Ascorbic Acid as an Aryl Radical Inducer in the Gold-Mediated Arylation of Indoles with Aryldiazonium Chlorides.

In recent years interest in the development of protocols that facilitate the oxidative addition of gold to access mild cross-coupling processes mediated by this metal has increased. In this context, we report herein that ascorbic acid, a natural and readily accessible antioxidant, can be used to accelerate the oxidative addition of aryldiazonium chlorides onto AuI . The aryl-AuIII species generated in this way, has been used to prepare 3-arylindoles in a one-pot protocol starting from anilines and para-, meta-, and ortho- substituted aryldiazonium chlorides. The mechanism underlying the oxidative addition has been examined in detail based on EPR analyses, cyclic voltammetry, and DFT calculations. Interestingly, we have found that in this protocol, the chloride atom induces the AuII /AuIII oxidation step.

Antileishmanial activity of quinazoline derivatives: synthesis, docking screens, molecular dynamic simulations and electrochemical studies.

A series of quinazoline-2,4,6-triamine were synthesized and evaluated in vitro against Leishmania mexicana. Among them, N(6)-(ferrocenmethyl)quinazolin-2,4,6-triamine (H2) showed activity on promastigotes and intracellular amastigotes, as well as low cytotoxicity in mammalian cells. Docking and electrochemical studies showed the importance of both the ferrocene and the heterocyclic nucleus to the observed activity. H2 is readily oxidized electrochemically, indicating that the mechanism of action probably involves redox reactions.

Solvent and pH effects on the redox behavior and catecholase activity of a dicopper complex with distant metal centers.

A dicopper complex is described for which significant catecholase activity was found, particularly for a compound in which the two metal ions are more than 7A apart. Variations on the catecholase activity of this complex were explored in a range of pH values from 5.5 to 9.0 in two solvent mixtures, MeCN/H(2)O and MeOH/H(2)O. The catalytic performance of the complex was found to be substantially better in the second, where the maximum activity was achieved at a pH value one unit lower than in the first. Electrochemical studies of the complex in the absence and presence of dioxygen revealed a very different behavior in each of the two solvent mixtures, which may account for the correspondingly distinct catalytic activity.

On the mechanism of iron(III)-dependent oxidative dehydrogenation of amines.

Kinetic and structural data are presented for the iron-promoted dehydrogenation of the amine, [Fe(III)L3]3+ (1), L3 = 1,9-bis(2'-pyridyl)-5-[(ethoxy-2''-pyridyl)methyl]-2,5,8-triazanonane. Spectroscopic and electrochemical experiments under the exclusion of dioxygen helped to identify reaction intermediates and the final product, the Fe(II)-monoimine complex [Fe(II)L4]2+ (2), L4 = 1,9-bis(2'-pyridyl)-5-[(ethoxy-2''-pyridyl)methyl]-2,5,8-triazanon-1-ene. 2 is formed by disproportionation of the starting complex 1 by a three-step reaction mechanism, most likely via ligand-centered radical intermediates. The rate law can be described by the second-order rate equation, -d[(Fe(III)L3)3+]/dt = k(EtO)- [(Fe(III)L3)3+][EtO-], with k(EtO)- = 4.92 +/- 0.01 x 104 M(-1) s(-1) (60 degrees C, mu = 0.01 M). The detection of general base catalysis and a primary kinetic isotope effect (k(EtO)-(H)/k(EtO)-(D) = 1.73) represents the first kinetic demonstration that the deprotonation becomes rate determining followed by electron transfer in the oxidative dehydrogenation mechanism. We also isolated the Fe(II)-monoimine complex 2 and determined its structure in solution (NMR) and in the solid state (X-ray).

A dicopper complex with distant metal centers. Structure, magnetic properties, electrochemistry and catecholase activity.

The crystal structure and magnetic properties of a dinuclear copper(II) complex of the ligand [2,8-dimethyl-5,11-di-(dimethylethyleneamine) 1,4,5,6,7,10,11,12-octahydroimidazo [4,5-h] imidazo [4,5-c] [1,6]diazecine] dimeim have been investigated. Also, its catecholase activity has been explored in different solvent mixtures: MeCN/H2O and OH/H2O, each at several pH values. In CH3OH/H2O, where the activity was superior, the optimal pH value for the catalytic activity was found to be lower than in CH3CN/H2O. The study of the complex's electrochemical behavior (cyclic voltammetry) which was also investigated in these various media, revealed that although an increase in pH in both solvent mixtures results in an increase both in Me oxidizing power (E(1/2)) and reversibility (ipa/ipc) the change of solvent system seems to be a more influencing factor. The superior catalytic activity found in MeOH/H2O pH=8.0, is associated with a significantly more reversible behavior displayed in this medium. Potentiometric determination of the overall formation constant and three successive pKas for the complex, suggest the formation of stable hydroxo complexes which could be the catalytically active species.