New Oxidovanadium(IV) Complexes with 2,2′-bipyridine and 1,10-phenathroline Ligands: Synthesis, Structure and High Catalytic Activity in Oxidations of Alkanes and Alcohols with Peroxides

Abstract

Reactions of [VCl3(thf)3] or VBr3 with 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen) in a 1:1 molar ratio in air under solventothermal conditions has afforded polymeric oxidovanadium(IV) four complexes 1–4 of a general formula [VO(L)X2]n (L = bpy, phen and X = Cl, Br). Monomeric complex [VO(DMF)(phen)Br2] (4a) has been obtained by the treatment of compound 4 with DMF. The complexes were characterized by IR spectroscopy and elemental analysis. The crystal structures of 3 and 4a were determined by an X-ray diffraction (XRD) analysis. The {VOBr2(bpy)} fragments in 3 form infinite chains due to the V = O…V interactions. The vanadium atom has a distorted octahedral coordination environment. Complexes 1–4 have been tested as catalysts in the homogeneous oxidation of alkanes (to produce corresponding alkyl hydroperoxides which can be easily reduced to alcohols by PPh3) and alcohols (to corresponding ketones) with H2O2 or tert-butyl hydroperoxide in MeCN. Compound 1 exhibited the highest activity. The mechanism of alkane oxidation was established using experimental selectivity and kinetic data and theoretical DFT calculations. The mechanism is of the Fenton type involving the generation of HO• radicals.

Metal Complexes Containing Redox-Active Ligands in Oxidation of Hydrocarbons and Alcohols: A Review

“…The proposed model is also in agreement with the experimental data. Gushchin, Kuznetsov, et al recently [84,85] observed high activity among the vanadium complexes shown in Scheme 5 in the oxidation of hydrocarbons with peroxides. The mechanism for the generation of OH radicals is presented in Scheme 6.…”

“…Machura et al [79] described the oxidation of inert alkanes to alkyl hydroperoxides by H2O2 catalyzed with monomeric oxovanadium(V) complexes of 8-hydroxyquinoline derivatives as noninnocent ligands (Scheme 4). The analogous ligands in complexes with copper or rhenium were used in oxidations by peroxides [80][81][82][83] Gushchin, Kuznetsov, et al recently [84,85] observed high activity among the vanadium complexes shown in Scheme 5 in the oxidation of hydrocarbons with peroxides. The mechanism for the generation of OH radicals is presented in Scheme 6.…”

An oxidovanadium(IV) complex with 4,4′-di-tert-butyl-2,2′-bipyridine ligand: Synthesis, structure and catalyzed cyclooctene epoxidation

“…The title complex was synthesized from vanadium(III) chloride (VCl3) and 4,4'-di-tertbutyl-2,2'-bipyridine (dbbpy), with concomitant oxidation in air to give the {V=O} 2+ moiety, see Scheme 1. The same synthetic procedure was previously used for the preparation of other oxidovanadium(IV) complexes with 2,2'-bipyridine, 1,10-phenathroline [31], bis(N-(2,6diisopropylphenyl)-imino)acenaphthene (dpp-bian) [10], dehydrophenanthroline and diazofluorene ligands [42]. The reaction of VCl3 with 4,4'-di-tert-butyl-2,2'-bipyridine (dbbpy) The IR spectrum of 1 shows a strong band at 989 cm -1 , assigned to a V=O stretching mode in agreement with those reported for other oxidovanadium(IV) complexes [10,[44][45][46].…”

“…Our recent studies have shown that oxovanadium(IV) complexes with redox-active diimine ligands exhibit high catalytic activity towards alkanes and alcohols oxygenation with H2O2 or tert-butyl hydroperoxide in MeCN. In particular, the square-pyramidal oxidovanadium (IV) complex [VOCl2(dpp-bian)] (dpp-bian = bis[N-(2,6-diisopropylphenyl)imino]acenaphthene) [10] and polymeric complexes of general formula [VO(L)X2]n (L = bpy, phen and X = Cl, Br) [31] were synthesized and tested as oxidation catalysts. In this framework, we report herein further results on the preparation of a novel octahedral oxidovanadium(IV) complex [VOCl2(dbbpy)(H2O)] (1), as well as its catalytic properties in the cyclooctene oxidation with tert-butyl hydroperoxide in CHCl3, which is another commonly used solvent for catalyzed oxidations.…”

Highlights of the Most Cited Papers in the Section “Catalysis in Organic and Polymer Chemistry”

“…Another topic of relevance is the oxidation of organic molecules: in particular, in two highly cited articles, Gushchin, Bilyachenko, Shul'pin, and coworkers presented efficient procedures for the conversion of alkanes and alcohols into alcohols and ketones, respectively, employing peroxides as oxidants (H 2 O 2 or t BuOOH). The catalytic systems employed were composed of new polymeric oxovanadium(IV) complexes of general composition [VO(L)X 2 ] n (X = Cl or Br; L = 2,2 -bipyridine or 1,10-phenanthroline) [8] [9]. In both works, complete details on the structure and mechanism of action of these new catalysts are given.…”