Aliphatic Hydroxylation by a Bis(μ-oxo)dicopper(III) Complex

Abstract

By using molecular oxygen bis(µ-oxo)dicopper(III) complexes can be produced from Cu(I) complexes with ligand L(X) (L(X)=p-substituted N-ethyl-N-[2-(2-pyridyl)ethyl]-2-phenylethylamine; X=OMe, Me, H, Cl, NO(2)) in which the benzylic position of the ligand is activated and hydroxylated by the Cu(2)O(2) core (see reaction scheme). Detailed characterization of this new C-H bond activation reaction by the bis(µ-oxo)dicopper(III) core reveals important information on the fundamental chemistry underlying copper monooxygenase reactivity.

Dinuclear copper–dioxygen intermediates supported by polyamine ligands

“…Namely, copper(I) complex of a tetradentate ligand such as TPA [tris(2-pyridylmethyl)amine] affords the end-on peroxo dicopper(II) complex (A) in the reaction with O 2 at a low temperature [6,29], 1;2 whereas the same reaction with a tridentate ligand such as N -alkyl-bis[2-(2-pyridyl)ethyl] amine derivative (Py2 R ) predominantly provides the side-on peroxo dicopper(II) complex (B) [5,8,30,31]. 3 Furthermore, we have recently demonstrated that oxygenation of copper(I) complexes supported by didentate ligands, N ; N -dialkyl-2-(2-pyridyl)ethylamine (Py1 R;R 0 ), affords not only the (l-g 2 :g 2 -peroxo)dicopper(II) complex (B) but also the bis(l-oxo)dicopper(III) complex (C) under the same experimental conditions [32,33]. These results stimulated us to investigate the dioxygenreactivity of dicopper(I) complexes unsymmetrically coordinated by a set of tetradentate (N 4 )/tridentate (N 3 ) and tridentate (N 3 )/didentate (N 2 ) metal binding units.…”

“…4, where a strong absorption band at 350 nm together with a shoulder around 400 nm and a very broad absorption band at 510 nm are observed. The absorption bands at 350 and 510 nm are very close to those of the (l-g 2 :g 2 - peroxo)dicopper(II) complex (B) [7,8,30] and the band at $400 nm is reminiscent of the bis(l-oxo)dicopper(III) complex (C) [11,12,32]. Resonance Raman spectra of the oxygenated solutions are shown in Fig.…”

“…The activation parameters were determined from the temperature dependence of the decomposition rate (Eyring plot, Fig. 6) as DH 6 ¼ ¼ 7:3 AE 0:5 kcal mol À1 and DS 6 ¼ ¼ À26:8 AE 1:9 cal K À1 mol À1 , which are fairly close to those of the aliphatic ligand hydroxylation reaction in the bis(l-oxo)dicopper(III) core supported by the 2-(2-pyridyl)ethylamine didentate ligand (DH 6 ¼ ¼ 9:3 AE 0:1 kcal mol À1 and DS 6 ¼ ¼ À17:4 AE 0:5 cal K À1 mol À1 ) [32]. Thus, the oxidative N-dealkylation reaction may proceed from the intermediate C, but not from B, via a hydrogen atom abstraction and oxygen rebound mechanism or its concerted variant as previously reported [32,38].…”

Complexes with FeIII2(μ-O)(μ-OH) Core Surrounded by Hydrogen-Bonding Interaction

“…17 The construction of highvalent M 2 (-O) 2 components is important as one of the motifs to construct a homogeneous catalyst, which activates oxygen molecule to oxidize the substrates. [18][19][20][21][22][23][24] In metalloproteins, hydrogen-bonding interaction sometimes occurs between an external molecule and the active site. For example, in myoglobin (Mb), which stores oxygen molecules in muscles, the distal histidine imidazole interacts to the dioxygen molecule bound to heme iron via hydrogen bonding.…”

Dinuclear chelates of acyclic and cyclic tridentate Schiff bases derived from sterically hindered o-aminophenols. A new type of reactivity of tridentate ligands under electrosynthesis conditions

“…The oxidative hydroxylation of aliphatic and aro matic fragments of the ligands in the presence of copper(II) ions was documented. 38, 39 It is suggested that the hydr oxylation occurs through the formation of the Cu II oxo dimer followed by the intramolecular nucleophilic attack of the oxygen atom of the bridging fragment on the carbon atom of the aliphatic or aromatic moieties of the mole cule. In our case, the formation of compounds 8 and 9 is most likely attributed to the conditions of the synthesis (electrochemical oxidation) and the presence of copper(II) ions in the reaction mixture.…”