Proton sponges dications

An interesting situation occurs in the dication of the doubly protonated proton sponge 35 2H+ and in the zwitterion of 4,5-dihydroxy-l,8-bis(dimethylamino)naphthalene (111). The asymmetry of both hydrogen bridges in these systems is clearly controlled by electrostatic factors in order to obtain maximal separation of the two positively charged centres in 35 2H+ and, in reverse, to gain an attraction between the cationic and anionic centres in 111. 

The oxidation of compound 32 occurs in a similar manner but even more easily136. Its radical cation can be stored unchanged in acetonitrile for months. The UV spectrum of 32+ (7.max = 480 nm, lg e = 3.1) is very close to that of neutral 32 itself, from which one can conclude that the naphthalene moiety does not take part in the oxidation. As found by cyclovoltammetry, the double proton sponge 35, unlike its isomer 79, is oxidized with reversible two-electron transition, composed of two superimposed one-electron steps at Eli2 —0.50 V (Table 13)45. Apparently, the driving force for this process is the formation of the resonance-stabilized dication 133 (equation 8), which was isolated in the form of black crystals with I3- anions (kmax = 643 nm, lg e = 4.02) and investigated in... 

Similarly, non-separable two-electron transitions were also observed for proton sponges 65, 66 and tetraamine 13454,58. As seen from Table 13, compound 35 is the strongest electron donor among all known tetrakis(dimethylamino)naphthalenes. The oxidation of 65 with four mole equivalents of iodine at low temperature also led to the formation of a black-brown salt (/.max = 723 nm, lg e = 4.31) of the dication 13558. 

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