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Abstract
Introduction
Protocol
Results
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Chemistry

Isolere gratis Carbenes samt blandede dimere og organiske radikaler

Published: April 19, 2019
doi:
10.3791/59389
, ,
1Department of Chemistry and Pharmacy,Friedrich-Alexander-Universität Erlangen-Nürnberg

Summary

Vi præsenterer protokoller til isolering af stabil Heterocycliske carbenes. Syntesen af et cyklisk (alkyl)(amino) carbene (CAAC) og et N-Heterocycliske carbene (NHC) er påvist ved hjælp af filter cannulas og Schlenk teknik. Desuden præsenterer vi syntesen af de relaterede ilt-følsomme, elektron-rige blandet “Wanzlick dimer” og den reducerede stabile organiske radikaler.

Abstract

Protokoller til isolering af de almindeligt beskæftigede cyklisk (alkyl)(amino) carbene (CAAC) og N-Heterocycliske carbene (NHC) er rapporteret. Desuden, syntesen af deres blandede CAAC – NHC “Wanzlick” dimer og syntesen af de relaterede stabile organisk “olefin” radikale præsenteres. Hovedformålet med dette manuskript er at give et detaljeret og generel protokol til ethvert færdighedsniveau på hvordan man forbereder gratis Heterocycliske carbenes af deprotonation ved hjælp af filteret cannulas syntetisk kemiker. På grund af luft-følsomheden af de syntetiserede forbindelser udføres alle eksperimenter under inert atmosfære ved hjælp af enten Schlenk teknik eller en dinitrogenoxider fyldt handskerum. Styring af Wanzlicks ligevægt (dvs, dimerization gratis carbenes), er en afgørende forudsætning for anvendelsen af gratis carbenes i koordinationskemi eller organisk syntese. Dermed, vi redegøre for de specifikke elektroniske steriske krav og favorisere dannelsen af dimerer, heterodimers eller monomerer. Vi vil vise hvordan proton katalyse tillader dannelsen af dimerer, og hvordan den elektroniske struktur af carbenes og deres dimerer påvirker reaktivitet med enten fugt eller luft. Strukturelle identiteten af de rapporterede forbindelser er drøftet, baseret på deres NMR-spektre.

Introduction

Mere end et halvt århundrede siden, Wanzlick rapporteret velsagtens de første forsøg på at syntetisere N-Heterocycliske carbenes1,2,3. Men i stedet for at isolere den frie carbenes, han lykkedes kun kendetegner deres dimerer. Denne observation fik ham til at foreslå en ligevægt mellem olefin-dimer og de respektive gratis carbenes, som er nu almindeligvis omtales som “Wanzlicks ligevægt” (figur 1, jeg.) 4 , 5 , 6. senere blev det fremført, at dimerization af gratis carbenes og selvfølgelig lige den modsatte reaktion (dvs. dissociation af relaterede olefin dimerer), er katalyseret af protoner7,8,9 ,10,11,12. Det tog en anden 30 år indtil den første “bottleable” carbene, som ikke dimerize ved stuetemperatur, blev rapporteret af Bertrand13,14. Især N-Heterocycliske carbenes (NHCs; imidazolin-2-ylidenes) blev genstand for intensiv forskning efter Arduengo havde rapporteret en stabil krystallinsk NHC, 1,3-diadamantyl-imidazolin-2-ylidene15. Overraskende stabiliteten i dette carbene var første rationaliseret ved en kombination af sterisk virkninger på grund af de omfangsrige adamantyl substituenter samt elektroniske effekter forbundet med den aromatiske N– heterocycle. Men det var vist senere i en elegant undersøgelse af Murphy at selv “monomere” 1,3-dimethyl-imidazolin-2-ylidene16 (dvs. den frie carbene stammer fra N,N– dimethylimidazolium salte) med meget små methyl substituenter er mere stabile end dens dimer17. Lavallo og Bertrand viste tværtimod, at også fjernelse af en stabiliserende nitrogen atom, som rapporteret af isolation af en cyklisk (alkyl)(amino) carbene (CAAC), kan opvejes af indførelsen af en omfangsrig 2,6-diisopropylphenyl (Dipp) erstatningsprodukt 18.

