Very Strong Organosuperbases Formed by Combining Imidazole and Guanidine Bases: Synthesis, Structure, and Basicity

Vazdar, Katarina; Kunetskiy, Roman A.; Saame, Jaan; Kaupmees, Karl; Leito, Ivo; Jahn, Ullrich

doi:10.1002/anie.201307212

Cited by 70 publications

(58 citation statements)

References 39 publications

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“…The GB values of all considered conformers for compounds 1-3 are compared in Table 2. The modelled 3Et-c2 and 3Pr-c1 guanidines, with their GB values above 1155 kJ mol −1 belong to the most basic neutral non-phosphorus all-guanidine bases and their gas-phase basicity is comparable to recently published bis-imidazolydene guanidine derivatives 20 and aforementioned bis-TBD. 7 Together with the analogues bearing 4-dimethylaminopyridine 21 or TMG subunit, achieved.…”

Section: Gas-phase Basicitysupporting

confidence: 61%

The Utility of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as a Hydrogen Bond Acceptor in the Design of Novel Superbasic Guanidines – A Computational Study

Štrukil¹,

Antol²,

Glasovac³

2014

Croat. Chem. Acta

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Abstract. New guanidine-derived superbases with TBD-functionalized alkyl side chains have been developed using a computational DFT approach. Exploiting the high hydrogen bond basicity of TBD allowed access to systems with strong charge-assisted intramolecular hydrogen bonds in the protonated state. The enhanced stability of such guanidines is mirrored in their gas-phase basicities, which cover the range from 1044−1168 kJ mol −1 , depending on the number of alkyl side chains, the type of alkyl spacer and the hydrogen-bonding pattern.

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Section: Gas-phase Basicitysupporting

confidence: 61%

The Utility of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as a Hydrogen Bond Acceptor in the Design of Novel Superbasic Guanidines – A Computational Study

Štrukil¹,

Antol²,

Glasovac³

2014

Croat. Chem. Acta

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“…Interestingly,the tBu-N = P n (dma) system has the best fit (RMSD = 0.1) of all the investigated systems, and one of the lowest k values.T he excellent fit indirectly supports the high quality of the MeCN pK a values,w hich is remarkable,since the pK a values of the higher members of the series have been obtained by extrapolation from data in THF. Possible examples can be seen for example in the recently reported BIG bases [11] and cyclopropenimine bases. [5] Thep roposed quantitative model for predicting basicity increase resulting from expanding the molecular framework demonstrates that the GB region around 350 kcal mol À1 and beyond is well reachable with non-chelating organosuperbases.Since high-molecular-weight bases are inconvenient in practical use (owing to the large amount of base required), the real challenge in superbase design lies not in the highest possible basicity at any cost but rather in finding structural units that are both efficient in increasing basicity and being smaller.…”

mentioning

confidence: 98%

“…[4,5] Design and synthesis of new superbases has been aflourishing field of research during the last decades. [1,4] Numerous families of superbases (such as phosphazenes, [3] phosphatranes, [6] bisphosphazene proton sponges, [7,8] imidazolidines, [9] imidazolidino-phosphazenes [10] and -guanidines, [11] bis-guanidines [12] )h ave been created and potentially superbasic compound families have been proposed, for example carbenes. [13] More recently different innovative bases have been proposed, such as cyclopropeneimines [14] and silylene bases.…”

