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.

Urea azines are a largely neglected class of compounds. We show herein that they can easily be synthesized and sublimed at higher temperatures (90–100 °C) without decomposition. Our discussion includes the derivatives N,N′‐diisopropylurea azine (2), tetramethylurea azine (3), and N,N′‐dimethylethyleneurea azine (4) as examples. Vibrational spectroscopy and quantum chemical calculations were used to study their electronic structure in detail. A clear trend in the calculated decomposition to N2 and carbene is found, but the analysis reveals that this trend reflects the stability of the carbene decomposition product rather than changes in the electronic structure of the urea azines. Using cyclic voltammetry (CV) measurements we show that the urea azines are strong organic electron donors, which can be oxidized reversibly in two well‐separated one‐electron steps. The radical salt 4(TCNQ), featuring radical monocations and radical monoanions, which form mixed stacks in the solid state, was prepared by reaction of neutral 4 with tetracyanoquinodimethane (TCNQ). Oxidation of 4 with silver salts Ag+X– (X = BF4 or PF6) was accompanied by dehydrogenation, leading to intensively red‐brown colored radical azoimidazolium dyes. Furthermore, urea azines were used as chelating ligands. In the case of 2, coordination to late transition metals initiates tautomerization. Reaction of 2 with boron hydrides leads to hydrogen elimination and formation of new B,N bi‐heterocyclic ring structures.

The reaction between BF(3)⋅OEt(2) and one of two guanidines, 1,8-bis(tetramethylguanidinyl)naphthalene (btmgn) and 1,2,4,5-tetrakis(tetramethylguanidinyl)naphthalene (ttmgn), yields the salts [(btmgn)(BF(2))]BF(4) and [(ttmgn)(BF(2))(2)](BF(4))(2). NMR spectroscopic data show that the boron atoms in the cation and anion exchange in the case of [(ttmgn)(BF(2))(2)](BF(4))(2), but not in the case of [(btmgn)(BF(2))]BF(4). The rate constant for this exchange was estimated to be 4 s(-1) at 80 °C for solutions in CH(3)CN. These salts were subsequently used for the reduction of dihalides Br(2) or I(2) to give polyhalide salts. We report the synthesis and first complete characterization (including structural analysis) of salts that contain pentabromide monoanions. In these salts, the Br(5)(-) anions interact to give dimeric units or polymeric chains. Our results are compared to previous quantum chemical calculations on the gas-phase structure of the Br(5)(-) anion. The possible pathways that lead to the polyhalides are evaluated. In the case of [(ttmgn)(BF(2))(2)](BF(4))(2), reduction is accompanied by ttmgn oxidation, whereas in the case of [(btmgn)(BF(2))]BF(4) reduction is initiated by aromatic substitution.

Hydrogen-atom transfer (HAT) is of key importance for several catalytic and biological processes, and provides an elegant access to C-H activation. In synthetic chemistry, a photoactivated metal complex is often employed to abstract an oxygen- or nitrogen-bound hydrogen, and the as-generated oxygen- or nitrogen-centered radical is the hydrogen-atom acceptor for HAT. Here, we report the first examples for HAT processes initiated by one-electron oxidation of urea azines. A further novelty is that the HAT-initiating oxidation can be realized by intramolecular ligand-metal electron transfer in copper(II)-urea azine complexes. These complexes are first characterized in the solid state, in which they are stable. Electron-transfer-initiated HAT processes are observed upon dissolving the complexes in organic solvents, and the kinetics of these processes varies with the solvent polarity. The carbon-centered radicals formed by HAT can either be trapped with 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) or undergo radical recombination reactions with itself, yielding diamagnetic end-products.

Reaction of the organic electron donors ttmgb [1,2,4,5‐tetrakis(tetramethylguanidinyl)benzene] and tdmegb [1,2,4,5‐tetrakis(N,N′‐dimethylethyleneguanidinyl)benzene] with two equivalents of silver dicyanamide, Ag(dca), yielded the two salts (ttmgb)(dca)2 (1a) and (tdmegb)(dca)2 (1b). Their relatively high N/C ratios motivated an analysis of their suitability as precursors to C,N materials. The compounds melt at around 200 °C and decompose at 220 (1a) and 245 °C (1b). Reactions of the organic electron donors with an excess of Ag(dca) resulted in coupled redox and coordination reactions, leading finally to coordination polymers with different dimensionalities. The oxidized guanidine units in the polymers are connected through Ag–dca–Ag bridges, leading to stacks of co‐planar C6 rings. The resulting cationic networks are neutralized by dca anions or anionic Ag(dca) chains.