NHCs og CAACs viste sig særdeles frugtbart for koordinationskemi af d – og p-blokelementer, overgangen metal katalyse eller organocatalysis (For temaer og bøger om NHCs, se19,20,21 , 22 , 23, for anmeldelser på CAACs, se24,25,26,27,28, for syntese af CAACs, se18,29, 30 , 31). den imponerende succeshistorie for cyklisk carbene ligander skyldes hovedsagelig to grunde32. Først, både elektroniske og sterisk egenskaber kan indstilles let passer til kravene i en specifik applikation. Andet, isolering af stabil gratis carbenes tilbyder en praktisk metode til at syntetisere metal komplekser af ligetil kombineret med en metal forløber. Derfor er det vigtigt at forstå de faktorer, som kontrollerer om en gratis carbene er stabil på eller under stuetemperatur eller om det dimerizes til at danne en olefin. Bemærk at afledte elektron rige olefiner normalt33 ikke danner komplekser ved behandling med en metal forløber, som er i det mindste delvis på grund af deres stærkt reducerende karakter.

Ikke kun er gratis carbenes nøglespillere i syntetisk kemi i dag. Faktisk er deres elektron rige olefin dimerer34,35,36 (f.eks. tetraazafulvalenes i tilfælde af NHCs37 eller tetrathiafulvalenes TTF38,39,40 i tilfælde af 1,3-dithiol-2-ylidenes; Figur 1, II), har ikke kun fundet bred anvendelse som reduktionsmidler41,42,43, men endnu mere så i økologisk elektronik.

TTF hedder faktisk “mursten-og-mørtel” økologisk elektronik44. Dette er hovedsagelig på grund af de særlige elektroniske egenskaber elektron rige olefiner – især, mange af dem viser tre stabile redox stater ved oxidation, herunder open-shell organiske radikaler (For anmeldelser på carbene afledt organiske radikaler, se:45 ,46,47, for de seneste bidrag i området af carbene stabiliseret organiske radikaler, se:48,49,50,51,52 , 53 , 54). derfor TTF giver mulighed for fremstilling af ledende/semiconductive materiale som krævet for magnetiske materialer, organiske felt – effekten transistorer (OFETs), økologisk light emitting dioder (OLED) og molekylær afbrydere eller sensorer 55,56,57,58,59.

Heri, vi præsenterer praktisk protokoller til isolering af to stabile carbenes med enorme konsekvenser i koordinationskemi og homogen katalyse (figur 2), nemlig den cykliske (alkyl)(amino) carbene 1 18, og den dimethylimidazolin-2-ylidene NHC 2 15. Vi vil diskutere hvorfor både carbenes er stabilt ved stuetemperatur og ikke dimerize. Vi vil derefter udarbejde på proton katalyse relateret til Wanzlicks ligevægt og dannelsen af den blandede CAAC – NHC heterodimer 360,61,62. De spændende elektroniske egenskaber af sådanne triaza-alkener er forbundet med den imponerende stabilitet af relaterede organiske radikale 4 63.

Metodologiske fokus ligger på den Schlenk teknik bruger filter cannulas udstyret med en glas mikro fiber filter til adskillelse af en supernatanten fra et bundfald inert betingelser. En dinitrogenoxider fyldt handskerum bruges til vejning i begyndende materiale og opbevaring af luft følsomme forbindelser.

Protocol

Forsigtig: Udføre alle synteser i et velventileret stinkskab. Slid passende personlige værnemidler (PPE) herunder en laboratoriekittel og sikkerhed goggles. Bemærk: Udgangsmaterialerne blev syntetiseret ifølge litteraturen: 1-(2,6-diisopropylphenyl)-2,2,4,4-tetramethyl-3,4-dihydro-2H- pyrrol-1-ium tetrafluoroborate (1prot) (syntese af CAACs, se:18 ,30,31,…

Representative Results

Gratis carbenes reagerer typisk let med vand66. Derfor, omhyggeligt tørret glasvarer og opløsningsmidler er påkrævet67. I fremgangsmåden ovenfor brugte vi cannulas forsynet med et glas mikro fiber filter for at adskille luft følsomme løsninger fra en bundfaldet inert betingelser. Vi brugte denne teknik til både udvinding af faste stoffer (dvs. den ønskede vare er opløst) samt vask af faste forbindelser (dvs. den ønskede vare er en…

