Syntheses and Properties of Cycloamidines Based on 4H-Imidazoles

Abstract

Employing three different syntheses a broad spectrum of 4H-imidazoles 3a - 3s has been synthesized. In the course of the two-fold aminolysis reaction leading to derivatives 3q - 3s, deeply colored byproducts could be isolated and structural characterized.These novel donor-acceptor derivatives of type 7 consist of an 1H- and 4H-imidazole which are connected by a nitrogen bridge and rearrange via rapid 1,3-/1,5-hydride shifts. Using 1H NMR experiments the aminolysis product 3p shows prototropic isomers which could be detected in equilibrium for the first time. Cyclovoltammetric measurements of a series of substituted 2-aryl derivatives 3d - 3i displayed two reversible single electron transfer steps with relatively small semiquinone formation constants between 102 and 4×103. The 4H-imidazole 3d was successfully converted into boratetraaza-pentalene 8a, which showed two well separated reduction potentials. The value of semiquinone formation constant of 8a (1.8×1015) is even higher than those reported for similar derivatives. 4H-imidazoles can also be employed for the efficient complexation of catalytically important metals as exemplified by copper complexes 11 and 12. Derivative 3m, which possesses an additional chelating pyridine substructure, formed a stable complex of structural composition Zn(3m)2 with diethyl zinc

Ligand‐Induced Donor State Destabilisation – A New Route to Panchromatically Absorbing Cu(I) Complexes

“…Four reduction waves are observed for complex 6, which are all ligand-based. This is in agreement with the two electron reductions, reported for the parent 4H-imidazoles [48][49][50] as well as for the [Cu(I)(xantphos)(4H-imidazolato)] complexes. [31,37] In the Zn(II) complex 6, both ligands are similarly strong coupled (based on the half-step potential difference), but the nominal + 2 charge of the zinc ion stabilizes four reduction steps in a comparable potential window with respect to the copper complexes.…”

“…All electrochemical reduction events are attributed to be ligandbased. This assignment is based on the comparison of the observed reduction potentials with those of the parent 4Himidazoles [48][49][50] as well as with the earlier reported [Cu-(I)(xantphos)(4H-imidazolato)] complexes. [31,37] All studied cuprates feature two reversible or quasi-reversible reduction waves (E I red , E II red ; see Table 1), followed by an irreversible reduction wave (E III red ).…”

Synthesis of Ligands Based on 4H‐Imidazoles and Pyridine Subunits: Selective Complexation and Bathochromically Absorbing Complexes

“…The filtrate was again evaporated to dryness and purified by column chromatography (alumina, activity V, toluene at the beginning, then toluene/ethanol, 1:1); yield 190 mg (54 %). Analytical data were in agreement with those reported 13c…”

“…Recently, we reported the synthesis of the pyridyl‐substituted 4 H ‐imidazole 1a (R = 2‐pyridyl, Ar = 4‐tolyl)13c starting from the commercially available pyridyl‐2‐carbamidine. Its synthesis has now been improved using cheaper 2‐cyanopyridine as the starting material.…”

Photophysics of Ru(II) Dyads Derived from Pyrenyl-Substitued Imidazo[4,5-f][1,10]phenanthroline Ligands

“…For imidazole-containing ligands, it has been shown that the protonation state of the imidazole ring significantly impacts the photophysical properties of both the isolated ligands [42][43][44] and their respective transition metal complexes [45][46][47] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60…”