Ligand Effect on Reversible Conversion between Copper(I) and Bis(μ-oxo)dicopper(III) Complex with a Sterically Hindered Tetradentate Tripodal Ligand and Monooxygenase Activity of Bis(μ-oxo)dicopper(III) Complex

Abstract

A new sterically hindered tetradentate tripodal ligand (Me2-etpy) and its labeled analogue having deuterated methylene groups (d4-Me2-etpy) were synthesized, where Me2-etpy is bis(6-methyl-2-pyridylmethyl)(2-pyridylethyl)amine. Copper(I) complexes [Cu(Me2-etpy or d4-Me2-etpy)]+ (1 and 1-d4, respectively) reacted with dioxygen at -80 degrees C in acetone to give bis(mu-oxo)dicopper(III) complexes [Cu2(O)2(Me2-etpy or d4-Me2-etpy)2](2+) (1-oxo and 1-d4-oxo, respectively), the latter of which was crystallographically characterized. Unlike a bis(mu-oxo)dicopper(III) complex with a closely related Me2-tpa ligand having a 2-pyridylmethyl pendant, 1-oxo possessing a 2-pyridylethyl pendant is not fully formed even under 1 atm of O2 at -80 degrees C and is very reactive toward the oxidation of the supporting ligand. Thermal decomposition of 1-oxo gave an N-dealkylated ligand in yield approximately 80% based on a dimer and a corresponding aldehyde. The deuterated ligand d4-Me2-etpy greatly stabilizes the bis(mu-oxo)dicopper(III) complex 1-d4-oxo, indicating that the rate determining step of the N-dealkylation is the C-H bond cleavage from the methylene group. The reversible conversion between 1-d4 and 1-d4-oxo in acetone is dependent on the temperature, and the thermodynamic parameters (DeltaH and DeltaS) of the equilibrium were determined to be -53 +/- 2 kJ mol(-1) and -187 +/- 10 J mol(-1) K(-1), respectively. The effect of the 2-pyridylethyl pendant in comparison with the 2-pyridylmethyl and 6-methyl-2-pyridylmethyl pendants on the physicochemical properties of the copper(I) and bis(mu-oxo)dicopper(III) species is discussed.

L-Edge X-ray Absorption Spectroscopy and DFT Calculations on Cu2O2 Species: Direct Electrophilic Aromatic Attack by Side-on Peroxo Bridged Dicopper(II) Complexes

“…The cores are planar for all O species studied to date (Table S3). 21-23,36,69-74 A slight improvement in the bond lengths of the Cu 2 O 2 core (Cu ⋯ Cu, O ⋯ O, and Cu–O) is observed with 20-38% Hartree–Fock mixing. The experimental and calculated difference in the Cu ⋯ Cu and O ⋯ O distances along the series of differing HF mixing are within 0.05 Å and 0.03 Å, respectively, and smaller than the difference observed for the P complexes.…”

Theoretical Models on the Cu2O2 Torture Track: Mechanistic Implications for Oxytyrosinase and Small-Molecule Analogues

“…18,19 Although no X-ray crystal structure has yet been obtained for oxytyrosinase, spectral data for oxyhemocyanin and oxytyrosinase are sufficiently similar that there is little doubt that the resting state of oxytyrosinase also involves a side-on µ-η 2 :η 2 peroxo with five or six histidine ligands. 6 However, Tolman and co-workers, 11,13,17,20,21 and later others, [22][23][24][25][26] have demonstrated that in select instances the relative energies of isomeric µ-η 2 :η 2 peroxo and bis(µ-oxo) complexes can be sufficiently close to one another, and the barrier to their interconversion sufficiently low, that the two species may be in rapid equilibrium with one another; theoretical studies have rationalized many of the electronic structural details governing this phenomenon. [27][28][29][30][31][32][33][34] This observation potentially complicates mechanistic analysis in model systems and, by extension, oxytyrosinase, because the kinetics for systems characterized by a rapid preequilibrium can be indistinguishable from systems involving only a single reactant.…”

Synthesis, structure and dioxygen reactivity of a bis(µ-iodo)dicopper(i) complex supported by the [N-(3,5-di-tert-butyl-2-hydroxybenzyl)-N,N-di-(2-pyridylmethyl)]amine ligand

“…113.86 (8) between the phenolic protons and the amino nitrogen atoms (H1A · · · N3 1.961 Å ) were observed. The Cu · · · Cu separation was determined to be 2.9106(8) Å .…”