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

• Published in: European journal of organic chemistry Vol. 2000; no. 8; pp. 1617 - 1622
• Main Authors: Staab, Heinz A., Kirsch, Annette, Barth, Thomas, Krieger, Claus, Neugebauer, Franz A.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag GmbH 01.04.2000; WILEY‐VCH Verlag GmbH
• Subjects: Basicity; Cyclicvoltammetry; Hydrogen bonds; Tetrakis(dimethylamino)naphthalenes
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/(SICI)1099-0690(200004)2000:8<1617::AID-EJOC1617>3.0.CO;2-C

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.