Time resolved spectroscopy of carbenepyridene ylides: Distinguishing carbenes from diazirine excited states

Platz, Matthew S.; White, W. R.; Modarelli, David A.; Celebi, S.

doi:10.1163/156856794x00180

Cited by 28 publications

(18 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In addition, the carbonyl oxygen could have acted as an election donor, reacting with a carbene to initially form an ylide which could react further to afford secondary products. 15,16 UV-visible spectroscopic analysis of the crude product mixtures obtained from photochemical reaction of the fluorenone 1 with acetic acid, nbutylamine and N-butylbutyramide exhibited strong adsorption maxima at 277 nm (in 2,2,2-trichloroethanol) corresponding to the fluorenone moiety.…”

Section: Photochemisty Of Diazirine Functionalised Fluorenonementioning

confidence: 99%

Surface modification of nylon 6,6 using a carbene insertion approach

2006

View full text Add to dashboard Cite

Section: Photochemisty Of Diazirine Functionalised Fluorenonementioning

confidence: 99%

Surface modification of nylon 6,6 using a carbene insertion approach

2006

View full text Add to dashboard Cite

“…Such 1,2-shifts have been demonstrated repeatedly for nitrogenous carbene precursors that are subject to 1,2 hydrogen shifts or carbon shifts to relieve ring strain. [4][5][6][7][8][9][10] We 11-13 and others [14][15][16][17][18] have shown in previous work that photolysis of dibenzothiophene-S-oxide and its derivatives leads to chemistry that appears to derive from S-O cleavage and formation of atomic oxygen. Although direct evidence for this mechanism in the form of spectroscopic detection of O( 3 P) is lacking, we have recently shown through time-resolved IR experiments that benzoyl nitrene is formed on photolysis of N-benzoyl dibenzothiophene sulfilimine.…”

mentioning

confidence: 95%

S,C-Sulfonium Ylides from Thiophenes: Potential Carbene Precursors

2007

View full text Add to dashboard Cite

Carbenes remain important and intriguing reactive intermediates in organic chemistry despite years of study for many reasons, among them the access they provide to unusual product compounds, their differing chemistry depending on spin state, and their mechanistic complexity. Photochemical precursors to carbenes, such as diazo compounds and diazirines, are often favored, because they can yield carbenes by photolysis at low temperatures and can be used for laser flash photolysis experiments. However, because these nitrogenous precursors have been shown to undergo reactions in their excited states that mimic chemistry expected from the carbene itself, there is demand for alternative practical precursors. In this Communication, we report the use of S,C-sulfonium ylides 1-4 as photochemical carbene precursors, as illustrated in Scheme 1 for compound 4.The choice of compounds 1-4 as potential precursors to dicarbomethoxycarbene for this study was driven by two considerations. First S,C-ylides of malonates are known to be stable and easy to prepare, at least in part because of the electron withdrawing groups that delocalize the formal negative charge. Second, by generating dicarbomethoxycarbene 1-3 for the proof-of-concept work of showing carbene generation, we believed we could distinguish between reactions of the carbene and a potential excited state Wolfflike rearrangement that might yield a ketene derivative. Such 1,2shifts have been demonstrated repeatedly for nitrogenous carbene precursors that are subject to 1,2 hydrogen shifts or carbon shifts to relieve ring strain. [4][5][6][7][8][9][10]

show abstract

“…One of the most intriguing of these intermediates are carbenes. Discovered over 100 years ago , and systematically studied since about 1950, − their investigation is still a field of much current interest. − The most simple carbene, methylene, is a ground-state triplet with a singlet-triplet splitting (S/T) of 9.05 kcal/mol …”

Section: Introductionmentioning

confidence: 99%

Hydrogen Migration vs Carbon Migration in Dialkylcarbenes. A Study of the Preferred Product in the Carbene Rearrangements of Ethylmethylcarbene, Cyclobutylidene, 2-Norbornylidene, and 2-Bicyclo[2.1.1]hexylidene

et al. 1997

View full text Add to dashboard Cite

Ethylmethylcarbene (1), cyclobutylidene (2), 2-norbornylidene (3), and 2-bicyclo[2.1.1]-hexylidene (4) and the transition states that correspond to 1,2-H-migration, 1,3-H-migration, and 1,2-C-migration were optimized at BHandHLYP/DZP, MP2/DZP, and CCSD(T)/DZP levels of theory. The 1,2-H-migration of 1 to 2-butene has a theoretically derived barrier of 5.2 kcal/mol at CCSD(T)/DZP. The 1,2-H-shift that leads to 1-butene has a ΔG ⧧ of 8.5 kcal/mol, 1,3-H-migration of 8.3 kcal/mol and 1,2-C-migration of 18.1 kcal/mol. For 2 ΔG ⧧ for 1,2-C-migration is only 10.5 kcal/mol, which is 7.6 kcal/mol less than for 1. This lowering of the barrier for rearrangment of cyclobutylidene is attributed to the similarity between the TS and singlet 2 which prefers a nonclassical structure. The barrier for 1,2-H-migration for 2 is 9.7 kcal/mol due to H repulsion in the TS. For 3 the process with the lowest barrier (5.2 kcal/mol, BHandHLYP/DZP) is a 1,3-H-shift that leads to nortricyclene. The preference for this rearrangement can again be explained by the similarity between the carbene geometry and that of the corresponding TS that leads to the nortricyclene. For the rearrangement of 4, which also resembles the TS for 1,3-H-migration, the corresponding TS has a ΔG ⧧ of 22.6 kcal/mol (BHandHLYP/DZP). The reason for this diverging behavior is the large amount of ring strain present in the TS for 1,3-H-migration of 4. As a consequence, 4 is a long-lived, trappable carbene that rearranges slowly to form bicyclo[2.1.1]hex-2-ene (ΔG ⧧ = 16.2 kcal/mol), while 3 can not be trapped with pyridine.

show abstract

Time resolved spectroscopy of carbenepyridene ylides: Distinguishing carbenes from diazirine excited states

Cited by 28 publications

References 33 publications

Surface modification of nylon 6,6 using a carbene insertion approach

Surface modification of nylon 6,6 using a carbene insertion approach

S,C-Sulfonium Ylides from Thiophenes: Potential Carbene Precursors

Hydrogen Migration vs Carbon Migration in Dialkylcarbenes. A Study of the Preferred Product in the Carbene Rearrangements of Ethylmethylcarbene, Cyclobutylidene, 2-Norbornylidene, and 2-Bicyclo[2.1.1]hexylidene

Contact Info

Product

Resources

About