Synthesis, Properties and Reactivity Studies of a Hetero‐dicopper Complex Consisting of a Porphyrin and a Bispyridylamine Moiety Connected by a Xanthene Backbone

Abstract

Synthesis, characterization and reactivity studies of a hetero‐dicopper complex, particularly towards oxygen reduction are presented. A bischlorido copper(II) trishistidine‐type coordination unit is positioned directly above a copper porphyrin unit. The close distance between the two coordination fragments is secured by a rigid xanthene backbone. Surprisingly, the dinuclear complex is not active towards oxygen reduction unlike the earlier published mononuclear analogues with a bispyridylamine copper center. However, the compound architecture of this multinuclear metal complex is interesting and can play an important role in the development of new catalysts for ORR.

Scaling Relation between the Reduction Potential of Copper Catalysts and the Turnover Frequency for the Oxygen and Hydrogen Peroxide Reduction Reactions

“…These correlations are in perfect agreement with a potential-determining reduction of Cu II to Cu I , followed by rate-limiting binding of O 2 for the entire series of copper species investigated here. In the case of Cu-tmpa, these potential- and rate-determining steps were already identified on basis of kinetic studies discussed in previous reports. ,, It is important to note that also the data previously obtained for Cu-bmpa ( E 1/2 = 0.30 V vs RHE, TOF max for ORR = 2.4 × 10 4 s –1 ) correlates very well with the ORR TOF max versus E 1/2 trend reported here, while catalysts that show very sluggish and therefore rate-determining Cu­(II) reduction kinetics do significantly underperform as one would expect. ,,, …”

“…22,23,62 It is important to note that also the data previously obtained for Cu-bmpa (E 1/2 = 0.30 V vs RHE, TOF max for ORR = 2.4 × 10 4 s −1 ) correlates very well with the ORR TOF max versus E 1/2 trend reported here, 39 while catalysts that show very sluggish and therefore rate-determining Cu(II) reduction kinetics do significantly underperform as one would expect. 39,47,63,64 Displacement of water for peroxide presumably takes place prior to the rate-determining step of the HPRR, and with similar energetics for all copper complexes, unlike the binding of dioxygen. The relative insensitivity of H 2 O 2 versus H 2 O binding to these copper sites is to be expected, as both species bind to the copper site in a very similar manner.…”

Proton Activation in the Presence of a Weak Acid Facilitated by Second Coordination Sphere Effects in Iron Porphyrins**

“…The Py 2 XPFe and TMPFe complexes display two one‐electron reductions within the investigated window, namely the Fe II/I and Fe I/0 reductions while the Fe III/II reduction is observed at more anodic potentials (Figure S4). The CuPy 2 XPFe complex also displays two, one‐electron reductions (the Fe II/I and Fe I/0 ), succeeding two earlier observable one‐electron reductions, with the first wave corresponding to the overlapping Fe III/II and Cu II/I couple (as one distorted wave) followed by the Cu I/0 couple [14,15] (Figure S5).…”

Directing the Selectivity of Oxygen Reduction to Water by Confining a Cu Catalyst in a Metal Organic Framework

“…Incorporating a catalyst by SALI allows it to retain its structure and its dynamics, while dimerization reactions and detachment from the electrode are prevented. [41][42][43][44][45] Given that the catalyst flexibility is of great importance for rapid ORR catalysis at single site copper species, [46,47] the SALI method is deemed as the most optimal. So far, catalysts that have been incorporated into MOFs by SALI include a nickel catalyst for ethylene dimerization, [48] an iridium catalyst for ethylene hydrogenation, [49] an iron porphyrin for photochemical CO 2 reduction [50] and molybdenum sulfide for electrocatalytic hydrogen evolution.…”