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-1,1Ј,3,3Ј-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 diand tetraprotonated forms are green-and blue-coloured, respectively. The tetraprotonated molecule crystallised with Cl -, and the diprotonated molecule crystallised with PF 6 -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
Organic electronics on demand? The palladium‐catalyzed coupling of aromatic ortho‐diamines with substituted dichloroquinoxalines furnishes N,N‐dihydrotetraazaacenes, which were oxidized by MnO2 into the corresponding tetraazapentacenes (see structures; N blue, Cl green, Si yellow). The modular synthesis of these acenes allows the introduction of any substituent by choice of the proper quinoxaline derivative.
In this work we report on the syntheses and properties of several new Ni complexes featuring the chelating bisguanidines bis(tetramethylguanidino)benzene (btmgb), bis(tetramethylguanidino)naphthalene (btmgn), and bis(tetramethylguanidino)biphenyl (btmgbp) as ligands. All complexes were structurally characterized by single-crystal X-ray diffraction and quantum chemical calculations. A detailed inspection of the magnetic susceptibility of [(btmgb)NiX(2)] and [(btmgbp)NiX(2)] (X=Cl, Br) revealed a linear temperature dependence of chi(-1)(T) above 50 K, which was in agreement with a Curie-Weiss-type behavior and a triplet ground state. Below approximately 25 K, however, magnetic susceptibility studies of the paramagnetic d(8) Ni complexes revealed the presence of a significant zero-field splitting (ZFS) that results from spin-orbit mixing of excited states into the triplet ground state. The electronic consequences that might arise from the mixing of states as well as from a possible non-innocent behavior of the ligand have been explored by an experimental charge density study of [(btmgb)NiCl(2)] at low temperatures (7 K). Here, the presence of ZFS was identified as one potential reason for the flat angle-spherical Cl-Ni-Cl deformation potential and the distinct differences between the angle-spherical X-Ni-X valence angles observed by experiment and predicted by DFT. An analysis of the topology of the experimentally and theoretically derived electron-density distributions of [(btmgb)NiCl(2)] confirmed the strong donor character of the bisguanidine ligand but clearly ruled out any significant non-innocent ligand (NIL) behavior. Hence, [(btmgb)NiCl(2)] provides an experimental reference system to study the mixing of certain excited states into the ground state unbiased from any competing NIL behavior.
New binuclear complexes of three-coordinate Cu I have been synthesized with the ligand 1,2,4,5-tetrakis(tetramethylguanidino)benzene (ttmgb). Subsequent oxidation of the ligand unit was achieved by reaction with Br 2 or I 2 . Reaction with Br 2 leads to oxidation of both the ligand and the copper ions and formation of a bicationic dinuclear Cu II complex. On the other hand, oxidation with I 2 leads only to oxidation of the ligand during the first step. A metastable coordination polymer of ladder-type structure results, in which the coordi-
Herein we report on the synthesis of the new strong N‐base and electron donor tdmegb [1,2,4,5‐tetrakis(N,N′‐dimethylethyleneguanidino)benzene]. Compared to the previously synthesized ttmgb [1,2,4,5‐tetrakis(tetramethylguanidino)benzene], this compound turned out to be a slightly better electron donor and a slightly weaker base. In experiments in which [AuCl(PPH3)] was dissolved in CH3CN together with tdmegb, we observed the formation of the first cyanomethyl complex of Au, namely [Au(CH2CN)(PPh3)] in good yield. This reaction does not take place for ttmgb. Moreover, in CH2Cl2 solutions containing the three components [AuCl(PPh3)], tdmegb and a nitrile (in large excess), only AuI reduction leading to a [Au11Cl3(PPh3)7] cluster is observed. Possible reaction mechanisms for this unusual reaction are discussed.
Substitution of the aromatic hydrogen atoms in the electron donors 1,2,4,5‐tetrakis(tetramethylguanidino)benzene (1a) and 1,2,4,5‐tetrakis(N,N′‐dimethyl‐N,N′‐ethyleneguanidino)benzene (1b) by iodide (to give 2a and 2b) and nitro groups (to give 3a and 3b) afforded new redox‐active ligands. Their properties (electron donor capacity, Brønsted basicity and optical spectra) have been analyzed and compared with the unsubstituted 1,2,4,5‐tetrakis(guanidino)benzenes. The experimental results are supplemented by quantum chemical calculations. The first late‐transition metal complex of the push–pull ligand 3a was prepared and characterized and its oxidation studied.
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