Isomeric Tetrakis(dimethylamino)naphthalenes: Syntheses, Structure-Dependence of Basicities, Crystal Structures, and Physical Properties

Abstract

For comparison to the recently described 2,3,6,7‐tetrakis(dimethylamino)naphthalene (1) the three isomers 2,3, and 4 were synthesized. The basicities of this group of isomers are strongly dependent upon the different mutual orientations of the pairs of dimethylamino substituents: only the isomers 3 and, partially, 4, both with dimethylamino groups in adjacent peri‐positions of the naphthalene, are strong “proton sponges”. For the isomers 1 and 2 with the same number and kind of twofold dimethylamino substituents in neighbouring ortho‐positions, however, no significant basicity increase is observed. To explain this difference between the two groups of isomers it is suggested that in the ortho‐pairs of 1 and 2 the C‐N bonds diverge considerably, leading to an increased N···N distance and consequently to less stable [N···H···N]+ hydrogen bonds in contrast to the parallel C‐N bonds in the peri‐substituted isomers 3 and 4. X‐ray crystal structure analyses of the bases and of some of the salts derived therefrom were solved and are discussed. Cyclic voltammetry indicates that 1 to 4 are strong electron donors, reacting easily to radical cations or dications which with suitable acids have been obtained as salts.

Theoretical studies on the proton affinities of four different series of nano-size diamines and designing strong superbases based on fullerene(C60) molecule

“…1a), is known as ''proton sponge" because of its high thermodynamic basicity combined with a kinetic inactivity to deprotonation that resembles the affinity of a sponge for water [14]. Since the discovery of DMAN as a superbase [13], many proton sponges have been created and they are finding a growing number of interesting applications [15][16][17][18][19][20][21]. One of the strongest superbases designed so far is TMGN (1,8-bis(tetramethylguanidino)naphthalene) shown in Fig.…”

Synthesis of 2-Alkynyl-, 4-Alkynyl-, and 2,7-Dialkynyl-1,8-bis(dimethyl­amino)naphthalenes and the Unexpected Influence of ortho-Alkynyl Groups on Their Basicity

“…8,15 The data obtained are presented in Table 1. As expected, 4-ethynyl derivatives 8a,b,d are 1-1.5 pK a units less basic than 1.…”

Heterocyclic superbases: retrospective and current trends

“…Thus, the basicity of compound 17f is 0.5 pK a unit lower than that for the parent compound 11. [28,30] 17e N --11.3 [28] 17f SiMe 3 2.92 -7.0 [31] At the same time, in the case of electron-donor ortho substituents, an increase in basicity accompanying the decrease in the N···N distance is always found. Here, we apparently have not only +I and +M effects of the ortho substituents but also a purely electrostatic factor related to the repulsion of the four adjacent lone electron pairs.…”