Liquid-phase oxidation of dibenzyl ether by atmospheric oxygen in the presence of homo- and heteroligand pivalate and 3,5-dimethylpyrazolate complexes of 3d metals

Abstract

The main products of the reaction in the presence of homo-and heteroligand pivalate and 3,5-dimethylpyrazolate mono-, bi-, and trinuclear complexes of Co, Cu, Ni, and Zn are the hydroperoxide, benzaldehyde, and benzoic acid. The effect of the composition and structure of the complexes on the conversion of the substrate, the selectivity of the process, and the possibility of alternative routes to the oxidation of dibenzyl ether is discussed.Metal carboxylates are some of the best known and most widespread classes of coordination compounds, the variety of which is due to the broad possibilities of the structural function of the polydentate ligand RCOO - [1]. It is this specific characteristic that makes it possible to vary the composition and structure of carboxylate complexes, leading on the one hand to the unusual characteristics (catalytic, magnetic, etc.) of such compounds (e.g., see [2,3]) and on the other to the possibility of using them as "platforms" for the production of the metal complexes regarded as synthetic analogs of the active part of metalloenzymes [4][5][6].Thus, the authors of [7-11] developed approaches to the synthesis of a similar series of pivalate complexes of zinc, copper, nickel, and cobalt containing coordinated 3,5-dimethylpyrazole (Hdmpz), which models the histidine fragment in the enzyme part of metalloenzymes.In a continuation of our investigations into the catalytic properties of the polynuclear carboxylates of 3d metals in the liquid-phase oxidation of compounds with activated CH bonds [e.g., dibenzyl ether (DBE) [12]] by atmospheric oxygen (and then by air) in the present article features of the oxidation of DBE in the presence of complexes (mainly bi-and trinuclear complexes) of cobalt, copper, nickel, and zinc, in which the metal cores are formed by pivalate (ì-Piv) or 3,5-pyrazolate (ì-dmpz) bridging ligands, are discussed. As seen from Table 1, the terminal ligands in these complexes are either neutral 0040-5760/09/4506-0355

Formation of the unusual cluster Cu4(μ4-OH)(μ-(CF3)2pz)4(μ-OOCPh)2(μ-OH)2(OH2)(Et3NH)[O(CH2Ph)2]2 in the thermolysis of a copper μ-aqua complex with bridging pyrazolate and acetate ligands in dibenzyl ether in the presence of atmospheric oxygen

“…A similar trend is characteristic of homo and het eroleptic 3d metal pivalates and 3,5 dimethylpyra zolates [2]. In the presence of these complexes (for the DBE conversion ≤ 25%), the sequence of DBE trans formations can be represented as follows:…”

“…It is not improbable that complexes of the type 3 can be intermediates in the liquid phase oxidation of DBE with atmospheric oxygen in the presence of copper complexes containing pyrazolate bridges (see, e.g., [2]). …”

“…X ray diffraction studies were carried out on a Bruker SMART Apex II automated diffractometer equipped with a CCD detector (MoK α radiation, graphite monochromator, ω scan mode) according to (2). 3,5 Bis(trifluoromethyl)pyrazole (0.1 g, 0.33 mmol) was added to a suspension of Cu 2 (OOCMe) 4 (OH 2 ) 2 (0.1 g, 0.24 mmol) in CHCl 3 (20 mL) in the presence of Et 3 N (1 mL).…”

“…(2) In [2], it has been found that the presence of cobalt complexes makes the process more selective for BAld (up to 60%), while DBE oxidates obtained in the pres ence of copper complexes mainly contain HP. In addi tion, copper complexes favor deeper oxidation of DBE (into BAc) than do cobalt complexes.…”