Gianluca Pozzi

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.

Metal Complexes of a Tetraazacyclotetradecane Bearing Highly Fluorinated Tails: New Catalysts for the Oxidation of Hydrocarbons under Fluorous Biphasic Conditions

Abstract The commercially available macrocycle tetraazacyclotetradecane (cyclam) has been converted into the fluorocarbon soluble ligand 1 by N-functionalization with RFCH2OCH2CH2OTs 3, wherein RF is a (per)fluorooxyalkylenic chain. Upon complexation with 1, transition metal salts can be selectively solubilized in fluorocarbons thus providing new catalysts for the oxidative functionalization of hydrocarbons under fluorous biphasic (FB) conditions.

PALLADIUM-CATALYZED HECK REACTION IN PERFLUORINATED SOLVENTS

Abstract Palladium-catalyzed coupling reaction of aryl iodides with methyl acrylate, commonly designated as the Heck reaction, can be performed in perfluorinated solvents, using perfluorocarbon-soluble triarylphosphines as ligands. The easy separation and recycling of the catalyst is also possible.

Hydrolytic kinetic resolution of terminal epoxides catalyzed by fluorous chiral Co(salen) complexes

Abstract Cobalt complexes of fluorous chiral salen ligands have been synthesized and tested as catalysts in the hydrolytic kinetic resolution of terminal epoxides. Whereas the activity of heavily fluorinated complexes was found to be rather low, a ‘light fluorous’ complex was shown to be an efficient and highly selective catalyst for this asymmetric ring-opening reaction. Several strategies for the isolation of reaction products and the recovery of the fluorous catalyst are also discussed.

Fluorous chiral ligands for novel catalytic systems

Abstract The relatively new fields of fluorous biphasic (FB) and supercritical catalysis, with their advantageous recycling properties, are quickly expanding to include examples of asymmetric catalysis. In order that catalysts are preferentially soluble in these media, various chiral ligands with perfluoroalkyl chains attached have been synthesised and studied. The use of these ligands, the effect of the perfluoroalkyl chains and reaction solvent on the activity and selectivity of the catalysts are herein discussed.

A convenient access to triarylphosphines with fluorous phase affinity

Abstract Perfluorocarbon-soluble triarylphosphines with electronic properties similar to those of tris( p -methoxyphenyl)phosphine can be easily prepared through O -alkylation of tris( p -hydroxyphenyl)phosphine oxide and subsequent reduction with trichlorosilane.

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.

Palladium(0)-catalyzed substitution of allylic substrates in perfluorinated solvents

Abstract Palladium(0)-catalyzed alkylation reactions of allylic substrates can be performed using the new concept of fluorous biphasic system, allowing a very easy recycling of the catalyst.

Asymmetric hydrogen transfer reduction of ketones using chiral perfluorinated diimines and diamines

Abstract Hydrogen transfer reduction of various ketones occurs in a mixture of perfluoroalkane/isopropanol using iridium complexes in association with chiral perfluorinated diimines or diamines as ligands. Enantioselectivity of up to 79% has been obtained. Recycling of the catalyst using chiral perfluorinated diamines as the ligands is possible with no loss of enantioselectivity and very low leaching of iridium in the organic phase.

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.