Stefan Bischoff

Water-soluble rhodium/phosphonate–phosphine catalysts for hydroformylation

Abstract We have developed new and efficient routes to modify phosphines with phosphonic acid groups. Phosphonate–phosphines showed high solubilities in water and were used to immobilise rhodium catalysts in the aqueous phase of biphasic systems. In the two-phase hydroformylation of propylene, some of the novel catalysts showed activities and regioselectivities similar to those of Rh/TPPTS. Amphiphilic Rh/phosphonate–phosphine catalysts were found widely superior to Rh/TPPTS in the hydroformylation of 1-octene.

Synthesis and Characterization of 4- and 4,4′-Phosphorylated2,2′-Bis(diphenylphosphanyl)-1,1′-binaphthyls

A convenient reaction sequence has been established to obtain selectively the mono- or bisphosphorylated BINAP derivatives 6−9. The structure of the new compounds was confirmed by NMR spectroscopy. The sodium salts of the phosphonic acid derivatives 8 and 9 can be used in aqueous biphasic catalysis.

Soluble and supported carbonylation catalysts derived from rhodium-phosphonate-phosphane complexes

Phosphonate-phosphanes form both chelate and open-chain complexes with rhodium, which can easily be converted into each other. This property has been used in the development of new and efficient carbonylation catalysts. During the catalytic cycle, the phosphane group is assumed to be coordinated to the transition metal, while the phosphoryl-oxygen of the phosphonate group is supposed to change between a free and a coordinated state, thus vacating or occupying a coordination site. IR studies support the hemilabile behaviour of surface Rh-complexes under the reaction conditions. Activation enthalpies, obtained for hemilabile rhodium catalysts in homogeneous methanol carbonylation, increased significantly with growing distance between phosphonate and phosphane group. Attempts of preparing stable rhodium complex catalysts adsorbed on silica or alumina for slurry-phase or vapour-phase carbonylations failed. Activated carbon has been shown to be a suitable support for hemilabile rhodium complexes, but normal diffusion of reactants begins to limit the carbonylation rate over the supported catalysts.

The role of promoter metals in the hydrocarbonylation of methanol over active carbon supported cobalt catalysts

Abstract The role of the promoter metals palladium and ruthenium in the mechanism of the hydrocarbonylation (reductive carbonylation) of methanol over cobalt/active carbon catalysts has been investigated. It has been found that the reduction steps on active Co sites are strongly affected by activated hydrogen transferred from promoter metal particles. Several indications for the existence and importance of hetero-bimetallic centers have been obtained by comparing activities and selectivities of mechanical mixtures of monometallic catalysts, of catalysts prepared by co-impregnation using different precursors and of mixed-metal cluster-derived catalysts. The close neighborhood of promoter metal and cobalt centers seems to be a precondition for the cooperative carbonylation and hydrogen activation, and spillover does not play an important role in the transfer of activated hydrogen. The role of the promoter metals may change with the loading. For example, ruthenium supported on active carbon showed a considerable hydrocarbonylation activity at low loadings.

Asymmetric hydroformylation and hydrogenation catalyzed by chiral rhodium and ruthenium complexes of phosphorylated 2,2′-bis(diphenyl-phosphino)-1,1′-binaphthyls

Abstract In situ-generated rhodium complexes of mono- and bisphosphorylated enantiopure BINAP ligands have been used for the asymmetric hydroformylation of styrene and vinylacetate. Corresponding Ru-complexes have been investigated in the homogeneous and biphasic asymmetric hydrogenation of dimethyl itaconate. An increase in the enantioselectivity of about 6–9% compared to BINAP was observed in the vinylacetate hydroformylation. For the aqueous biphasic hydroformylation of styrene the most enantioselective rhodium diphosphine catalyst (27% e.e.) up to now has been found.

Control of the specific surface area of silica by a sol–gel process using 2-methylpentane-2,4-diol

An improved method for the preparation of porous silica xerogels is described. Tetraethoxysilane (TEOS) as the starting alkoxide is modified by transesterification with 2-methylpentane-2,4-diol (MPD) prior to hydrolysis. The specific surface area and the pore size distribution of the calcined gels can be easily controlled by variation of the preparation parameters. Thus, a xerogel exhibiting a specific surface area of 1108 m2 g–1 was obtained after calcination at 450 °C for 4 h. The species formed by the transesterification of tetramethoxysilane (TMOS) with MPD were studied by 29Si NMR spectroscopy and chemical ionisation mass spectroscopy (CI MS).

Supported phosphonate-phosphane complexes for vapour-phase carbonylation

Abstract Supported mixed bidentate rhodium and iridium complexes derived from phosphonate-phosphanes were studied in the methanol carbonylation and in the hydroformylations of ethylene and propylene. Heterobidentate complexes of rhodium showed higher activities than rhodium bisphosphane complexes in homogeneous and vapour-phase methanol carbonylation. The hemilabile behaviour of the mixed bidentate complexes may explain these findings. In ethylene hydroformylation, supported phosphonate-phosphane Rh-complexes did not show higher activities than supported rhodium-bisphosphane complexes. However, phosphonate-phosphane ligands suppressed the undesired ethane formation in this reaction. Excellent rhodium catalysts for vapour-phase carbonylations were obtained, when Rh phosphane complexes were anchored in lamellar zirconium phosphonate structures with mixed phosphonate anions. These catalysts were several times more active than rhodium supported on silica or on activated carbon, showed a superior stability, and produced butyraldehydes with up to 98% chemoselectivity in the vapour-phase hydroformylation of propylene.

Immobilization of rhodium catalysts in biphasic systems and in layered structures using phosphonated phosphines

Uncomplicated syntheses of phosphines substituted with phosphonic acid groups have been developed. The ligands were used to immobilize rhodium catalysts in aqueous biphasic systems and between the layers of zirconium phosphate hybrid materials. Effective immobilization, high activities (turnover frequencies higher than 600 h-1) and selectivities were found in the hydroformylation of 1-octene to nonanal and 2-methyloctanal.

Indication of water in the coordination sphere of rhodium by conversions of 2,5-dimethoxy-2,5-dihydrofuran with syngas

Abstract 2,5-Dimethoxy-2,5-dihydrofuran did not form the expected aldehydes when water-soluble rhodium-catalysts were used for the conversion with syngas. Instead of hydroformylation, hydrogenation was the main reaction path in water, where 2,5-dimethoxytetrahydrofuran and its hydrolysis product, succinic dialdehyde, were obtained. The formation of hydrogenation products indicates water in the coordination sphere of rhodium. This may provide us with information on the environment of an active metal in aggregated structures like micelles and vesicles which are gaining in importance in biphasic catalysis.

PHOSPHINE- AND PHOSPHITE-SUBSTITUTED 3,3′-BI-INDOLIZINES- NEW ATROPISOMERIC LIGANDS

Abstract For the first time enantiomerically pure phosphine- or phosphite-substituted 1,1′-alkyl-3,3′-bi-indolizines were obtained. In situ prepared rhodium complexes of these compounds were tested in hydroformylation of styrene and methylstyrene.