbene carbon interacts directly with the π system of the solvent aromatic ring. The other is the so-called "ylide complex," wherein a lone pair of a solvent molecule interacts with the carbene carbon.…”