A comparative DFT study of TBD-catalyzed reactions of amines with CO<sub>2</sub> and hydrosilane: the effect of solvent polarity on the mechanistic preference and the origins of chemoselectivities

Zhang, Chaoshen; Lu, Yu; Zhao, Ruihua; Menberu, Wasihun; Guo, Jiandong; Wang, Zhixiang

doi:10.1039/c8cc05788e

Cited by 31 publications

(44 citation statements)

References 19 publications

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“…7.5 can be attributed to the differencei n BEs and ion pairing (vide supra) and to varying degree of catalyst inhibition by the reversibleb inding of the anion to the hydrosilane. 7.5 in DMSO irrespective of the structure of the anion.I na ddition, the stability of the carbamate salts are furthere nhanced by polar solvents, [48] which can also partly explain the differences among the solvent free reactions and reactions carriedo ut in MeCN, DMF and DMSO. acting as an ucleophile) (Figure 4, TS1).…”

Section: Resultsmentioning

confidence: 99%

“…From the activity‐p K a trend recorded here, it would appear that for N‐ methylaniline, a catalyst with p K a values >4.0 is required for the carbamate salt stabilization, with maximum stabilization reached for all TBA + salts with p K a values ≥7.5 in DMSO irrespective of the structure of the anion. In addition, the stability of the carbamate salts are further enhanced by polar solvents, which can also partly explain the differences among the solvent free reactions and reactions carried out in MeCN, DMF and DMSO. However, since carbamate salt formation is predominantly dependent on the amine used the observed trend with N‐ methylaniline does not directly apply to other amines.…”

Section: Resultsmentioning

confidence: 99%

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Delineation of the Critical Parameters of Salt Catalysts in the N‐Formylation of Amines with CO₂

Hulla

Ortiz

Katsyuba

et al. 2019

Chemistry A European J

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N-formylation of amines combining CO 2 as aC 1 source with ah ydrosilane reducing agent is ac onvenient route for the synthesis of N-formylated compounds. Al arge number of salts including ionic liquids( ILs) have been shown to efficientlyc atalyzet he reaction and, yet, the key features of the catalystr emain unclear and the best salt catalysts for the reactionr emainu nknown. Here we demonstrate the detrimental effect of ion pairing on the catalytic activity andi llustrate ways in which the strength of the in-teraction between the ions can be reduced to enhanceinteractions and, hence, reactivity with the substrates. In contrast to the current hypothesis, we also show that salt catalysts are more active as bases rather than nucleophilesand identify the pKaw here the nucleophilic role of the catalyst switches to the more active basic role. The identification of these critical parameters allows the optimum salt catalyst and conditions for an N-formylation reaction to be predicted.Scheme1.N-Formylation of amines with CO 2 and hydrosilane reducing agents.[a] M.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Delineation of the Critical Parameters of Salt Catalysts in the N‐Formylation of Amines with CO₂

Hulla

Ortiz

Katsyuba

et al. 2019

Chemistry A European J

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“…Chemie and the amine. [31] Not only does the carbamate salt of the amine act as the CO 2 reduction catalyst, it also catalyzes the subsequent reduction to silylacetal. More nucleophilic amines also react faster with formoxysilane to form formamides.…”

Section: Methodsmentioning

confidence: 99%

“…Nevertheless,acetylboranes,the equivalent of silylacetals in hydroborane reductions,h ave been observed in CO 2 reduction to methanol with 9-BBN. [62] Considering that all the reduction reactions are catalyzed by base stabilized carbamate salts in the form [BaseH]-[RR'NCOO], [15,17,31] which activate the hydrosilane reducing agent by nucleophilic attack, all bases of sufficient strength should catalyze all three reactions.T he alternative hydrosilane activation by insufficiently basic nucleophiles is less favored. [39] Only 1,3,2-diazaphospholene [53,54] and B(C 6 F 5 ) 3 [59] appear to have adifferent catalytic role.…”

