Perspectives

Ishikawa, Tsutomu; Margetić, Davor

doi:10.1002/9780470740859.ch11

Cited by 3 publications

(4 citation statements)

References 20 publications

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“…Neutral organic bases are compounds extensively used as catalysts in synthetic organic chemistry, due to their ability to initiate a reaction by spontaneous deprotonation of reagents. 1 The important advantages of neutral organic bases over their ionic inorganic counterparts are much better solubility in organic solvents and milder reaction conditions. Organic compounds that are more basic than the proton sponge 1,8-bis(dimethylamino)naphthalene (DMAN), with a proton affinity (PA) of 245.3 kcal mol –1 and a gas basicity (GB) of 239 kcal mol –1 , are called superbases.…”

Section: Introductionmentioning

confidence: 99%

“…Depending on basic functional groups present in a molecule, neutral organic (super)bases may be grouped into several classes: amines, 1,4 amidines, 11 guanidines, 12 phosphazenes, 13 pyridines, 14 phosphines, 7b,15 and cyclopropenimines 16 (Scheme 1). A combination of these functionalities enables obtaining even more basic compounds, such as cyclopropeniminoguanidines, 17 guanidinophosphazenes, 18 and cyclopropeniminophosphazenes, 17b,19 also shown in Scheme 1.…”

Section: Introductionmentioning

confidence: 99%

“…The computational investigation of the basicity of superbases that contain substituents based on 1,2-( N , N -dimethylamino)-cyclopropenimine (in further text CPI) predicted that they should be more basic than guanidines 1,2,9 and possibly even phosphazenes. 13 In 2010 a convenient two-step synthesis of cyclopropenimines was reported by Alcarazo and co-workers, 25 which encouraged further research and development of superbasic compounds with a cyclopropenimine motif.…”

Section: Introductionmentioning

confidence: 99%

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Utilizing the Azaazulene Scaffolds in the Design of New Organic Superbases

Barić

2019

ACS Omega

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New neutral organic superbases with 1-azaazulene(s) as a molecular backbone are computationally designed, employing two basic substituents: dimethylaminocyclopropen-imines (CPI) and dimethylaminocyclopropeniminophosphazenes (CPI-P). Their proton affinities, gas basicities, and pKa values in acetonitrile are obtained using density functional theory. Azaazulenes substituted with CPI have a computed PA in the gas phase ranging between 272.9 and 306.8 kcal mol–1, with pKa values in acetonitrile between 28.8 and 36 units. The substitution with the CPI-P group resulted in even stronger superbases, with a PA from 296.5 to 335.2 kcal mol–1 and corresponding pKa values from 33.9 to 50 units. This exceptionally strong thermodynamic basicity is accompanied by very high kinetic basicity as well; contrary to typical proton sponges, the release of a proton from the conjugate superbase does not demand high activation energy. Because synthetic routes for both substituents and azaazulenes are already known, newly designed superbases represent suitable targets for synthesis and application.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Utilizing the Azaazulene Scaffolds in the Design of New Organic Superbases

Barić

2019

ACS Omega

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“…4 Advances in the field of design and synthesis of organic bases have been summarized lately in two review articles. 5,6 One particular molecular motif that leads to a highly basic organic compounds is susbtitution of guanidines and/or amines with substituents capable of forming intramolecular hydrogen bonds. Using this molecular motif Bachrach studied several very basic amines, with adamantane compound (II, Scheme 1) being the most basic one.…”

Section: Introductionmentioning

confidence: 99%

Towards the Strongest Neutral Organic Superbases Based on Intramolecular H-bonds

Barić¹,

Kovačević²

2014

Croat. Chem. Acta

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Abstract. Utilizing several different trialkylarsine oxides and substituted pyridine N-oxides as a hydrogen bond acceptors in tri-substituted guanidines we designed several very basic superbases possessing intramolecular hydrogen bonds (IHB-superbases), with proton affinity in the gas phase that comes very close to that of paradigmatic P4-tBu Schwesinger superbase and with pKa in acetonitrile up to 36 units.

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Cyclopropenimine as pincer ligand and strong electron donor in proton sponges

Barić

Kovačević

2016

J of Physical Organic Chem

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The basicity of cyclopropenimines (CPIs) and cyclopropenimino-based proton sponges is investigated by means of density functional theory (DFT) calculations and for the first time directly compared with the basicity of phosphazenes. It is found that CPIs are more basic than the corresponding phosphazenes in the gas phase. Proton sponges based on CPI as pincer ligands also possess higher or at least the same gas-phase proton affinity as proton sponges based on phosphazenes. However, in comparison with phosphazenes, CPI-based pincer ligands possess greater conformational flexibility, which enables almost complete avoidance of nitrogen lone pairs. This leads to the substantially smaller destabilization of neutral base in CPI proton sponges. Utilizing homodesmotic reactions, we have shown that significant contribution to the proton affinity of CPI proton sponges is an electron-donating effect of the second CPI substituent, whereas only a smaller portion of the stabilization energy should be attributed to intramolecular hydrogen bond. Further, it was shown that tetrasubstituted CPI naphthalenes possess very low ionization potential, which qualifies them as very strong electron donors. Finally, utilizing cyclopropenimino substituents, it was found that theoretical gas basicity limit of 370 kcal mol À1 recently calculated by Leito and coworkers could be extended beyond 370 kcal mol À1 in a case of cyclopropenimino phosphorus carbenes and cylopropenimino phosphorus ylides. Figure 3. Ball and stick representation of conformers (top view) of proton sponges 22-24 together with phosphazene sponge HMPN Scheme 4. Homodesmotic reactions referring to molecules 25-27 Scheme 3. Homodesmotic reactions referring to proton sponges 22-24

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Perspectives

Cited by 3 publications

References 20 publications

Utilizing the Azaazulene Scaffolds in the Design of New Organic Superbases

Utilizing the Azaazulene Scaffolds in the Design of New Organic Superbases

Towards the Strongest Neutral Organic Superbases Based on Intramolecular H-bonds

Cyclopropenimine as pincer ligand and strong electron donor in proton sponges

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