1,2,4,5-Tetrakis(tetramethylguanidino)benzene: Synthesis and Properties of a New Molecular Electron Donor

The molecular electron donor 1,2,4,5-tetrakis(tetramethylguanidino) benzene (ttmgb) was synthesised by reaction between 1,2,4,5-tetraaminobenzene and 2-chloro-1,1',3,3'-tetramethylformamidinium chloride. Protonation and oxidation of the molecule were analysed. In the course of titration of initially yellow-coloured solutions of ttmgb with HCl intense and fully reversible colour changes were observed; the di- and tetraprotonated forms are green- and blue-coloured, respectively. The tetraprotonated molecule crystallised with Cl-, and the diprotonated molecule crystallised with PF6- as counterions. Oxidation, which already occurs slowly in air, was followed by CV measurements. Oxidation with I-2 leads to deeply green-coloured solutions, from which purple-black crystals of (ttmgb)(I-3)(2) of metallic appearance and a layer structure were obtained. The analysis of the molecular structure shows that the pi system has rearranged with loss of the aromatic benzene system. Quantum chemical calculations suggest ttmgb to be an excellent two-electron donor superior even to the "organic sodium" tetraazafulvalene in the gas phase. However, in polar solvents (modelled with the COSMO model) the situation changes (in line with the experimental results from CV measurements), as the dication of tetraazafulvalene is considerably more solvent stabilised than [ttmgb](2+). ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)