A High‐Valent Heterobimetallic [Cu^III(μ‐O)₂Ni^III]²⁺ Core with Nucleophilic Oxo Groups

Abstract

A heterobimetallic CuNi bis(μ-oxo) diamond core is shown to possess nucleophilic oxo groups, and has been demonstrated for the first time as a viable intermediate during the deformylation of fatty aldehydes by cyanobacterial aldehyde decarbonylase.

Tuning the Reactivity of Terminal Nickel(III)–Oxygen Adducts for C–H Bond Activation

“…Therefore, we performed Ni K-edge X-ray absorption spectroscopy (XAS) on frozen solutions of both complexes. The Ni K-edge energy obtained for both 2b and 3b (8345 eV, Table 1) was within the range expected for Ni III ions, 19 and was almost the exact same as that obtained for 1b (8345 eV). 7 A comparison of the Ni K-edge X-ray absorption near-edge spectra (XANES)(Figures 4 and S44) showed little difference between precursor complexes 1–3a , suggesting that the anionic oxy-donor ligand does not dramatically affect the Ni K-edge energy (Figures 4, S45–S46, Table 1).…”

“…Analogous observations that identify no edge energy changes when comparing Ni II/III species, within comparable coordination environments, have previously been observed. 19a, 20 In this instance, contributions to the edge from 1 s -to-4 p absorption features distort the edge shape (~8340 eV), making determination of nickel oxidation state from edge energy alone challenging. We further note that the weak 1 s -to-3 d pre-edge transitions show modest 0.5–1 eV blue shifts (Table 1, Figure S46) upon conversion of 2a to 2b (8333.1 eV to 8333.6 eV) and 3a to 3b (8332.7 eV to 8333.8 eV), providing further evidence for an altered ligand field in 2–3b consistent with an increase in Ni oxidation state.…”

Mechanism of phenol oxidation by heterodinuclear Ni Cu bis(μ-oxo) complexes involving nucleophilic oxo groups

“…Complex 2 possesses a half-life of 9000 seconds at -50 °C, an order of magnitude higher than 1 (t 1/2 = 900 s at -50 °C). 17 However, the accumulated spectroscopic (absorption, X-ray absorption near-edge, resonance Raman, and electron paramagnetic resonance) properties (Figures S5-S6) of 2 are almost indistinguishable from those of 1 , indicating that 2 also possesses a heterodinuclear Cu III (μ-O) 2 Ni III core similar to 1 (Scheme 2). Thus, unlike homodinuclear dicopper-dioxygen chemistry, 25 where MeAN stabilized a μ-peroxo core, and AN stabilized a bis (μ-oxo) core, both of the MeAN and AN ligands lead to formation of a heterodinuclear Cu-Ni bis (μ-oxo) complex.…”

“…17 Treatment of a preformed solution of 1 with excess 2,4-di- tert -butylphenol led to pseudo-first order decay of the characteristic absorption feature of 1 at 895 nm (Figure 1A). The rate constant increases proportionally with the substrate concentration (Figure 1B), affording a second-order rate constant, k 2 , of 2.55 M −1 s −1 at -90 °C.…”

“…Unlike typical homodinuclear bis(μ-oxo) complexes, this species contains nucleophilic oxo groups that can carry out deformylation of aldehydes. 17 We initiated the present study to investigate whether the PCET mechanism established for phenol oxidation by homodinuclear Cu 2 O 2 cores having electrophilic oxo groups also persists for the Cu(μ-O) 2 Ni core of 1 , which has nucleophilic oxo groups. We report a systematic study of the oxidation of neutral phenols by 1 and provide deeper insights in the O-H bond activation mechanism towards substituted phenols by applying the Brønsted/Tafel analogy published by Ram and Hupp 18 for electron transfer processes.…”