Ferrocene–Cyclam: A Redox-Active Macrocycle for the Complexation of Transition Metal Ions and a Study on the Influence of the Relative Permittivity on the Coulombic Interaction between Metal Cations

Abstract

The reaction of 1,1'-ferrocene-bis(methylenepyridinium) salt with 1,4,8,11-tetraazacyclotetradecane-5,12-dione, followed by LiAlH4 reduction results in the formation of FcCyclam. Metal complexes of FcCyclam with M2+ = Co2+, Ni2+, Cu2+, and Zn2+ were synthesized from FcCyclam and the respective metal triflates. The complexation of Cu2+ and FcCyclam in CH3CN is preceeded by a rapid electron transfer, followed by a slower complex formation reaction and a reverse electron transfer. The protonation constants of FcCyclam and the stability constants for the Cu2+ complex of FcCyclam (logK = 9.26(4) for the formation of the [Cu(FcCyclam)]2+ complex) were determined in 1,4-dioxane/water 70:30 v/v, 0.1 moldm(-3), KNO3, 25 degrees C. By using FcCyclam one can selectively sense the presence of Cu2+ ions in the presence of Ni2+, Zn2+, Cd2+, Hg2+, and Pb2+ with a very large deltaE approximately 200 mV, depending on pH. The X-ray crystal structures of FcCyclam and of complexes with Co2+, Ni2+, Cu2+, and Zn2+ were determined and Fe-M2+ distances obtained: Fe-Co2+ 395.9, Fe-Ni2+ 385.4, Fe-Cu2+ 377.7, and Fe-Zn2+ 369.0 pm. The redox potential of FcCyclam is influenced in a characteristic manner by the complexation of M2+. A linear correlation of 1/r approximately/= deltaE [r = distance Fe-M2+ from crystal data, deltaE=-E1/2([M(FcCyclam)]2+) - E1/2(FcCyclam)] was found; this is indicative of a mainly Coulomb type interaction between the two metal centers. The nature of the Fe...M2+ interaction was also investigated by determining deltaE in several solvents (mixtures) of different dielectric constants epsilon. The expected relation of deltaE approximately/= 1/epsilon was only found at very high values of epsilon. At epsilon < 40 increased ion-pairing appears to reduce the effective positive charge at M2+ leading to progessively smaller values of deltaE with lowered epsilon. The dependence of deltaE and epsilon can be calculated semiquantitatively by combining the Fuoss ion-pairing theory with the Coulomb model.

Ferrocenoyl-amino acids: redox response towards di- and trivalent metal ions

“…In recent years, there has been an interest in the electrochemical detection of ion binding to a ligand which is equipped with a redox active group, such as ferrocene (Fc) or cobaltocene [1][2][3][4][5][6][7][8][9][10][11]. The specificity of the system is dictated by the ligand-ion interactions and detection sensitivity depends on the efficiency of the electronic communication between the ligand-ion complex and the redox group, either through-space or through-bond.…”

“…The specificity of the system is dictated by the ligand-ion interactions and detection sensitivity depends on the efficiency of the electronic communication between the ligand-ion complex and the redox group, either through-space or through-bond. Various Fc substituted macrocycles such as cyclams [2], cryptands [1,3], aza-crowns [4], crown ethers [12], and calixarenes [9] have been shown to electrochemically sense the coordination of alkaline-, alkaline earth-, transition-metals and lanthanide ions. Furthermore, peptides are known to show specificity towards metal binding, as was determined by titration experiments using NMR [5][6][7], potentiometry [11], luminescence measurements [8] FT-IR, CD and UV-vis spectroscopy [10].…”

Synthesis, characterization and X-ray crystal structures of cyclam derivatives. Part VI. Proton binding studies of a pyridine-strapped 5,12-dioxocyclam based macrobicycle

“…The design and synthesis of macropolycyclic receptors incorporating ligating heteroatoms are actively pursued for the development of functional nanodevices. [2][3][4][5] Selective molecular recognition 6,7 and signalling [8][9][10][11][12] properties are sought to provide the major impetus for further progress in this flourishing area of chemistry, while various applications in biochemistry and medicine, catalysis, or material sciences have already opened new horizons for the utilization of this class of compounds. [13][14][15][16][17] In this respect, conformationally constrained bicyclic polyamines with bridgehead nitrogen atoms have gained increasing attention over the last three decades because the additional rigidity provided by strapping the macrocyclic framework imparts intriguing anion- 18 and metal-binding properties.…”

“…35,36 In contrast, amide-containing azamacrobicyclic ligands have attracted much less attention, 37 although they provide a convenient access to strapped cyclen or cyclam derivatives upon reduction of the protecting carbonyl groups. 8,9,[38][39][40][41] From a synthetic point of view, trans-dioxocyclam (5,12-dioxocyclam or 1,4,8,11-tetraazacyclotetradecane-5,12-dione, compound 1 in Scheme 1) 42,43 is an attractive starting material since two out of the four secondary amines of the 14-membered ring, namely those located in positions 4 and 11, take part in two peptidic bonds and thus are masked. Optically active C-functionalized analogs, obtained by photolysis of chromium carbene complexes in the presence of suitable imidazolines, have been described more recently by Hegedus and coworkers.…”

Electrochemical sensing of anions by redox-active receptors built on the ferrocenyl cyclam framework

“…Moreover, the insertion of a transition metal ion into the macrocyclic cavity may lead to enhanced recognition properties. Previous studies have shown that ferrocenyl-substituted polyazamacrocycles are good candidates for the electrochemical recognition of anions [13,[18][19][20][21][22][23][24]. In this paper, we present a new series of ferrocenyl ionophores, L 1 , L 2 , L 3 and L 1 Cu, (Scheme 1) designed for anionic sensing.…”