Solvent-Equilibrated Ion Pairs from Carbene Fragmentation Reactions

Abstract

[R(+) OC Cl(-)] ion pairs were generated in methanol/dichloroethane solutions, with R(+) as the 1-bicyclo[2.2.2]octyl, 1-adamantyl, or 3-homoadamantyl cation. Ion pairs were produced either by the direct fragmentation of alkoxychlorocarbenes (ROCCl), with R = 1-bicyclo[2.2.2]octyl, 1-adamantyl, or 3-homoadamantyl, or by the ring expansion-fragmentation of R'CH(2)OCCl, with R' = 1-norbornyl, 3-noradamantyl, or 1-adamantyl. Correlations of the [ROMe]/[RCl] product ratios as a function of the mole fraction of MeOH in dichloroethane showed that the homoadamantyl chloride ion pairs, produced by either the direct or ring expansion-fragmentations, were identical, solvent- and anion-equilibrated, and precursor independent. Laser flash photolysis experiments gave 20-30 ps as the time required for solvent equilibration and precursor independence. Methanol/chloride selectivities of the (less-stable) 1-adamantyl chloride and 1-bicyclo[2.2.2]octyl chloride ion pairs were not independent of their ROCCl or R'CH(2)OCCl precursors. Computational studies provided transition states for the fragmentations and for the structures of the ion pairs.

Adventures in Reactive Intermediate Chemistry: A Perspective and Retrospective

“…Consider Scheme 3, in which the homoadamantyl chloride ion pair 38 is generated either directly by fragmentation of homoadamantyloxychlorocarbene 39 or by fragmentation−ring expansion of adamantylmethoxychlorocarbene 40. 96 In DCE/methanol solvent, the products are the homoadamantyl chloride 41 and the corresponding methyl ether 42. The dependence of the 42/41 product ratio on the concentration of MeOH in the DCE solvent is identical from either carbene 39 or 40, suggesting that ion pair 38 has become solvent equilibrated regardless of its source.…”

“…The dependence of the 42/41 product ratio on the concentration of MeOH in the DCE solvent is identical from either carbene 39 or 40, suggesting that ion pair 38 has become solvent equilibrated regardless of its source. 96 An estimate of the lifetime of the solvent-equilibrated ion pair can be made from LFP time-resolved cation trapping experiments using trimethoxybenzene as the cation trap. 90 We…”

Computational methods for contemporary carbene chemistry

“…Halo‐ and dihalocarbenes are furthermore essential to mechanistic studies in physical organic chemistry and continue to provide insight into the elemental reactivity patterns of carbenes in general. The most extensive studies about various kinds of chlorocarbenes were conducted by Moss et al,93 in the course of which fragmentation patterns and solvation behavior could comprehensively be investigated both experimentally and computationally. Moss et al93 discussed the solvo‐lysis of several alkoxychlorocarbenes, such as 1‐bicyclo[2.2.2]octyloxychlorocarbene, 1‐adamantyl‐oxychlorocarbene ( 9 ), 3‐homoadamantyloxychloro‐carbene, 1‐norbornyloxychlorocarbene, 1‐norborn‐ylmethyleneoxychlorocarbene, 3‐noradamantylme‐thylenoxychlorocarbene, and 1‐adamantylmethylen‐oxychlorocarbene ( 10 ) generated in methanol and dichloroethane by LFP.…”

“…The most extensive studies about various kinds of chlorocarbenes were conducted by Moss et al,93 in the course of which fragmentation patterns and solvation behavior could comprehensively be investigated both experimentally and computationally. Moss et al93 discussed the solvo‐lysis of several alkoxychlorocarbenes, such as 1‐bicyclo[2.2.2]octyloxychlorocarbene, 1‐adamantyl‐oxychlorocarbene ( 9 ), 3‐homoadamantyloxychloro‐carbene, 1‐norbornyloxychlorocarbene, 1‐norborn‐ylmethyleneoxychlorocarbene, 3‐noradamantylme‐thylenoxychlorocarbene, and 1‐adamantylmethylen‐oxychlorocarbene ( 10 ) generated in methanol and dichloroethane by LFP. Ring expansion or direct fragmentation led to the formation of alkonium chloride ion pairs in solution, which could computationally be modeled along with the transition states of molecular fragmentation, employing the B3LYP functional together with the 6‐31G( d ) basis.…”

Homolytic Fragmentation of Allyloxychlorocarbene

“…Photolysis or thermolysis (at 25°C) of diazirine 5 generates allyloxychlorocarbene (1). In polar solvents such as DCE or MeCN, fragmentation of 1 gives allyl chloride (2).…”