Dioxygen Reactivity of New Bispidine-Copper Complexes

Abstract

The reactivity of copper complexes of three different 2nd generation bispidine-based ligands (bispidine = 3,7-diazabicyclo[3.3.1]nonane; mono- and bis-tetradentate; exclusively tertiary amine donors) with dioxygen [(reversible) binding of dioxygen by copper(I)] is reported. The UV-vis, electrospray ionization mass spectra (ESI-MS), electron paramagnetic resonance (EPR) and vibrational spectra (resonance Raman,rR) of the dioxygen adducts indicate that, depending on the ligand and reaction conditions, several different species (mono- and dinuclear, superoxo, peroxo and hydroperoxo), partially in equilibrium with each other, are formed. Minor changes in the ligand structure and/or experimental conditions (solvent, temperature, relative concentrations) allow switching between the different forms. With one of the ligands, an end-on-peroxo-dicopper(II) and a mononuclear copper(II)-hydroperoxo complex could be characterized. With another ligand, reversible dioxygen binding was observed, leading to a meta-stable copper(II)-superoxo complex, and the amount of dioxygen involved in the reversible binding to CuI was determined quantitatively. The mechanism of dioxygen binding as well as the preference of each of the three ligands for a particular dioxygen adduct is discussed on the basis of a computational (DFT) analysis.

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

“…175,179–195,200–210 Notably, these complexes show a diagnostic UV–vis feature at ~350 nm assigned as a peroxide→ Cu(II) ligand-to-metal charge transfer (LMCT) transition. In general, this absorption is observed at higher energy and intensity for R = H than for R = alkyl.…”

“…145,340 Key spectroscopic properties of such complexes, mostly reported since 2004, are presented in Table 7. 128,144,200,341–346 They have in common the typical, previously analyzed 347 signatures comprising (1) peroxide π *→ Cu(II) d LMCT features at 530 – 550 nm (~10,000 M −1 cm −1 ) and 600 nm (sh) and (2) characteristic resonance Raman stretching frequencies for ν (O – O) and ν (Cu – O) at ~800 – 850 cm −1 and ~550 cm −1 , respectively. Slight variations evaluated through detailed comparisons with the parent L41a system have provided insights into geometric differences or donor atom effects.…”

“…317 Differences in steric effects also were proposed to underlie the different course of oxygenations of Cu(I) complexes of bispidine derivatives L31a and L31b ; only 1:1 Cu:O 2 adduct formation was seen for L31b , whereas L31a supported a ( trans -1,2-peroxo)dicopper complex. 200 …”

Transition Metal Complexes and the Activation of Dioxygen

“…These electrophilic hydroxylations are unusual for such end-on peroxo cores, which typically act as nucleophiles instead [339]. In addition, (μ-η 1 :η 1 -peroxo)dicopper cores were implicated in oxygenation reactions of Cu(I) complexes of bispidine ligands 106 [348] and 107 [349], and the pathway for catecholase activity of such oxygenated complexes was evaluated by theory [349].…”

Eccentricities in Spectroscopy and Reactivity of Non‐Heme Metal Intermediates Contained in Bispidine Scaffolds

“…Inorganic chemists were looking at it as a chelating ligand -where it can provide a suitable cavity for encapsulating several metal ions like iron, copper, vanadium, ruthenium, palladium, etc. [36][37][38][39][40][41][42][43][44][45][46] Whereas organic and biological researchers employed this molecule as a synthon for potential biomolecules. [47,48,50,51] Moreover, this molecule is enriched with intrinsic handles of substitution whereby one can tune its basicity and bite angles during complexation with a metal ion.…”