Section: Formamides N-methylamines or Aminalsmentioning

confidence: 99%

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Pivotal Role of the Basic Character of Organic and Salt Catalysts in C−N Bond Forming Reactions of Amines with CO₂

Hulla

Dyson

2019

Angew Chem Int Ed

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Organocatalysts promote a range of C−N bond forming reactions of amines with CO2. Herein, we review these reactions and attempt to identify the unifying features of the catalysts that allows them to promote a multitude of seemingly unrelated reactions. Analysis of the literature shows that these reactions predominantly proceed by carbamate salt formation in the form [BaseH][RR′NCOO]. The anion of the carbamate salt acts as a nucleophile in hydrosilane reductions of CO2, internal cyclization reactions or after dehydration as an electrophile in the synthesis of urea derivatives. The reactions are enhanced by polar aprotic solvents and can be either promoted or hindered by H‐bonding interactions. The predominant role of all types of organic and salt catalysts (including ionic liquids, ILs) is the stabilization of the carbamate salt, mostly by acting as a base. Catalytic enhancement depends on the combination of the amine, the base strength, the solvent, steric factors, ion pairing and H‐bonding. A linear relationship between the base strength and the reaction yield has been demonstrated with IL catalysts in the synthesis of formamides and quinazoline‐2,4‐diones. The role of organocatalysts in the reactions indicates that all bases of sufficient strength should be able to catalyze the reactions. However, a physical limit to the extent of a purely base catalyzed reaction mechanism should exist, which needs to be identified, understood and overcome by synergistic or alternative methods.

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Iron‐Catalyzed Selective N‐Methylation and N‐Formylation of Amines with CO₂

Zhu

et al. 2019

Adv Synth Catal

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We herein describe an efficient iron‐catalyzed selective N‐methylation and N‐formylation of amines with CO2 and silane using mono‐phosphine as ligand. With commercially available [CpFe(CO)2]2 as catalyst, Fe‐catalyzed methylation of amines was achieved with triphenylphosphine as a ligand. Using tributylphosphine as a ligand, Fe‐catalyzed formylation of amines was realized at a lower temperature. The method was successfully applied in the late‐stage methylation and formylation of drug molecules containing amine moiety.magnified image

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A comparative DFT study of TBD-catalyzed reactions of amines with CO₂ and hydrosilane: the effect of solvent polarity on the mechanistic preference and the origins of chemoselectivities

Cited by 31 publications

References 19 publications

Delineation of the Critical Parameters of Salt Catalysts in the N‐Formylation of Amines with CO₂

Delineation of the Critical Parameters of Salt Catalysts in the N‐Formylation of Amines with CO₂

Pivotal Role of the Basic Character of Organic and Salt Catalysts in C−N Bond Forming Reactions of Amines with CO₂

Iron‐Catalyzed Selective N‐Methylation and N‐Formylation of Amines with CO₂

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A comparative DFT study of TBD-catalyzed reactions of amines with CO2 and hydrosilane: the effect of solvent polarity on the mechanistic preference and the origins of chemoselectivities

Cited by 31 publications

References 19 publications

Delineation of the Critical Parameters of Salt Catalysts in the N‐Formylation of Amines with CO2

Delineation of the Critical Parameters of Salt Catalysts in the N‐Formylation of Amines with CO2

Pivotal Role of the Basic Character of Organic and Salt Catalysts in C−N Bond Forming Reactions of Amines with CO2

Iron‐Catalyzed Selective N‐Methylation and N‐Formylation of Amines with CO2

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A comparative DFT study of TBD-catalyzed reactions of amines with CO₂ and hydrosilane: the effect of solvent polarity on the mechanistic preference and the origins of chemoselectivities

Delineation of the Critical Parameters of Salt Catalysts in the N‐Formylation of Amines with CO₂

Delineation of the Critical Parameters of Salt Catalysts in the N‐Formylation of Amines with CO₂

Pivotal Role of the Basic Character of Organic and Salt Catalysts in C−N Bond Forming Reactions of Amines with CO₂

Iron‐Catalyzed Selective N‐Methylation and N‐Formylation of Amines with CO₂