Giulia Licini

Liquid phase oxidation reactions by peroxides in the presence of vanadium complexes

Abstract The reaction of vanadium (V) derivatives with hydrogen peroxide or with alkyl hydroperoxides leads to peroxovanadium complexes which are effective and selective oxidants of organic and inorganic substrates either under stoichiometric or catalytic conditions. Examples of synthetically significant oxidations of various classes of organic compounds are reported together with details on the commonly accepted mechanisms operating. When possible a comparison is made between peroxovanadium complexes of other do metal derivative, e.g. Ti(IV), Mo(VI) and W(VI).

The medicinal and catalytic potential of model complexes of vanadate-dependent haloperoxidases

Abstract Vanadium(V) complexes predominantly of composition VO( O 3 N ), modeling the active center of vanadate-dependent haloperoxidases, are investigated with respect to (i) their catalytic potential in enantio-selective oxidation by peroxide of prochiral sulfides, and (ii) their in vitro cytotoxicity and insulin-mimetic ability towards fibroblast cell cultures. The peroxidation of methyl-tolylsulfide with cumyl-hydroperoxide, which is related to the sulfideperoxidase activity of haloperoxidases, is catalyzed by ( RRR )-[VO(OMe)L] [H 2 L=( R , R )-bis(2-phenylethanol)-( R )-1-phenylethylamine] as well as by a mixture of [VO(O i Pr) 3 ] and H 2 L to an enantiomeric excess (ee) of 25%. The crystal and molecular structures of ( RRR )-[VO(OMe)L] · 1/2MeOH are reported. In the context of the phosphatase activity of the apo-haloperoxidases, possible modes of action of vanadium compounds in insulin-mimesis are addressed. In vitro results for seven oxovanadium(IV) and -(V) coordination compounds show that, at essentially non-toxic concentrations [ c (V)

C3 Vanadium(V) Amine Triphenolate Complexes: Vanadium Haloperoxidase Structural and Functional Models

The C 3 vanadium(V) amine triphenolate complex 1f has been characterized as a structural and functional model of vanadium haloperoxidases. The complex catalyzes efficiently sulfoxidations at room temperature using hydrogen peroxide as the terminal oxidant, yielding the corresponding sulfoxides in quantitative yields and high selectivities (catalyst loading down to 0.01%, TONs up to 9900, and TOFs up to 8000 h (-1)) as well as bromination of 1,3,5-trimethoxybenzene (catalyst loading down to 0.05%, TONs up to 1260, and TOFs up to 220 h (-1)).

Asymmetric oxidation of 1,3-dithiolanes. A route to the optical resolution of carbonyl compounds

Abstract The asymmetric oxidation ( t -BuO 2 H, Ti(OPr- i ) 4 , DET) of a series of 1,3-dithiolanes was carried out to produce the corresponding S-oxides with high chemical and optical yields. By contrast, the oxidation of 1,3-dithianes and 1,3-oxathiolane prepared from the same carbonyl compounds gave much lower optical yields. The optical resolution of the model ketone, dl-menthone, via a) 1,3-dithiolane formation b) asymmetric S-oxidation c) chromatographic diasteromeric separation d) regeneration of the carbonyl group, (93% optical yield), is described.

Reactivity control in iron(III) amino triphenolate complexes: comparison of monomeric and dimeric complexes.

Iron(III) amino triphenolate complexes with different substituents in the ortho-position of the phenolate moiety (R = H, Me, tBu, or Ph) have been synthesized by the reaction of iron(III) chloride and the sodium salt (Na(3)L(R)) of the requisite ligand. The complexes have been shown to be of either monomeric ([FeL(R)(THF)]) or dimeric ([FeL(R)](2)) nature by a combination of X-ray diffraction, (1)H NMR, solution magnetic susceptibility, and cyclic voltammetry studies. These analytical studies have shown that the monomeric and dimeric [FeL(R)] complexes behave distinctively, and that the dimer stability is a function of the ortho-positioned groups. Both the dimeric as well as monomeric complexes were tested as catalysts for the catalytic cycloaddition of carbon dioxide to oxiranes, and the data show that the monomeric complexes are able to mediate this conversion with significantly higher activities than the dimeric complexes. This difference in reactivity is controlled by the substitution pattern on the ligand L(R), and is in line with the catalytic requisite of binding of the epoxide substrate by the iron(III) center.

Ti(IV)-amino triphenolate complexes as effective catalysts for sulfoxidation

C(3)-symmetric Ti(IV) amino triphenolate complexes efficiently catalyze, without previous activation and in excellent yields, the oxidation of sulfides at room temperature, using both CHP and the more environment friendly aqueous hydrogen peroxide as terminal oxidants, with catalyst loadings down to 0.01%. The Ti(IV) catalysts and the intermediate Ti(IV)-peroxo complexes have been characterized in solution by (1)H NMR and ESI-MS techniques and via density functional studies.

Enantioselective oxidation of thioethers1: An easy route to enantiopure C2 symmetrical bis-methylsulfinylbenzenes

The direct oxidation of bis-methylthioethers 1 by t-butyl hydroperoxide, titanium tetra-iso-propilate and (+)-diethyltartrate, affords the almost enantiomerically pure dl bis-methylsulfinylbenzenes 2 (e.e.⩾99%) in a process which is also characterized by a very high diastereoselectivity.

Asymmetric oxidation of thioethers. Optical resolution of [1,1′-binaphthalene]-2,2′-dithiol☆

Almost optically pure (e.e. > 98%) [1,1′-binaphthalene]-2,2′-dithiol (2) is obtained by resolution of racemic 2 via the transformation of the sulfidryl functions into the corresponding thioethers 3 which are asymmetrically oxidized to diastereomeric chiral monosulfoxides 4 and then reconverted into 2. The diastereo and enantioselectivity is dependent on the structure of the thioether; i.e. the dimethylthioether 3a gives two diastereomeric sulfoxides 4a in ca. 1:1 ratio, each of them in > 98% e.e., while cyclic dithioethers 3b–d afford a single diastereomeric sulfoxide 4b–d in 46–78% e.e..

A ‘waterproof’ catalyst for the oxidation of secondary amines to nitrones with alkyl hydroperoxides

Abstract Catalytic oxidation of secondary amines to nitrones using alkyl hydroperoxides as primary oxidant has been demonstrated for the first time. The titanium alkoxide catalyst is protected from co-product water by the combined use of a tightly binding trialkanolamine ligand and molecular sieves. Nitrones can be obtained in high yield (up to 98%) under homogeneous, anhydrous conditions and even in the absence of solvent. The reactions are fast (2–7 h) and good selectivity can be achieved with as little as 1% catalyst.

Stereoselective Control by Face‐to‐Face Versus Edge‐to‐Face Aromatic Interactions: The Case of C3‐TiIV Amino Trialkolate Sulfoxidation Catalysts

The stereoselective oxidation of differently functionalised benzyl phenyl sulfides has been examined by using enantiopure Ti(IV) trialkanolamine complexes. These complexes efficiently catalyse the sulfoxidation with good stereoselectivities. The data highlight the contribution to the stereoselectivity of steric effects and non-covalent pi-pi interactions between the aromatic rings of the Ti(IV) complex and those pertaining to the substrates. Enantiomeric excesses have been correlated with the electrostatic potential surfaces (EPS) of the reacting sulfides. The overall study leads to a mechanistic interpretation that explains the stereoselectivity of the system and dissects the role of aromatic and steric interactions in the stereoselective process.