Discussion

Heri, præsenterer vi en generel og fleksibel protokol for syntesen af stabile carbenes (NHC, CAAC) og deres elektron rige dimer. Alle trin kan let være opskaleret til mindst en 25 g skala. Afgørende for en vellykket syntese er de strenge udelukkelser af fugt (luft, henholdsvis) til syntese af carbenes og ilt (luft, henholdsvis) for elektron rige olefin. Heri anvendt filtrering kanyle teknik i kombination med en Schlenk linje er en meget praktisk metode til at adskille løsninger fra bundfald inert betingelser. Filter …

Disclosures

The authors have nothing to disclose.

Acknowledgements

Forfatterne takke Fonds an der Chemischen Industrie for en Liebig fellowship og Hertha og Helmut Schmauser-fonden for økonomisk støtte. Understøttelse af K. Meyer er taknemmeligt anerkendt.

Materials

Equipment
Glass micro fiber filter, 691, 24 mm. Particle retention 1.6 mm VWR 516-0859
magnetic stir bar FengTecEx various
PTFE tape Sigma-Aldrich Z148814-1PAK PTFE tape used in this manuscript was obtained from a local supplier. Tape from Sigma Aldrich should show comparable performance.
rubber septum FengTecEx RS112440 Joint size: 24/29
rubber septum FengTecEx RS111420 Joint size: 14/23
rubber septum FengTecEx RS111922 Joint size: 19/26
schlenk flasks FengTecEx various 100 mL
steel cannula FengtecEx C702024 Attachment of a steel joint by a machine shop not required, but facilitates preparation of filter cannula
syringe cannula FengtecEx S380221
Name Company Catalog Number Comments
Reactants
1-(2,6-diisopropylphenyl)-2,2,4,4-tetramethyl-3,4-dihydro-2H-pyrrol-1-ium tetrafluoroborate Synthesized according to: Jazzar, R., Dewhurst, R. D., Bourg, J. B., Donnadieu, B., Canac, Y., Bertrand, G. Intramolecular “Hydroiminiumation” of alkenes: Application to the synthesis of conjugate acids of cyclic alkyl amino carbenes (CAACs). Angewandte Chemie International Edition 46 (16), 2899-2902, (2007).
1,3-dimethyl-4,5-dihydro-1H-imidazol-3-ium iodide Synthesized according to: Benac, B. L., Burgess, E. M., Arduengo, A. J. 1,3-Dimethylimidazole-2-Thione. Organic Synthesis 64, 92, (1986).
potassium hexamethyldisilazide Sigma-Aldrich 324671-100G CAS 40949-94-8
silver trifluoromethanesulfonate Sigma-Aldrich 85325-25G CAS 2923-28-6
Name Company Catalog Number Comments
Solvents
acetonitrile-D3 Deutero 00202-10m distilled from CaH2, stored over activated molecular sieves
benzene-D6 Deutero 00303-100ml dried over activated molecular sieves, stored over potassium
diethylether – – dried by two-column, solid-state purification system and degassed by three freeze-pump-thaw cycles, stored over activated molecular sieves
hexanes – – dried by two-column, solid-state purification system and degassed by three freeze-pump-thaw cycles, stored over activated molecular sieves
tetrahydrofuran – – dried by two-column, solid-state purification system and degassed by three freeze-pump-thaw cycles, stored over activated molecular sieves
toluene – – dried by two-column, solid-state purification system and degassed by three freeze-pump-thaw cycles, stored over activated molecular sieves
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Schlenk LineAir-sensitive CompoundsCarbenesDimersFree RadicalsFilter CannulaDry And Degassed SolventsIminium SaltKHMDSDinitrogenDiethyl EtherIsopropanol Slush BathPotassium Tetrafluoroborate
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Grünwald, A., Goodner, S. J., Munz, D. Isolating Free Carbenes, their Mixed Dimers and Organic Radicals. J. Vis. Exp. (146), e59389, doi:10.3791/59389 (2019).
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