Synthesis and Catalytic Reactivity of a Dicopper(II) μ-η²:η²-Peroxo Species Supported by 1,4,7-Tri-tert-butyl-1,4,7-triazacyclononane

Abstract

O2-derived Cu(n)O2 adducts are attractive targets for aerobic oxidation catalysis because of their remarkable reactivity, but oxidation of the supporting ligand limits catalytic turnover. We report that (t)Bu3tacn (1,4,7-tri-tert-butyl-1,4,7-triazacyclononane) supports a dicopper(II) μ-η(2):η(2)-peroxo species with the highest solution stability outside of an enzyme. Decomposition of this species proceeds without oxidation of the (t)Bu3tacn ligand. Additive-free catalytic aerobic oxidation reactions at or above room temperature are described, highlighting the potential of oxidatively robust ligands in aerobic copper catalysis.

Kinetic Investigation of the Reaction of Dioxygen with the Copper(I) Complex [Cu(PimiPr2)(CH3CN)]CF3SO3 {PimiPr2 = Tris[2‐(1,4‐diisopropylimidazolyl)]phosphine}

“…in our own work we could not detect any intermediate complex during the oxidation of a copper(I) complex with the ligand N,N' ‐bis[2‐(dimethylamino)ethyl] N,N ‐dimethylethane‐1,2‐diamine (Me 6 trien) in water in contrast to the reaction of hemocyanin with dioxygen , . However, the results of our analysis of the reaction of 1 with dioxygen together with a recent report on a quite stable copper peroxido complex in water are promising for finding a copper system that can be used in aqueous solutions for industrial applications of selective oxidations in the future. While it turned out that 1 is not suitable for the investigation of its reactivity with dioxygen in bubbly flows this is different for an iron peroxido complex reported by some of us previously.…”

“…However, no studies in protic solvents were performed with these complexes. Most recently a side‐on peroxido complex with a derivative of triazacyclononane (TACN) as a ligand was reported (using sterically demanding tert ‐butyl groups) which turned out to be quite stable in aqueous solutions . Still it was not possible to investigate its formation in protic solvents.…”

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

“…32 An especially stable ( μ - η 2 : η 2 -peroxo)dicopper complex was prepared using the extremely hindered ligand L20c ( t 1/2 = 14 h in MeOH, 9.6 days in aqueous Na 2 HPO 4 ), and its X-ray crystal structure was determined (Figure 35). 250 It exhibits a high ν (O–O) of 773 cm −1 indicative of a strong O–O bond and as a result of the high degree of steric bulk of the supporting ligand does not coexist with a bis( μ -oxo)dicopper isomer, like the system supported by L20b comprising i Pr rather than t Bu ligand substituents. 68,69 The complex effects the catalytic aerobic oxidation of 3,5-di- tert -butylcatechol to 3,5-di- tert -butylquinone and oxidation of benzyl alcohol to benzaldehyde.…”

“…Selected interatomic distances (Å): O1a-O1b = 1.475(4), Cu···Cu = 3.6349(8). Reprinted from ref 250. Copyright 2016 American Chemical Society.…”

High-valent copper in biomimetic and biological oxidations

“…This isomeric interconversion involves the forming and breaking of the O-O bond with concurrent reduction and oxidation of the Cu(III) and Cu(II) centers, respectively [16,76]. Oxygenation of the more sterically demanding [(tBu 3 TACN)Cu(I)(MeCN)] + yields exclusively a S P species [73,77]. Thus, the variation of the alkyl substituents on the TACN ligand backbone from Me [78] to t Bu [73] generates optically pure O to S P species, respectively, illustrating a ligand steric continuum resulting in a Cu-O 2 speciation change.…”