New Iron(II) and Manganese(II) Complexes of Two Ultra-Rigid, Cross-Bridged Tetraazamacrocycles for Catalysis and Biomimicry

Abstract

The high-spin dichloro Mn 2+ and Fe 2+ complexes of 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (1) and 4, 10-dimethyl-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane (2) provide durable new compounds of these elements for important fundamental studies and applications. The compounds are especially noteable for their exceptional kinetic stabilities and redox activity. The X-ray crystal structures of all four complexes demonstrate that the ligands enforce a distorted octahedral geometry on the metals with two cis sites occupied by labile chloride ligands. Magnetic measurements reveal that all are high spin with typical magnetic moments. Cyclic voltammetry of the complexes shows reversible redox processes at +0.110 and +0.038 V (versus SHE) for the Fe 3+ /Fe 2+ couples of Fe(1)Cl 2 and Fe(2)Cl 2 , respectively, while the Mn 3+ /Mn 2+ and Mn 4+ /Mn 3+ couples were observed at +0.585 and +1.343 V, and +0.466 and +1.232 V for the complexes Mn(1)Cl 2 and Mn(2)Cl 2 , respectively. Mn 2+ (1) was found to react with H 2 O 2 and other oxidizing agents to produce the Mn 4+ (1) complex. The catalytic efficacy of Mn 4+ (1) in aqueous solution has been assessed in the epoxidation reaction of carbamazepine and hydrogen abstraction reaction with 1,4-cyclohexadiene. The complex has been found to be a selective catalyst, exhibiting moderate catalytic activity in oxygen transfer, but significantly more effective catalytic activity in hydrogen abstraction reactions.

Does a Reinforced Kinetic Macrocyclic Effect Exist? The Demetallation in Strong Acid of Copper(II) Complexes with Open and Cyclic Tetramines Containing a Piperazine Fragment

“…In particular, they are alternatively placed above and below the mean plane, thus giving rise to a slight tetrahedral distortion of the square-planar Cu II coordination. Such a distortion is not present in the previously discussed [Cu II (3)](ClO 4 ) 2 complex (in which the four N atoms deviate, on average, by 0.03(1) ä from the best plane displaced by 0.11(1) ä from the metal centre). Moreover, no distortion is observed in the corresponding complex of plain cyclam, [Cu II (1)] 2 + , [6] in which the metal centre is perfectly coplanar with the four secondary nitrogen atoms and the two perchlorate ions are symmetrically located along the z axis, at a distance of 2.57 ä.…”

“…[3] As an example, compound 2 is a laterally reinforced cyclam, in which two nitrogen atoms are linked by two ethylenic chains, thus giving rise to a piperazine ring. Such a ring typically displays a rich conformational activity, similar to that of cyclohexane.…”

Reactivity of Molecular Dioxygen towards a Series of Isostructural Dichloroiron(III) Complexes with Tripodal Tetraamine Ligands: General Access to μ‐Oxodiiron(III) Complexes and Effect of α‐Fluorination on the Reaction Kinetics

“…These values lie in the expected range for neutral electrolytes and thus indicate that dissociation must be minor at these concentrations: by comparison, L values close to 100 and 150 S cm 2 mol À1 were found for pure mono-and dicationic species, respectively. [24,31,34] All data are listed in Table 3. FeCl 2 is qualitatively identical to that already reported for the brominated analogue BrTPAFeCl 2 , and assignment can easily be made by direct comparison.…”

Discovery of Antischistosomal Drug Leads Based on Tetraazamacrocyclic Derivatives and Their Metal Complexes

“…Within the past decade, these macrocycles have become important structural moieties for a variety of diagnostic and therapeutic pharmaceutical agents (21). Our group has been actively involved in the synthesis of these macrocyclic polyamines and their metal complexes and demonstrated their activities against HIV through CXCR4 inhibition (22)(23)(24)(25)(26)(27). We have recently employed the metal coordination approach to prepare a series of metal complexes using cross-bridged and side-bridged tetraazamacrocyclic ligands and have shown that both the ligands and their metal complexes are effective antimalarial agents (22,28).…”

“…1) for their activities against S. mansoni in vitro and in vivo and present here our findings on their antischistosomal activity. Seven of these 26 compounds (compounds 8, 9, 15 to 17, 20, and 21) are newly described in this report, and for the other compounds, either their antiviral or antimalarial activities have been described previously or they have been submitted elsewhere for synthetic method development and/or to report their antiviral or antimalarial activities (21)(22)(23)(24)(25)(26)(27)(28)(29)(30).…”