Exceptional Superbasicity of Bis(guanidine) Proton Sponges Imposed by the Bis(secododecahedrane) Molecular Scaffold: A Computational Study

Margetić, Davor; Ishikawa, Tsutomu; Kumamoto, Takuya

doi:10.1002/ejoc.201000828

Cited by 34 publications

(30 citation statements)

References 47 publications

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“…5 Design and synthesis of new superbases has been a flourishing 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‐phosphazenes10 and ‐guanidines,11 bis‐guanidines12) have been created and potentially superbasic compound families have been proposed, for example carbenes 13. More recently different innovative bases have been proposed, such as cyclopropeneimines14 and silylene bases 15.…”

Section: Methodsmentioning

confidence: 99%

Basicity Limits of Neutral Organic Superbases

Leito

Koppel

et al. 2015

Angew Chem Int Ed

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Section: Methodsmentioning

confidence: 99%

Basicity Limits of Neutral Organic Superbases

Leito

Koppel

et al. 2015

Angew Chem Int Ed

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“…[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.…”

mentioning

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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“…The calculated results show that the most basic carbene 5 exhibits a pK a of 51.5 and has been found to be (40−46.9) of known superbases. 11,12,17,18,20 The second pK a value is reported for the designed superbases up to 50.1, which is the highest second pK a reported to date. The calculated second pK a values calculated for 6−8 are comparable to the first pK a values due to the greater stabilization of the bis-cationic form of carbenes in the solvent medium compared to the corresponding neutral and monocationic forms.…”

Section: Resultsmentioning

confidence: 84%

In Silico Studies in Exploiting Weak Noncovalent C–H⁺···π and π–π Interactions To Achieve Dual Properties: Hyperbasicity and Multiple Dihydrogen Storage Materials with Paracyclophane-Based Carbene Derivatives

Ganguly

2013

J. Phys. Chem. C

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This work reports that noncovalent interactions can be exploited to achieve hyperbasicity of a base. A new class of superbase has been identified using paracyclophane-based carbenes that possess a proton affinity (PA) value of 1251.4 kJ/mol at the M06-2X/6-311+G**//B3LYP/6-31+G* level of theory. Noncovalent interactions such as C−H + ···π and through-space π−π interactions amplify the basicity of such carbene systems by the stabilization of their protonated forms. These paracyclophane systems can be a suitable candidate for bis-protonation with the highest pK a (MeCN) value of 50.1 to date. The side phenyl ring in paracyclophane systems that is not directly involved in C−H + ···π type interactions contributes to augment the basicity by throughspace π−π interactions. The side ring of the paracyclophane system is involved in enhancement of the proton affinity of 19.3 kJ/mol via through-space π−π interaction. Molecular electrostatic potential (MESP) analysis shows that such noncovalent interactions can enhance the electron density at the reactive sites in suitably designed systems. The absolute minima of the MESP (V min ) located for these carbene systems correlate well with their calculated proton affinity values. The frontier molecular orbital energy differences (HOMO−LUMO) of such carbenes also correlate well with their proton affinity results. These paracyclophane-based carbene systems can be used for selective binding of lithium ions. Such lithium decorated systems can be exploited as a molecular container for the storage of multiple dihydrogen. This is the first example of the use of lithiated organic superbases as hydrogen storage material. The calculated conceptual density functional theory-based reactivity descriptors such as electronegativity, hardness, and electrophilicity indicate the stability of these H 2 trapped molecules. The calculated desorption energies per H 2 molecule (ΔE DE ) also indicate the recyclable property of the hydrogen storage materials.

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Exceptional Superbasicity of Bis(guanidine) Proton Sponges Imposed by the Bis(secododecahedrane) Molecular Scaffold: A Computational Study

Cited by 34 publications

References 47 publications

Basicity Limits of Neutral Organic Superbases

Basicity Limits of Neutral Organic Superbases

Basicity Limits of Neutral Organic Superbases

In Silico Studies in Exploiting Weak Noncovalent C–H⁺···π and π–π Interactions To Achieve Dual Properties: Hyperbasicity and Multiple Dihydrogen Storage Materials with Paracyclophane-Based Carbene Derivatives

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Exceptional Superbasicity of Bis(guanidine) Proton Sponges Imposed by the Bis(secododecahedrane) Molecular Scaffold: A Computational Study

Cited by 34 publications

References 47 publications

Basicity Limits of Neutral Organic Superbases

Basicity Limits of Neutral Organic Superbases

Basicity Limits of Neutral Organic Superbases

In Silico Studies in Exploiting Weak Noncovalent C–H+···π and π–π Interactions To Achieve Dual Properties: Hyperbasicity and Multiple Dihydrogen Storage Materials with Paracyclophane-Based Carbene Derivatives

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In Silico Studies in Exploiting Weak Noncovalent C–H⁺···π and π–π Interactions To Achieve Dual Properties: Hyperbasicity and Multiple Dihydrogen Storage Materials with Paracyclophane-Based Carbene Derivatives