The Proton Affinity of the Superbase 1,8-Bis(tetramethylguanidino)naphthalene (TMGN) and Some Related Compounds: A Theoretical Study

Kovačević, Borislav; Maksić, Zvonimir B.

doi:10.1002/1521-3765(20020402)8:7<1694::aid-chem1694>3.0.co;2-d

Cited by 124 publications

(78 citation statements)

References 55 publications

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“…The calculated PA(3b) of 241.4 kcal mol À1 is further increased by substituting -NMe 2 groups with more basic moieties, as in 3c and 3d, 13a whose proton affinities assume PA(3c) = 260.3 and PA(3d) = 272.6 kcal mol À1 , being in a fair agreement with the earlier computed values of 257.7 33 and 274.0 kcal mol À1 , 13b respectively. Replacing the C-H groups at 4-and 5-positions on the naphthalene ring with the nitrogen atoms leads to 4b-4d, which change their most favorable protonation site to the pyridine nitrogen.…”

supporting

confidence: 85%

Engineering exceptionally strong oxygen superbases with 1,8-diazanaphthalene di-N-oxides

Despotović

Vianello

2014

Chem. Commun.

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DFT calculations revealed that 1,8-diazanaphthalene di-N-oxides provide extraordinary oxygen superbases, whose gas-phase and acetonitrile basicities surpass those of classical naphthalene-based nitrogen proton sponges. Such high basicity is almost entirely a consequence of a large strain-induced destabilization in neutral forms, while only a small contribution is offered by the intramolecular [O-HÁ Á ÁO] À hydrogen bonding upon protonation.For more than four decades, the design and synthesis of neutral organic superbases have attracted much attention 1-3 because their unique characteristics allow deprotonation of a wide range of weak acids resulting in weakly coordinated and highly reactive anionic species. Although usually weaker than their inorganic counterparts, uncharged organobases have become broadly used standard reagents in organic synthesis. Their practical usefulness involving mild reaction conditions, very good stability at low temperatures, efficient solubility in most organic solvents, and excellent recycling possibilities makes them superior to their ionic alternatives, 2,4 having an expansive range of applications in base-mediated transformations, 2 carbon dioxide storage, 5,6 and polymerization. 7 In 1968, Alder's discovery of the exceedingly high basicity of 1,8-bis(dimethylamino)naphthalene 8 (DMAN 1, Fig. 1) spurred interest in the area of neutral organic superbases, in particular, promoting a quest to create compounds with the highest basicity. 1-3 Since then, numerous diverse new superbases containing amines, imines, guanidines, phosphazenes, quinoimines, or cyclopropenimines have been synthesized, mostly by Staab, 9 Alder, 10 Schwesinger, 11 Verkade, 12 and other groups, 13 and their properties broadly characterized by means of experimental and computational methods. The extensive investigations by Koppel, Leito and their co-workers 14 should be highlighted, since they include both experimental and theoretical results in designing, preparing and measuring basicities of a huge variety of organic bases and superbases.A general feature of a large number of organic superbases is the presence of two (or more) basic centers that are placed close to each other and oriented in such a way that the incoming proton forms a strong stabilizing intramolecular hydrogen bond (Fig. 1). The favorable influence of multiple hydrogen bonds on enhancing the basicity (and acidity) of simple organic amines and alcohols has recently been particularly emphasized by Bachrach 15 and Kass. 16 Basic centers are usually nitrogen moieties due to their strongly attractive interactions with protons, since nitrogen lone pair orbitals are energetically higher-lying compared to, for example, those of oxygen in ethers and ketones, 17 in line with reports that ketones 18 and aldehydes 19 are less basic than the corresponding imines. 20 Yet, herein we wish to demonstrate that the oxygen basicity of N-oxides surpasses that of the related nitrogen compounds and that molecules containing two neighboring N-oxide moieties are sev...

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supporting

confidence: 85%

Engineering exceptionally strong oxygen superbases with 1,8-diazanaphthalene di-N-oxides

Despotović

Vianello

2014

Chem. Commun.

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“…It is well known that the unusually high basicity of proton sponges is significantly influenced by the formation of intramolecular hydrogen bonds [13]. The tendency of diamines and diols to form IMHBs has been recognized for quite some time [14][15][16][17][18], but only recently, several papers of Raczynska et al [19][20][21][22][23], Koppel and coworkers [24] and theoretical investigations of Maksić and coworkers [25][26][27] have shown that the existence of flexible intramolecular hydrogen bonds plays a significant role in the tailoring of organic superbases. A representative example is provided by a guanidine bearing three 3-(N,N-dimethylamino)propyl groups, for which a gas-phase basicity comparable to those of phosphazenes has been predicted [28].…”

Section: Introductionmentioning

confidence: 86%

Gas-phase proton affinities of guanidines with heteroalkyl side chains

Glasovac

Štrukil

Eckert‐Maksić

et al. 2008

International Journal of Mass Spectrometry

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“…It has been found that the quality of obtained geometry is not crucial if PAs are estimated by single-point calculations at higher levels of theory, which is the approach generally used. For instance, ZPE(HF/6-31G*) þ MP2/6-31 þ G*//MP2/6-31 þ G*; [37] ZPE þ MP2/6-311þþG**//HF/6-311þþ G**; MP2(fc)/6-311 þ G**//RHF/6-31G*; [71] BP86/TZVP//BP86/TZVP þ ZPE; [107] B3LYP/6-311 þ G(3df,3pd); [108] B3LYP/6-31 þ G**//HF/6-31G**; [8] BP/DZVP [6] and B3PW91/6-311þþg(d,p)//B3PW91/6-31G* methods have been the most successful. For larger molecular systems, a somewhat less accurate but computationally more efficient model, the High level computations such as CBS-QB3, CPCM/MP2/6-311 þ G**//CPCM/HF/6-31 þ G* and CPCM/B3LYP/6-311 þ G**//B3LYP/6-31 þ G** gave gas phase basicity and absolute aqueous pK a values with chemical accuracy [110].…”

Section: Theoretical Methodsmentioning

confidence: 99%

“…This value is comparable with basicities of MTBD (7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene) and PMG in acetonitrile and it is by 5.2 pK a units higher than DMAN (1). In a subsequent paper, Kova cevi c and Maksi c report theoretical PA and pK a values for TMGN and related proton sponges (Table 2.8), as well as giving an insight into the origin of the high basicity of TMGN [71]. The basicity of these bisguanidines is the combined result of the unfavourable nonbonded repulsions in the initial base, the large PA of guanidine group and strong IMHB present in the protonated species.…”

Section: Guanidinesmentioning

confidence: 99%