Fernando Montanari

PERFLUOROCARBON-SOLUBLE CATALYSTS AND REAGENTS AND THE APPLICATION OF FBS (FLUOROUS BIPHASE SYSTEM) TO ORGANIC SYNTHESIS

Abstract The new phase-separation and immobilization technique known as FBS (fluorous biphase system) is becoming more and more popular among researchers in both industry and academia. The immiscibility of perfluorocarbons with most organic solvents and water is of great advantage, in that it allows the easy recovery and recycling of the catalysts and reagents. The major results so far obtained in this field are discussed.

Synthesis of perfluoroalkylated bipyridines — New ligands for oxidation reactions under fluorous triphasic conditions

Abstract Fluorous soluble bipyridines bearing two perfluoroalkylated side chains in the 6,6′- or 4,4′-positions have been prepared in good yields via etherification of 6,6′-bis(chloromethyl)-2,2′-bipyridine or C -alkylation of 6,6′-dimethyl-2,2′-bipyridine. The new ligands L exhibit amphiphilic behaviour with respect to certain fluorous-organic biphasic systems. Nevertheless, their ruthenium complexes (RuL n )X generated in situ are efficient catalysts for the epoxidation of trans -stilbene in a fluorous triphasic system CH 2 Cl 2 /H 2 O/C 8 F 18 in the presence of NaIO 4 . The fluorous phase, where (RuL n )X is trapped, can be used up to four times without major loss of catalytic activity.

Oxidations catalyzed by stable metallo-tetraaryl porphyrins under aqueous-organic two-phase conditions

Oxydation du cyclooctene catalysee par des complexes Mn(III) tetraaryl-5,10,15,20 porphyrines

Porphyrins and azaporphines as catalysts in alkene epoxidations with peracetic acid

the reactivities of five MnIII(Cl) - porphinoids were compared in the catalytic alkene epoxidations in CH3CN solution with peracetic acid as primary oxidant. Porphyrins 1 and 2 bearing Cl and NO2 substituents showed the best efficiency while tetraazaporphyrin 5 was found to be an interesting catalyst for terminal alkene epoxidations.

Asymmetric Epoxidation of Alkenes in Fluorinated Media, Catalyzed by Second-Generation Fluorous Chiral (Salen)manganese Complexes

The synthesis of sterically hindered chiral (salen)manganese complexes bearing perfluoroalkyl ponytails and their use in asymmetric epoxidation reactions are described. For better understanding of the relative influences of steric and electronic effects on the enantioselectivity of the fluorous catalysts, the epoxidation of 1,2-dihydronaphthalene and benzosuberene was first studied under homogeneous conditions. It was shown that the presence of sterically demanding tert-butyl groups and, to a lesser degree, the displacement of the electron-withdrawing perfluoroalkyl substituents from the ligand core provide ees higher than those attainable with first generation fluorous chiral (salen)manganese complexes featuring perfluoroalkyl substituents in the key positions (3,3′ and 5,5′) in the ligand. Second generation catalysts (Mn-6)C7F15COO and (Mn-7)C7F15COO were successfully employed in the fluorous biphase epoxidation of alkenes with PhIO as the oxidant and pyridine N-oxide as an additive. Epoxide yields (68−98%) and ees (50−92%) were similar to those obtained with the same oxidizing system and standard (salen)manganese complexes under homogeneous conditions. When the reaction was complete, the fluorous layer in which the catalyst was immobilized was easily recoverable by simple phase separation at room temperature and could be used up to three times before significant decline in yield and enantioselectivity was observed.

Towards epoxidation catalysts for fluorous biphase systems: Synthesis and properties of two Mn(III)-tetraarylporphyrins bearing perfluoroalkylamido tails

Abstract Two new Mn(III)-tetraarylporphyrins Mn-1 and Mn-2 bearing one amido-bonded n-C7F15 chain on each meso-aryl group have been synthesized. The presence of four perfluoroalkyl tails strongly influences the solubility of these compounds in common organic solvents, but it is not sufficient to impart solubility in fluorocarbons. The catalytic activity of the new complexes was tested in alkene epoxidations employing aqueous NaOCl as oxygen donor. Results show that Mn-2 is more active than Mn(III)-5,10,15,20-tetrakis-(2,6-dichlorophenyl)porphyrin, one of the most efficient porphyrinic catalysts for hydrocarbon oxygenation.

Synthesis of chiral Mn(III)-meso-tetrakis-[2.2]-p-cyclophanyl-porphyrin: a new catalyst for enantioselective epoxidation

Abstract The synthesis of Mn(III)-complexes of new chiral porphyrins 1a and 1b prepared by condensation of enantiomerically pure [2.2]- p -cyclophane-4-carbaldehyde and pyrrole are described. These compounds were used as catalysts in epoxidation reactions of prochiral alkenes, carried out in the presence of aqueous NaOCl at pH = 10.0 as oxygen donor and small amounts of 4-tert-butylpyridine as axial ligand, in CH 2 Cl 2 H 2 O two-phase conditions at 0°C. Results indicate a satisfactory catalytic efficiency (up to 700 overall turnovers), with enantiomeric excesses in the range 22–31%.

Epoxidation of Alkenes Under Liquid-Liquid Biphasic Conditions: Synthesis and Catalytic Activity of Mn(III)-Tetraarylporphyrins Bearing Perfluoroalkyl Tails.

Abstract Four tetraarylporphyrins bearing one n-C8F17 chain on each meso-aryl group have been synthesized. The Mn(III)-complexes of these new compounds (Mn-1 - Mn-4) were used as catalysts in alkene epoxidations carried out under aqueous-organic biphasic conditions. High epoxide yields were obtained with catalysts in which, along with perfluoroalkyl chains, bulky substituents were present at appropriate positions. The expected general enhancement of stability and catalytic activity due to the electron-withdrawing effect of n-C8F17 substituents was not observed. However, Mn-4 was found to be an exceptionally active catalyst for NaOCl promoted epoxidation of poorly reactive linear α-alkenes.

Hydroxymethyl 18-crown-6 and hydroxymethyl [2.2.2]cryptand: versatile derivatives for binding the two polyethers to lipophilic chains and to polymer matrices

Abstract The presence of the hydroxymethyl group allows facile functionalisation of 18-crown-6 and of [2.2.2]cryptand. A variety of lipophilic and polymer-supported macrocyclic polyethers is thus available. They are efficient and easily recyclable phase-transfer catalysts.

Biomimetic models of cytochrome P-450. A doubly tailed manganese(III)–tetraaryl porphyrin; an extremely efficient catalyst for hydrocarbon oxygenations promoted by 30% H2O2

MnIII–porphyrin 1, bearing an imidazole axial ligand and a carboxylic group juxtaposed on opposite sides of the porphyrin plane, is an extremely efficient catalyst for the activation of 30% H2O2 in hydrocarbon oxygenations carried out in CH2Cl2–H2O; initial rates at 1 min up to 500 turnovers min–1 at 0 °C in the epoxidation of cyclooctene are obtained.