Jarosław M. Sobczak

The catalytic epoxidation of olefins with organic hydroperoxides

Abstract The metal catalyzed epoxidation reaction of olefins with organic hydroperoxides appeared to be particularly important not only from an industrial point of view (Halcon process) but also because of its wide application in synthetic organic chemistry. The number of catalytic systems containing transition metal complexes is considered, and the correlations between the structure and the reactivity of olefins and hydroperoxide are discussed. The mechanism of the catalytic epoxidation reaction is considered on the basis of an analogy with the noncatalytic epoxidation reaction and that with peracids. The function of the catalyst and the role of its transient forms, including the effect of solvent in the catalytic reaction, are discussed.

New insights into the chemistry of oxomolybdenum(VI) complexes with N-salicylidene-2-aminoethanol

Abstract Oxomolybdenum(VI) complexes with tridentate Schiff base, N -salicylidene-2-aminoethanol (H 2 sae), has been synthesised by the reaction of Mo(O) 2 (sal) 2 (where Hsal=salicylic aldehyde) with 2-aminoethanol. This reaction leads to dimeric [MoO(μ-O)(sae)] 2 and new monomeric [Mo(O) 2 (sae){1,2-O (−) C 6 H 4 C(H)N (+) (H)C 2 H 4 OH}] ( 1 ) compounds. Also substitution of acetylacetonate ligand in Mo(O) 2 (acac) 2 by H 2 sae in EtOH leads to the same complexes (vide infra), but in MeOH monomeric compound Mo(O) 2 (sae)(MeOH) ( 2 ) was formed. The molecular structure of complexes 1 and 2 have been determined by X-ray studies, which confirm that one of the H 2 sae co-ordinates as η 3 -tridentate O,N,O′ ligand, while in complex 1 this ligand exists also in zwitterionic form with intramolecular hydrogen bonding, O⋯HN, 2.584(3) A, of phenolic oxygen bonded to the molybdenum atom. The crystals of 1 are triclinic, space group P 1 , a =8.483(2) A, b =10.187(3) A, c =11.034(3) A, α =105.26(2)°, β =95.29(2)°, γ =95.10(2)°, and D calcd =1.666(1) g cm −3 for Z =2. The crystals of 2 are monoclinic, space group P 2 1 / c , a =6.697(2) A, b =7.375(2) A, c =24.100(3) A, β =92.76(5)°, and D calcd =1.805(1) g cm −3 for Z =4.

New efficient aerobic oxidation of some alcohols with dioxygen catalysed by N-hydroxyphtalimide with vanadium co-catalysts

New efficient vanadium co-catalysts have been developed for the oxidation of some alcohols with O(2) catalysed by N-hydroxyphthalimide (NHPI). Various alcohols (primary and secondary) were selectively oxidized by O(2) under mild conditions in the presence of a catalytic amount of NHPI as a radical-producing agent combined with small amounts of vanadium complexes with or without the addition of a simple salt (e.g. LiCl) or base (e.g. pyridine).

Copper(II) binding by kanamycin A and hydrogen peroxide activation by resulting complexes

Protonation and copper(II) coordination properties of kanamycin A were studied in solution by potentiometry, UV-Vis, circular dichroism (CD), EPR and cyclic voltammetry (CV). Only mononuclear complexes of stoichiometries ranging from CuH2L to CuH−2L were found. Kanamycin A anchors Cu(II) ions with an {NH2, O−} chelate of the C-ring of its molecule. At pH higher than 6 the amino and hydroxyl groups of the A-ring of kanamycin A also participate in binding. The resulting structure, similar to that of complexes of other unsubstituted aminoglycosides studied previously, involves Cu(II) coordination by donors of terminal aminosugar rings, rather than those of the central unit. The results of cyclic voltammetry investigations, kinetic studies of H2O2 disproportionation and ROS detection experiments, further supported the mechanism of oxidative reactivity of cupric complexes of aminoglycosides, proposed by us recently [M. Jezowska-Bojczuk, W. Leśniak, W. Bal, H. Kozlowski, K. Gatner, A. Jezierski, J. Sobczak, S. Mangani and W. Meyer-Klaucke; Chem. Res. Toxicol., 2001, 14, 1353–1362], which involves Cu(I) and Cu(III) redox states and both metal-bound and free ROS.

The molybdenum(V) complexes as the homogeneous and heterogenized catalysts in epoxidation reactions of olefins with the organic hydroperoxides

Abstract The catalytic properties of new Mo(V) complexes with ligands such as ethylene glycol, lactic acid and amygdalic acid in homogeneous systems, as well as the properties of the heterogenized catalysts obtained in the ionic exchange reaction of the complex Na2[Mo2O4(OX)2(H2O)2]·3H2O with Castel A-500p, Dowex 1X8, and Wofatit AD-41 anionites, were examined. The catalysts obtained are active in epoxidation reactions of olefins with organic hydroperoxides. The structure of the heterogenized catalysts is discussed, the catalyst changes during the epoxidation reaction are interpreted, and the correlation between the structure and reactivity of the homogeneous and heterogenized catalysts is considered on the basis of the i.r. spectra.

