Macrocycles Bearing Ferrocenyl Pendants and their Electrochemical Properties upon Binding to Divalent Transition Metal Cations

Abstract

Metal complexes of Cu2+, Co2+, Cd2+, Zn2+, and Ni2+ formed with the ligands [Fc(cyclen)] (1) and [Fc(cyclen)2] (2) (Fc=ferrocene, cyclen=1,4,7,10‐tetraazacyclododecane) are synthesised and characterised. The X‐ray structure of the Cu2+ complex of 2, Fc([Cu(cyclen)(CH3CN)]2(ClO4)4, is reported, and shows that the two positively charged Cu2+‐cyclen units have a coordination number of five, adopting a distorted trigonal‐bipyramidal configuration. The Cu2+‐cyclen units are arranged in a trans‐like configuration with respect to the Fc group, presumably to minimise electrostatic repulsion. The voltammetric oxidation of the free ligands 1 and 2 in a CH2Cl2/CH3CN (1:4) solvent mixture yields two closely spaced oxidation processes. Both electron‐transfer steps are associated with the ferrocenyl moiety, implying strong communication between the cyclen nitrogen atoms and the ferrocenyl group. In contrast, cyclic voltammograms display only a simple reversible one‐electron process if 1 and 2 are complexed with Cd2+, Cu2+, Zn2+, Ni2+, or Co2+. Binding of these metal ions produces a significant shift in the reversible midpoint potential (Em). Except for Ni2+, Em is linearly proportional to the charge density of the transition metal ion, demonstrating that 1 and 2 may undergo redox switching. The diffusion coefficients of Fc, DmFc, 1 and 2, and their metal ion complexes correlate well with their molecular weights.

Ferrocene-Based Electrochemical Sensors for Cations

“…The interaction between Fc and amines has been the subject of extensive research due to its potential wide application range, including the design of metal ion receptors and sensors [8][9][10]63,[68][69][70][71][72]. However, despite numerous studies, the details of this interaction and the oxidation mechanism of ferrocene-bearing amine compounds have remained elusive until recently, where the oxidation mechanism of N,N-dimethylaminomethylferrocene (20, Fc-CH 2 -N(CH 3 ) 2 ), which can be considered as the parent ligand for many Fc receptors presented in this review, was evaluated and the oxidation product identified (Scheme 2) [7].…”

Formation of alkyne-bridged ferrocenophanes using ring-closing alkyne metathesis on 1,1’-diacetylenic ferrocenes

“…In some cases, a metal–iron interaction, e.g., as shown in complex IV [79], could be observed depending on the ring size of the ferrocenophane ligand [82–85]. Furthermore, ferrocenophanes functionalized with bridges containing various heteroatoms were utilized as ion sensors for a wide variety of applications [86–90]. An example (complex V ) with an additional diyne moiety is given in Fig.…”

Formation of alkyne-bridged ferrocenophanes using ring-closing alkyne metathesis on 1,1’-diacetylenic ferrocenes

“…[82][83][84][85] Furthermore, ferrocenophanes functionalized with bridges containing various heteroatoms were utilized as ion sensors for a wide variety of applications. [86][87][88][89][90] An example (complex V) with an additional diyne moiety is given in Figure 2 To the best of our best knowledge, no ferrocenophanes formed via RCAM have been reported to date. With this contribution, we would like to present the first RCAM of 1,1'-diacetylenic ferrocenes 1 (a: n =2; b: n = 3) to form the corresponding alkynebridged ferrocenophanes 2 (a: n =2; b: n = 3; Figure 2).…”