A Tricopper(I) Complex Competent for O Atom Transfer, C–H Bond Activation, and Multiple O₂ Activation Steps

Abstract

Oxygenation of a tricopper(I) cyclophanate (1) affords reactive transients competent for C-H bond activation and O atom transfer to various substrates (including toluene, dihydroanthracene, and ethylmethylsulfide) based on H NMR, gas chromatography/mass spectrometry (MS), and electrospray ionization (ESI)/MS data. Low product yields (<1%) are determined for C-H activation substrates (e.g, toluene, ethylbenzene), which we attribute to competitive ligand oxidation. The combined stopped-flow UV/visible, electron paramagnetic resonance, ESI/MS, H NMR, and density functional theory (DFT) results for reaction of 1 with O are consistent with transient peroxo- and di(oxo)-bridged intermediates. DFT calculations elucidate a concerted proton-coupled electron transfer from toluene to the di(μ-oxo) intermediate and subsequent radical rebound as the C-H activation mechanism. Our results support a multicopper oxidase-like mechanism for O activation by 1, traversing species similar to the coplanar CuO unit in the peroxy and native intermediates.

Encapsulation of tricopper cluster in a synthetic cryptand enables facile redox processes from CuICuICuI to CuIICuIICuII states

“…Synthetic tricopper clusters have been a prominent synthetic target for the (bio)inorganic community over the past few decades, 1–9 since tricopper centers were identified/proposed as essential active sites for biological reduction of O 2 to H 2 O in multicopper oxidase (MCO) 10,11 and aerobic hydroxylation of methane in particulate methane monooxygenase (pMMO). 12 Although a tricopper active site in pMMO has been disputed, the conversion of methane to methanol was demonstrated with small-molecule tricopper complexes.…”

Cyclophanes as Platforms for Reactive Multimetallic Complexes

“…For example, reaction of Cu 3 (N 2 ) L Et/Me with N 2 O or other O atom sources (e.g., PhIO, Me 3 NO) affords the μ 3 -oxidotricopper complex, Cu 3 OL Et/Me (Figure 3). 61 Similarly, reaction with S 8 or Se metal yields the structurally related Cu 3 EL Et/Me (E = μ 3 -S, μ 3 -Se) compounds (Figure 3). 54,62 In contrast to reported Cu x E y complexes (x ≤ 3, y ≤ 2), the Cu 3 EL Et/Me (E = O, S, Se) series is atypical as E−E bonding interactions are not present and the bond metrics within the cyclophanate series are comparable.…”

“…For example, reaction of Cu 3 (N 2 ) L Et/Me with N 2 O or other O atom sources (e.g., PhIO, Me 3 NO) affords the μ 3 -oxidotricopper complex, Cu 3 O L Et/Me (Figure ). Similarly, reaction with S 8 or Se metal yields the structurally related Cu 3 E L Et/Me (E = μ 3 -S, μ 3 -Se) compounds (Figure ). , …”

Reversible O–O Bond Scission and O2 evolution at MOF-supported Tetramanganese Clusters

“…5,6 Attempts to mimic the natural systems with synthetic analogs have led to a number of elegant molecular clusters that shed light on the electron transfer events and stepwise mechanism of O-O bond cleavage and formation. [7][8][9][10][11][12][13][14][15][16][17][18][19] To our knowledge, however, the interconversion between molecular O2 and metal-oxo species in either synthetic or enzymatic discrete systems has not been documented. Here, we report that a tetramangenese cluster formed by self-assembly within a metal-organic framework (MOF) spontaneously cleaves the oxygen-oxygen double bond and reduces O2 by four electrons at room temperature.…”

“…Synthesizing molecular mimics capable of four-electron redox chemistry, which also provide multiple inward-oriented open metal sites for oxygen binding, as would be required for O-O coupling reactivity, has been difficult. 13,14,21,22 Furthermore, molecular mimics operating in solution are challenged by deleterious H-atom abstraction reactions that compete with bimolecular coupling of terminal or bridging oxo species that would give rise to O2. We sought to circumvent these issues by exploiting the site-isolation and potential for multi-electron chemistry of MOFs with multi-nuclear secondary-building units (SBUs).…”