Oxygen Activation by a Copper Complex with Sulfur-Only Coordination Relevant to the Formylglycine Generating Enzyme

Abstract

Synthesizing hydrosulfido Cu thiolate complexes is quite challenging. In this report, two new and rare hydrosulfido Cu thiolate complexes, [Et4N]2[(mnt)­Cu-SH] (2, mnt = maleonitrile dithiolene = S2C2(CN)2) and [Et4N]3[(mnt)­Cu-(μ-SH)-Cu­(mnt)] (3), have been synthesized. Coordination sites and O2 activation by complex 2 resemble the formylglycine generating enzyme (FGE), an enzyme recently crystallographically characterized with sulfur-only coordination around Cu (three thiolate ligands). The function of this enzyme (and complex 2) is surprising because vulnerable thiolates should not be well suited for O2 activation rationally. Indeed, activation of oxygen by such an all-sulfur-coordinated Cu complex 2 is lacking in the literature. Aerial O2 (ambient O2 from the air) activation by complex 2 could proceed through a superoxide radical intermediate and a sulfur radical intermediate detected by resonance Raman (rR) spectroscopy and electron paramagnetic resonance (EPR) spectroscopy, respectively. The chemistry of 2 has been examined by its reactivity, crystal structure, and spectroscopic and cyclic voltammetric analyses. In addition, the results have been complemented with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations.

Evidence of Sulfur Non‐Innocence in [CoII(dithiacyclam)]2+‐Mediated Catalytic Oxygen Reduction Reactions

“…Based on detailed spectroscopic and theoretical studies the unique reactivities of the metal‐sulfur sites in oxidases and oxygenases has been attributed to the stabilization of reactive intermediates formed by the unfavorable one‐electron reduction of O 2 , by delocalization of the redox active orbitals onto the thioether or cysteinate sulfur atoms [4, 13] . Consistent with this explanation the presence of sulfur ligation is shown to induce novel dioxygen reactivity in bioinspired iron, [13, 17–20] copper, [21–23] manganese [24–26] and cobalt [26] complexes, which led to the stabilization of well‐defined metal‐oxygen intermediates. However, there is little evidence to support the redox non‐innocence of sulfur in these research works.…”

Redox Chemistry of “Neglected Copper‐Tris” Complex in Presence of Ascorbic Acid and O2

“…The empirical factor (g ∥ /A ∥ ) was 127 cm −1 suggesting that square planar structures fall in the range of 105–135 cm −1 . According to the Peisach–Blumberg diagram, [41] these parameter values predicted a complex of Cu II coordinated by mixed donor N and O atoms in distorted tetragonal or square‐pyramidal geometry [42–45] …”

“…According to the Peisach-Blumberg diagram, [41] these parameter values predicted a complex of Cu II coordinated by mixed donor N and O atoms in distorted tetragonal or squarepyramidal geometry. [42][43][44][45] The EPR spectrum of YGM1 also showed a rhombic signal with g 1,2,3 = 2.222, 2.087, 2.081 and A k =190×10 À 4 cm À 1 (g k /A k = 117 cm À 1 ) which were slightly different from the EPR parameters values of YGM2 suggesting different ligand environment and/or geometry at Cu II -centers (Figure 6b). The intensity ratio of YGM1 was 4 th times more than YGM2 suggesting that initially YGM1 was a prominent species but with time YGM2 was a prominent species.…”

Beweis von Schwefel‐non‐Innocence in [CoII(Dithiacyclam)]2+‐vermittelten, katalytischen Sauerstoff‐Reduktions‐Reaktionen

“…Umfangreiche spektroskopische und theoretische Studien deuten darauf hin, dass die einzigartige Reaktivität von Metall-Schwefel-Zentren in Oxidasen und Oxygenasen auf der Stabilisierung reaktiver Intermediate, die sich im Zuge der wenig bevorzugten Ein-Elektronen-Reduktion von Sauerstoff bilden, beruht, indem eine Delokalisierung der redoxaktiven Orbitale über die Schwefelatome der Thioether und der Cysteinate erfolgt. [4,13] Übereinstimmend mit dieser Erklärung zeigt die Anwesenheit von Schwefel in biologisch inspirierten Eisen-, [13,[17][18][19][20] Kupfer-, [21][22][23] Mangan- [24][25][26] und Kobalt- [26] Komplexen neue vielversprechende Reaktivitäten bezüglich der Stabilisierung von Metall-Sauerstoff-Intermediaten. Allerdings gibt es in den bisher erwähnten Studien nur wenige Beweise für die Annahme der Redoxaktivität des Schwefels.…”