H. Patin

Biphasic liquid-liquid hydrogenation catalysis by aqueous colloidal suspensions of rhodium: The choice of the protective-colloid agent and the role of interfacial phenomena

Microheterogeneous catalytic systems using aqueous suspensions of rhodium particles are proved to be efficient for alkene hydrogenation in biphasic liquid-liquid medium provided that the method of stabilization and the interfacial phenomena are properly chosen and controlled. Aqueous supensions stabilized by specially designed trianionic molecules or by hydrophilic polymer (PVA) have been studied. A series of trisulfonated molecules 1 with modulated solution behaviors (surfactant or hydrotrope) depending on the nature of the substituents has been used to stabilize aqueous suspensions of oxidized (polar) or reduced (non polar) rhodium particles. Stabilization of polar particles occurs whatever the substituents when stabilization of metallic apolar particles requires surfactants bearing a significant lipophilic part. In the former case, highly stable suspensions of rhodium nanoparticles with controlled size are obtained in micellar solutions. Both oxidized and reduced rhodium suspensions efficiently catalyzed octene hydrogenation in liquid-liquid medium and it is established that high activity and possible recovery and recycling of the catalyst can be achieved by the control of interfacial parameter e.g. the interfacial tension. In the same way, common polymer-protected colloidal suspensions of Rh(0) particles are proved to efficiently catalyze hydrogenation in two liquid phases systems provided that optimized amounts of surfactants are added to reduce the interfacial tension without emulsification. From these results a relationship between interfacial tension and catalytic activity in biphasic system is proposed.

Oxidation of alkanes with hydrogen peroxide catalysed by iron salts or iron oxide colloids in reverse microemulsions

Abstract Catalytic oxidation of alkanes occurs in reverse (water in oil) microemulsions stabilized by an anionic surfactant (Aerosol OT®). The catalytically active microemulsion is generated by mixing two reverse microemulsions containing respectively an aqueous solution of iron (FeII or FeIII) and an aqueous solution of H2O2 (30%) dispersed in liquid alkanes (continuous oil phase). This microemulsion system is active in the CH bond oxidation of various liquid alkanes (cycloalkanes, decalin, tetralin, alkylbenzenes) into ketones and secondary and tertiary alcohols at room temperature. The selective oxidation of secondary carbons into ketones and tertiary carbons into alcohols is interpreted by the intervention of iron(V) oxene intermediates rather than radical Fenton-type mechanisms. Polynuclear aggregates such as colloidal hydrous ferric oxides generated by hydrolysis within the aqueous microdroplets are assumed to be the catalytically active species. In fact, we demonstrate that previously prepared iron oxide colloids (Fe2O3 and FeOOH) similarly catalyze the oxidation of alkanes with hydrogen peroxide in reverse microemulsions. The low interfacial water—hydrocarbon tension and the very high interfacial area in liquid—liquid dispersions greatly favour the catalytic process.

Structure of a carbenic precursor of tetrathiafulvalene coordinated to a triiron octacarbonyl cluster complex

Abstract The reaction between 1,3-dithiole 2-thione and Fe2(CO)9 gives a 1,3-dithiole-2-ylidenetriiron octacarbonyl cluster complex, (C3H2S2)Fe3(CO)8S2 the structure of which has been determined by X-ray diffraction.

Importance of counter-ion nature in aryl sulfonated ligands: An improvement in two-phase catalysis

Carbon-carbon coupling of myrcene with methyl acetylacetate in two-phase system using various water-soluble rhodium(I) complexes was studied. The influence of the sulfonate counter-ion nature in TPPTS and in 1,4-bis(diphenylphosphino)butane meta-tetra sulfonated was investigated.

Iron carbonyl complexes of cithiocarbonates. X-ray crystal structure of Fe4(CO)12S(SCH2C5H4FeC5H5)(SCH3)

Abstract Reaction of S-ferrocenylmethyl-S-methyldithiocarbonate (I) with diiron nonacarbonyl gives the dissymmetrically bridged complex (μ-SCH 2 C 5 H 4 FeC 5 H 5 )-(μ-SCH 3 )Fe 2 (CO) 6 , as a mixture of syn and anti isomers, along with the title compound, the structure of which has been determined by X-ray diffraction. This latter complex consists of two Fe 2 (CO) 6 units bridged by two S-alkyl ligands and by a central sulfur atom; its structure is compared with those of related molecules.