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confidence: 99%

Basicity Limits of Neutral Organic Superbases

Leito

Koppel

et al. 2015

Angewandte Chemie

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The potential limits of superbasicity achievable with different families of neutral bases by expanding the molecular framework are explored using DFT computations.Anumber of different core structures of non-ionic organosuperbases are considered (such as phosphazenes,g uanidinophosphazenes, guanidino phosphorus ylides). As imple model for describing the dependence of basicity on the extent of the molecular framework is proposed, validated, and used for quantitatively predicting the ultimate basicities of different compound families and the rates of substituent effect saturation. Some of the considered bases (guanidino phosphorus carbenes) are expected to reach gas-phase basicity around 370 kcal mol À1 , thus being the most basic neutral bases ever reported. Also,the classical substituted alkylphosphazenes were predicted to reach pK a values of around 50 in acetonitrile,w hich is significantly higher than previously expected.Non-ionic organosuperbases [1] are attracting significant interest because of their practical importance as catalysts [1,2] and auxiliary reagents [3] in synthesis and technology as well as for fundamental challenges. [4,5] Design and synthesis of new superbases has been aflourishing field of research during the last decades. [1,4] Numerous families of superbases (such as phosphazenes, [3] phosphatranes, [6] bisphosphazene proton sponges, [7,8] imidazolidines, [9] imidazolidino-phosphazenes [10] and -guanidines, [11] bis-guanidines [12] )h ave been created and potentially superbasic compound families have been proposed, for example carbenes. [13] More recently different innovative bases have been proposed, such as cyclopropeneimines [14] and silylene bases. [15] Despite av ast range of potential applications, [1] many classes of superbases (guanidino proton sponges, [7] phosphorus ylides [16] )a re still almost unexplored.An early Minireview by Schwesinger [17] summarizes the principal approaches to enhancing the basicity of organosuperbases:1 )the "battery cell" principle, [3] that is,s tepwise expansion of the molecular scaffold by forming alternating formal single and double bonds and thereby enhancing the structure where the positive charge can be delocalized (Scheme 1);2 )stabilization of the protonated form by intramolecular hydrogen bond (chelation);a nd 3) structures that become aromatic on protonation. It was concluded that the most fruitful approach to design of superbases is the battery cell principle.T he best known practical example is the phosphazene family of superbases. [3] Creating as tructure where the protonated form is stabilized by one or more hydrogen bonds is also frequently used [4,7,8] and often remarkable basicity enhancement is seen, especially in the gas phase.H owever,i np ractical usage,n ot only thermodynamic but also kinetic basicity is important and here is the drawback of the chelating bases,a st hey generally are kinetically slow. [7] In this work, we computationally explore (DFT B3LYP 6-311 + G** and DFT BP TZVP) five families of potentially extreme...

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“…[6] Yang recently showed that proazaphosphatranes (also knowna sV erkade'ss uperbases) [7] have comparable TEP values to P(tBu) 3 (Figure 1). [8] Amongt he varioust ypes of nonionic superbases, [9] proazaphosphatranes are unique because they become protonated at the phosphorus atom. [7] Hence, they were not only used as ligands in transition-metal-catalyzed transformations, [10] but more importantly found broad applications as stoichiometricb ases and as catalysts in organic synthesis.…”

mentioning

confidence: 99%

Tris(imidazolin‐2‐ylidenamino)phosphine: A Crystalline Phosphorus(III) Superbase That Splits Carbon Dioxide

Mehlmann

Mück‐Lichtenfeld

Tan

et al. 2016

Chemistry A European J

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We report the synthesis and remarkable properties of the phosphine P(NIiPr) (NIiPr=1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidenamino), a crystalline solid accessible through a short and scalable route. Evaluation of the electron-donor properties reveals a Tolman electronic parameter (TEP) value of 2029.7 cm for the new phosphine that is significantly lower than those of all known phosphines or even N-heterocyclic carbenes. Moreover, P(NIiPr) is more basic [pK (MeCN)=38.8] than Verkade's proazaphosphatranes, thus being the strongest reported nonionic phosphorus(III) superbase. The coordination chemistry of the new phosphine towards different metal centers has been explored, and due to its unique electron-releasing character, the phosphine is capable of capturing and cleaving the CO molecule.

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Very Strong Organosuperbases Formed by Combining Imidazole and Guanidine Bases: Synthesis, Structure, and Basicity

Cited by 70 publications

References 39 publications

The Utility of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as a Hydrogen Bond Acceptor in the Design of Novel Superbasic Guanidines – A Computational Study

The Utility of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as a Hydrogen Bond Acceptor in the Design of Novel Superbasic Guanidines – A Computational Study

Basicity Limits of Neutral Organic Superbases

Tris(imidazolin‐2‐ylidenamino)phosphine: A Crystalline Phosphorus(III) Superbase That Splits Carbon Dioxide

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