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

Abstract

Oxidation of phenols by heterodinuclear CuIII(μ-O)2NiIII complexes containing nucleophilic oxo groups occurs by both proton coupled electron transfer (PCET) and hydrogen atom transfer (HAT) mechanisms; the exact mechanism depends on the nature of the phenol as well as the substitution pattern of the ligand bound to Cu.

Critical Aspects of Heme–Peroxo–Cu Complex Structure and Nature of Proton Source Dictate Metal–Operoxo Breakage versus Reductive O–O Cleavage Chemistry

“…While smaller than expected for a phenolic HAT reaction, these KIE values are in the range for PCET reactions involving phenol O–H(D) bond activation by metal–oxygen species. 71,72 …”

Copper–Oxygen Complexes Revisited: Structures, Spectroscopy, and Reactivity

“…337,338 Studies of 74 also show its O atoms to act as nucleophiles. 336 Thus, reaction of 74 with benzoyl chloride led to formation of benzoic acid, and examination of the kinetics of the reactions with a series of para -substituted benzoyl chlorides revealed a Hammett ρ = 2.5. On the other hand, examination of the kinetics of the reactions of 74 with phenols showed for R = H on the supporting ligand L23c , HAT occurred like what was seen for the bis( μ -oxo)dicopper species.…”

“…167,168,334–336 In one approach, a 1:1 metal/O 2 adduct was mixed with a second metal reagent (Figures 54 and 55). 167,334–336 Thus, reaction of the 1:1 Cu:O 2 adduct 3a (see Figure 5) with Ni(I) complex 70 ( L81 ) generated a mixture of 71 (major) and 72 (minor) (Figure 54), formulated as having the indicated isomeric cores on the basis of UV – vis, EPR, and resonance Raman spectroscopy [ ν (O – O) and [CuNi( μ -O) 2 ] 2+ core vibration at 847 and 625 cm −1 , respectively].…”

“…167,168,334–336 In one approach, a 1:1 metal/O 2 adduct was mixed with a second metal reagent (Figures 54 and 55). 167,334–336 Thus, reaction of the 1:1 Cu:O 2 adduct 3a (see Figure 5) with Ni(I) complex 70 ( L81 ) generated a mixture of 71 (major) and 72 (minor) (Figure 54), formulated as having the indicated isomeric cores on the basis of UV – vis, EPR, and resonance Raman spectroscopy [ ν (O – O) and [CuNi( μ -O) 2 ] 2+ core vibration at 847 and 625 cm −1 , respectively]. 167 An opposite route was taken in preparing compounds 73a – h and 74 , whereby a 1:1 M:O 2 adduct [for example, M = (Ph 3 P) 2 Pd or Pt, 334 or ( L2d )Ni 335 ] was treated with a Cu(I) complex of ligands L23c , L2d , L10a , L6a , or L20b (Figure 55).…”

From Enzymes to Functional Materials—Towards Activation of Small Molecules

“…[182] Furthermore, heterobimetallic complexes that contain metal-oxygenb ridges were recently shown to be powerful for hydrogen atom transfer reactions (HAT) from hydroxyl groups forming oxygen radicals ( Figure 14). [183,184] Notably,t he second metal center controlled the HATr eactivity of the complexes, showingadecrease in activity according to NiCu > NiNi > NiCo > NiFe. The changes were attributed to a Figure 13.…”