Aerobic oxidation of alcohols and alkylaromatics with dioxygen catalysed by N-hydroxyphthalimide with vanadium co-catalysts

[Bu4N]VO3 or a combination of vanadium complexes with chloride salts are attractive co-catalysts for oxidation reactions of organic compounds with dioxygen catalysed by N-hydroxyphthalimide. The role of the chloride additive relates to the formation of more labile six-coordinate vanadium complexes. The same effect is also observed with amines. Two catalytic systems based on NHPI/VO(acac)2 with LiCl or [Bu4N]Cl and NHPI/[Bu4N]VO3 are most effective in oxidation reactions of primary and secondary alcohols, but oxidation of alkylaromatics proceeds with conversion rates of from 14.4% in the case of toluene to 67.0% in the case of ethylbenzene and with different selectivities, dependent on the structure of the substrate.

The structure of binuclear molybdenum(VI) oxocomplexes with dianionic tridentate Schiff bases

SummaryThe new MoVI complex [Mo(O) (μ-O) (SAE)]2 was prepared and characterized by means of spectroscopic (i.r.,1Hn.m.r.) and crystallographic measurements. Crystals of the [Mo(C9H8NO2)(H2O)]2, M=582.3, orthorhombic, space group Pbca,a=13.108(4),b=8.982(2),c=16.842(4) Å, v=1982.9 Å3, z=4, Dm=1.93(2), Dc=1.95 g cm−3, MoKα γ=0.71069 Å, μ=1.3 mm−1, F(000)=1152, T=295K, R=0.035 for 2413 reflections.The crystal structure consists of [Mo(O)(μ-O)(L)]2, in dimeric units. The coordination geometry around each molybdenum atom is distorted octahedral with Mo−O (terminal) and Mo−O (bridge) distances of 1.694(3) and 1.760(3) Å, respectively, and with the angle O(1)−Mo−O(2) of 105.6(1)o, typical for manycis-dioxocomplexes of MoVI. The asymmetric bridge is characterized by the following parameters: Mo−O(2)i and Mo−Moi distances equal 2.408(3) and 3.319(3) Å, respectively, and the Mo−O(2)−Moi and O(2)−Mo−O(2)i angles equal 104.5(1)o and 75.5(1)o, respectively.The i. r. and Raman spectra of molybdenum complexes with an asymmetric double oxygen bridge display a strong absorption the 800–850 cm−1 range.

Catalytic oxidative dehydrogenation of cyclohexene

Oxidation of cyclohexene, in the presence of a palladium catalyst and anthraquinone-2-sulfonic acid, sodium salt (AMS) as cocatalyst, has been shown to yield selectively benzene. The oxidative dehydrogenation reaction proceeds in the liquid phase under atmospheric molecular oxygen pressure. Palladium dichloride and palladium on charcoal, combined with AMS, are the catalyst systems which show optimum conversion of cyclohexene (85–100%) and selectivity to benzene (92–100%).

Catalytic activity of molybdenum(V) BIS(diphenylphosphine)ethane complexes in epoxidation reaction

Abstract The catalytic activity of complexes (dppeH 2 )[MoOCl 5 ], MoOCl 3 (dppe) — red and brown isomers — and of Mo 2 O 2.5 Cl 5 (dppe) 2 (where dppe: bis-(diphenylphosphine)ethane) in the decomposition of cumene hydroperoxide and in cyclohexene epoxidation has been examined. Except for the Mo 2 O 2.5 − Cl 5 (dppe) 2 complex, the other compounds catalyse the ROOH decomposition and undergo deactivation during the reaction. A dark-brown precipitate settled in the post-reaction mixture. The precipitate was carefully examined and the results revealed the complete destruction of the initial molybdenum catalyst in the cumene hydroperoxide decomposition process. The molybdenum(V) oxocomplexes proved to be very good and interesting catalysts for the epoxidation of olefins with organic hydroperoxides. The results of kinetic investigations of the epoxidation reaction and of the changes in catalyst structure in that process are presented in this paper.

Catalytic activity of Mo(NO)2(HSO4)2L2 and [Mo(NO)2L4](HSO4)2 (L=MeCN, EtOH) in reaction of metathesis and epoxidation of olefins

Abstract The dinitrosylmolybdenum complexes Mo(NO) 2 (HSO 4 ) 2 L 2 and [Mo(NO) 2 L 4 ](HSO 4 ) 2 (L=MeCN, EtOH) are reported and their use as precatalysts in the presence of ethylaluminium-dichloride for metathesis of olefins discussed. Upon treatment with EtAlCl 2 the formation of an alkilidenemolybdenum complexes has been observed, isolated and spectroscopically characterized. The title complexes (for L=MeCN) are also precursors of very effective catalysts of the organic hydroperoxide decomposition and olefine epoxidation reactions. The metathesis as well as epoxidation data indicate an important influence of the ligand sphere of the catalysts on their activity and product distribution.