Pyridine ylide formation by capture of phenylchlorocarbene and tert-butylchlorocarbene. Reaction rates of an alkylchlorocarbene by laser flash photolysis

Jackson, James E.; Soundararajan, Ν.; Platz, Matthew S.; Liu, Michael T. H.

doi:10.1021/ja00224a068

Cited by 160 publications

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“…These two mutually independent probes strongly suggest selective activation of the C5-H bond during silver carbene complex formation. Chemoselective C5-H bond activation seems to be governed by electronic factors, in particular imparted by the electron-withdrawing impact of the fused pyridine system, which activates the α-position as typical in classical N-ylide chemistry [55][56][57][58]. Steric factors seem much less relevant, due partly to the linear coordination geometry assumed for the silver carbene intermediate [59], and also due to the small size of the methyl substituents at nitrogen.…”

Section: Resultsmentioning

confidence: 99%

Iridium, ruthenium, and palladium complexes containing a mesoionic fused imidazolylidene ligand

Petronilho

Müeller-Bunz

Albrecht

2015

Journal of Organometallic Chemistry

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Imidazo[1,2-a]pyridine consisting of a pyridine fused to an imidazolium salt at the imidazolium N1-C2 bond and hence protected from forming normal imidazole-2-ylidene complexes undergoes selective activation of the C5-H bond with Ag 2 O, i.e. at the imidazolium carbon that is proximal to the pyridine nitrogen. While the silver carbene complex is unstable, transmetallation with [IrCp*Cl 2 ] 2 , [RuCl 2 (cym)] 2 , and [PdCl(allyl)] 2 afforded stable mesoionic carbene complexes. Two iridium(III) complexes containing one fused carbene ligand and one palladium(II) complex containing two carbene ligands at the metal center were structurally characterized. The absence of substituents adjacent to the carbene carbon prevents wingtip group activation, and it imparts a reduced stability of the complexes in particular under (mildly) acidic conditions.

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Section: Resultsmentioning

confidence: 99%

Iridium, ruthenium, and palladium complexes containing a mesoionic fused imidazolylidene ligand

Petronilho

Müeller-Bunz

Albrecht

2015

Journal of Organometallic Chemistry

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“…The observed rate constants, k obs are summarized in Table 1, where the activation energy (E a ), activation enthalpy (∆H ‡ ) and activation Gibbs free energy (∆G ‡ ) are also shown. Generally, the activation enthalpy for decomposition reaction of aryl diazo compounds is known as 3-4 kcal/mol 13 and the activation energy of the essentially diffusioncontrolled reaction is 2-3 kcal/mol. 13 The latter value is only an apparent activation energy which results from the decrease in k diff at low temperature due to increased solvent viscosity.…”

Section: Resultsmentioning

confidence: 99%

“…11 Generally, alkylcarbenes give ylide intermediates, 7 in their trapping compounds as acetonitrile or pyridine. [12][13][14][15][16][17] Although many alkylketocarbene reactions with acetonitrile or pyridine quenchers have been studied, the ylide intermediates involving arylketocarbene with acetonitrile or pyridine have not yet reported.…”

Section: Introductionmentioning

confidence: 99%

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Interconversion of Electronic Spin State of p-Substituted Arylketocarbene Reactions

2004

Bulletin of the Korean Chemical Society

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Rate constants for photolytic reactions of p-substituted 2-diazopropiophenones were determined in acetonitrile. The reactions show a comparatively low value of activation energy and activation enthalpy to alkylcarbenes or other arylcarbenes. The transition state corresponds to the step of a new carbonyl bond formation. The high negative ρ-values are shown in Hammett plots. The kinetics results and EPR spectrum are in accord with a phenomenon that occurs in interconversion between singlet and triplet carbenes.

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“…18,19 In need of a clear spectral window, we thus measured the rate of formation of the pyridine ylide 20,21 of PhCCl at 460 nm at varying concentrations of 3a.…”

Section: ■ Introductionmentioning

confidence: 99%

Experimental and Computational Mechanistic Investigation of Chlorocarbene Additions to Bridgehead Carbene–Anti-Bredt Systems: Noradamantylcarbene–Adamantene and Adamantylcarbene–Homoadamantene

et al. 2015

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Cophotolysis of noradamantyldiazirine with the phenanthride precursor of dichlorocarbene or phenylchlorodiazirine in pentane at room temperature produces noradamantylethylenes in 11% yield with slight diastereoselectivity. Cophotolysis of adamantyldiazirine with phenylchlorodiazirine in pentane at room temperature generates adamantylethylenes in 6% yield with no diastereoselectivity. (1)H NMR showed the reaction of noradamantyldiazirine + phenylchlorodiazirine to be independent of solvent, and the rate of noradamantyldiazirine consumption correlated with the rate of ethylene formation. Laser flash photolysis showed that reaction of phenylchlorocarbene + adamantene was independent of adamantene concentration. The reaction of phenylchlorocarbene + homoadamantene produces the ethylene products with k = 9.6 × 10(5) M(-1) s(-1). Calculations at the UB3LYP/6-31+G(d,p) and UM062X/6-31+G(d,p)//UB3LYP/6-31+G(d,p) levels show the formation of exocyclic ethylenes to proceed (a) on the singlet surface via stepwise addition of phenylchlorocarbene (PhCCl) to bridgehead alkenes adamantene and homoadamantene, respectively, producing an intermediate singlet diradical in each case, or (b) via addition of PhCCl to the diazo analogues of noradamantyl- and adamantyldiazirine. Preliminary direct dynamics calculations on adamantene + PhCCl show a high degree of recrossing (68%), indicative of a flat transition state surface. Overall, 9% of the total trajectories formed noradamantylethylene product, each proceeding via the computed singlet diradical.

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Pyridine ylide formation by capture of phenylchlorocarbene and tert-butylchlorocarbene. Reaction rates of an alkylchlorocarbene by laser flash photolysis

Cited by 160 publications

References 0 publications

Iridium, ruthenium, and palladium complexes containing a mesoionic fused imidazolylidene ligand

Iridium, ruthenium, and palladium complexes containing a mesoionic fused imidazolylidene ligand

Interconversion of Electronic Spin State of p-Substituted Arylketocarbene Reactions

Experimental and Computational Mechanistic Investigation of Chlorocarbene Additions to Bridgehead Carbene–Anti-Bredt Systems: Noradamantylcarbene–Adamantene and Adamantylcarbene–Homoadamantene

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