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.
In the context of our studies on relatives of l,s-bis(dimethy1amino)naphthalene 1 ("proton sponge"),". 21 the comparison with 1,4,5,8-tetrakis(dimethylamino)naphthalene 2 was of interest, which contains twice the pairwise peri-arrangement of dimethylamino groups associated with "proton sponge" properties. This posed the question of the mutual influence of these two structural units, which should be evident from the pK, values for the first and second protonation steps of 2. Moreover, being a structural isomer of the recently prepared 2,3,6,7-tetrakis(dimethylamino)naphthalene 3J3I 2 was of interest as an electron donor in which formally two structural units corresponding to the 1 ,Chis-(dimethy1amino)benzene ("tetramethyl-para-phenylenediamine," TMPD) are coupled together.
The dication salt 4·(I3–)2 of 1,4,5,8-tetrakis(dimethylamino)naphthalene 3 is isolated and its molecular structure established by X-ray crystallographic analysis; spectral data of 4 are compared with those of the dication 2 of 1,4-bis(dimethylamino)benzene, determined in the presence of an oxidant, i.e. Br2, Ag+
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