Electrochemical behaviour of complexes of copper(II) with 14-membered saturated tetra-aza macrocycles

Abstract

The electrochemistry of copper(II) with three 14-membered saturated tetra-aza macrocyclic ligands (L) is reported. Both anodic and cathodic electrode processes involve complicated mechanisms; nevertheless cyclic voltammetry at high potential scan rates allowed evaluation of the E½ values for the couples [CuL]3+–[CuL]2+ and [CuL]2+–[CuL]+. Reduction and oxidation mechanisms have been studied and the half-life of the species [CuL]3+ anodically electrogenerated has been evaluated. The thermodynamic data are discussed

Electrocatalytic Reduction of CO2by Copper (II) Cyclam Derivatives

“…Despite the slightly different experimental conditions, it can be stated that the electrocatalytic CO 2 reduction by Cu(II)-cyclam takes place near the thermodynamic potential. During the anodic scan, however, a large oxidation peak (peak C or peak C') appears at around 0.0 V, which is attributed to the oxidation of Cu(I) ion/Cu atom released from Cu(I)-cyclam [12]. This manifests a severe demetalation behavior of Cu(II)-cyclam, which is a critical drawback as an electrocatalyst for CO 2 reduction.…”

“…The reduction of Cu(II)-cyclam takes place through two steps. A Cu(II)/ Cu(I) peak appears at -0.85 V (peak A), a Cu(I)/Cu(0) peak at -1.05 V (peak B) [12], and the solvent decomposition current follows at below -1.2 V. In a CO 2 -saturated solution, the reduction currents are notably increased and the peak potentials are shifted to positive direction (i.e., -0.81 V (peak A') and -0.97 V (peak B')). The onset potential of CO 2 reduction by Cu(II)-cyclam is determined about -0.7 V, which is much less negative than that by Ni(II)-cyclam (-1.18 V).…”

“…It has been known that Cu(I)-cyclam is unstable so that Cu(I) ion is liberated from the complex upon a cathodic polarization, which is a serious drawback as an electrocatalyst [12,13]. This demetalation issue, however, has not been fully addressed yet.…”

“…In contrast to the extensive works on Ni(II)-cyclam, the studies on the cyclam complexes of other transition metals (e.g., Co, Cu) are scarce [11][12][13][14][15]. It has been known that Cu(I)-cyclam is unstable so that Cu(I) ion is liberated from the complex upon a cathodic polarization, which is a serious drawback as an electrocatalyst [12,13].…”

“…This demetalation issue, however, has not been fully addressed yet. It was reported that the both the smaller and larger macrocyclic complexes than 14-membered cyclam leads to stabilization of Cu(I) state, and thus suppressed demetalation behavior [12,13]. It was also claimed that the N-alkylation of cyclam stabilizes the Cu(I)-and Ni(I)-cyclams both by increasing the cavity size and by decreasing the ligand field strength imparted by the nitrogen donor atom [15], which leads to a positive shift in the M(II)/M(I) potential [14,15].…”