Highly Selective Room-Temperature Copper-Catalyzed C−N Coupling Reactions

Shafir, Alexandr; Buchwald, Stephen L.

doi:10.1021/ja063063b

Cited by 415 publications

(205 citation statements)

References 9 publications

(8 reference statements)

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“…For the 4-hexyloxyphenyl-substituted phenoxazines, MP12 and MP05, the initial arylation to give 7 followed a procedure reported by Buchwald and coworkers. [52,53] Formylation of 1 and 7 was accomplished by the Vilsmeyer-Haack reaction. Higher yields of 4 and 8 were obtained by heating the reaction mixture to reflux in CHCl 3 overnight, compared to heating in pure dimethylformamide (DMF).…”

Section: Methodsmentioning

confidence: 99%

Phenoxazine Dyes for Dye‐Sensitized Solar Cells: Relationship Between Molecular Structure and Electron Lifetime

Karlsson

Jiang

Eriksson

et al. 2011

Chemistry A European J

108

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A series of metal-free organic dyes with a core phenoxazine chromophore have been synthesized and tested as sensitizers in dye-sensitized solar cells. Overall conversion efficiencies of 6.03-7.40% were reached under standard AM 1.5G illumination at a light intensity of 100 mW cm(-2) . A clear trend in electron lifetime could be seen; a dye with a furan-conjugated linker showed a shorter lifetime relative to dyes with the acceptor group directly attached to the phenoxazine. The addition of an extra donor unit, which bore insulating alkoxyl chains, in the 7-position of the phenoxazine could increase the lifetime even further and, together with additives in the electrolyte to raise the conduction band, an open circuit voltage of 800 mV could be achieved. From photoelectron spectroscopy and X-ray absorption spectroscopy of the dyes adsorbed on TiO(2) particles, it can be concluded that the excitation is mainly of cyano character (i.e., on average, the dye molecules are standing on, and pointing out, from the surface of TiO(2) particles).

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Section: Methodsmentioning

confidence: 99%

Phenoxazine Dyes for Dye‐Sensitized Solar Cells: Relationship Between Molecular Structure and Electron Lifetime

Karlsson

Jiang

Eriksson

et al. 2011

Chemistry A European J

108

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“…[5][6][7][8][13][14][15][16] Warren's group 8 has isolated a Ni( -diketiminate)nitrene complex that can effect C-H activation of 1,4-cyclohexadiene (CD-H). Amination by late metal catalysts (notably Pd 17 and Cu 18 ) is established in organic synthesis but involves initial functionalization of a hydrocarbon to produce a more reactive surrogate (e.g., organic chloride). Direct amination of hydrocarbons is more desirable from an atomeconomical viewpoint.…”

Section: Introductionmentioning

confidence: 99%

Catalytic Tuning of a Phosphinoethane Ligand for Enhanced C−H Activation

et al. 2008

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Hydrogen atom abstraction (HAA) from 1,4-cyclohexadiene (CD-H) by (dtbpe)Ni(NAr) to form a Ni I -amide, (dtbpe)Ni(NHAr), and cyclohexadienyl radical is calculated to be thermodynamically reasonable, ∆H HAA(dtbpe) ) -1.3 kcal/mol, dtbpe ) bis(di-tert-butylphosphino)ethane, Ar ) 2,6-diisopropylphenyl. However, radical rebound to form a metal-bound amine is highly endothermic (∆H reb(dtbpe) ) +25.1 kcal/ mol). Analysis of bond enthalpies indicates that weakening of the Ni-N bond (Ni-amide f Ni-amine) upon radical rebound is not compensated by the weak C-N bond formed. Hence, a ligand was sought that would enhance the metal-amine bond strength while diminishing the metal-amide bond strength. Reaction of (dfmpe)Ni(NAr) with CD-H was thus analyzed, dfmpe ) bis(di(trifluoromethyl)phosphino)ethane. While there is a small change in the thermodynamics of HAA (∆H HAA(dfmpe) ) -5.7 kcal/mol), there is a profound change in the rebound step (∆H reb(dfmpe) ) -7.8 kcal/mol) upon replacing dtbpe by dfmpe. Regeneration of the nitrene active species by reaction of ArN 3 with the metal-bound product is calculated to be highly exothermic, ∆H reg ) -36.7 kcal/mol. Two candidates for a precatalyst, (dfmpe)Ni(COD) and (dfmpe)Ni(bpy), COD ) 1,5-cyclooctadiene and bpy ) 2,2′-bipyridine, were calculated to undergo highly exothermic reactions with ArN 3 to form the nitrene active species. The calculated enthalpic barrier for HAA of CD-H by (dfmpe)Ni(NAr) is 21.3 kcal/mol. Hence, consideration of the computed thermodynamics and kinetics suggests that nickel-nitrenes with fluorinated phosphine supporting ligation are promising candidates for catalytic amination of C-H bonds.

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“…Therefore, it is desirable to develop milder copper-catalyzed coupling methods. Recently, Shafir and Buchwald [9] and ourselves [10] have developed copper-catalyzed N-arylations at room temperature, and the results showed that the efficiency of the copper-catalyzed coupling reactions was highly dependent on the involvement of suitable ligands. To the best of our knowledge, there is no example of constructing N-heterocycles under ligand-free copper catalysis at room temperature.…”

mentioning

confidence: 99%