Carmen Claver

Rhodium catalyzed hydroformylation

Preface. 1. Introduction to hydroformylation P.W.N.M. van Leeuwen. 2. Hydroformylation with unmodified rhodium catalysts R. Lazzaroni, et al. 3. Rhodium phosphite catalysts P.C.J. Kamer, et al. 4. Phosphines as ligands P.W.N.M. van Leeuwen, et al. 5. Asymmetric hydroformylation C. Claver, P.W.N.M. van Leeuwen. 6. Hydroformylation in organic synthesis S. Castillon, E. Fernandez. 7. Aqueous biphasic hydroformylation J. Herwig, R. Fischer. 8. Process aspects of rhodium-catalyzed hydroformylation P. Arnoldy. 9. Catalyst preparation and decomposition P.W.N.M. van Leeuwen. 10. Novel developments in hydroformylation J.N.H. Reek, et al. Subject index.

Synthesis of 2-substituted-benzothiazoles by palladium-catalyzed intramolecular cyclization of o-bromophenylthioureas and o-bromophenylthioamides

Abstract 2-Amino-, and 2-alkyl-benzothiazoles have been efficiently prepared by palladium catalyzed cyclization of o -bromophenylthioureas and o -bromophenylthiamides. Results were best with the Pd 2 (dba) 3 /monophosphine catalytic system.

Chiral diphosphites derived from D-glucose: new ligands for the asymmetric catalytic hydroformylation of vinyl arenes.

A series of novel diphosphite ligands derived from readily available D-(+)-glucose has been synthesized. These ligands have been applied to the Rh-catalyzed hydroformylation of vinyl arenes. Both excellent enantioselectivities (up to 91%) and regioselectivities (up to 98.8%) were achieved under mild conditions. The advantage of these ligands is that their modular natures allow facile, systematic variation in the configurations at the stereocenters [C(3), C(5)] at the ligand bridge and in the biphenyl substituents, enabling their effects on the stereoselectivity to be studied. Results show that the absolute configuration of the product is governed by the configuration at the stereogenic center C(3), while the level of the enantioselectivity is influenced by a cooperative effect between stereocenters C(3) and C(5). Replacement of the tert-butyl substituent by methoxy substituents at the para positions of the biphenyl moieties improved the enantioselectivities. We have characterized the rhodium complexes formed under CO/H2 by NMR techniques and in situ IR spectroscopy and have observed that there is a relationship between the structure of the [HRh(CO)2(PP)] species and their enantiodiscriminating performance in hydroformylation. Enantioselectivities were highest with ligands with a strong bis-equatorial coordination preference, while an equilibrium of species with bis-equatorial and equatorial-axial coordination modes considerably reduced the ees.

Hydroxycarbonylation of styrene with palladium catalysts The influence of the mono- and bidentate phosphorus ligand.

Abstract A systematic study of the hydroxycarbonylation reaction of styrene is described. The effect of the catalytic precursor and the reaction conditions on the results of the reaction was investigated. Several monophosphines (PPh 3 , P(p-Tol) 3 , P(p-C 6 H 4 OMe) 3 , P(p-C 6 H 4 F) 3 , PPh 2 (o-Tol), PMe 3 , PCy 3 ) and diphosphines (dppe, dppp, dppb, dppf, HomoXantphos, DPEphos, Xantphos, BDPP, BINAP, BPPFA, DIOP) were applied to control the regioselectivity of the reaction. The effect of the bite angle of the diphosphines has also been studied. Catalysts containing monophosphines as ligands give 2-phenylpropanoic acid as the major product and the 3-phenyl propanoic acid is obtained when diphosphines are used. Two catalytic cycles are proposed to explain the influence of the different palladium precursors with mono- and diphosphines.

On the Mechanism of the Hydroxycarbonylation of Styrene with Palladium Systems

We present a review concerning the mechanism involved in the hydroxycarbonylation of styrene. We discuss the intermediates proposed in the literature, the effect of the acidic medium, the reactivity and kinetics, as well as the results of theoretical calculations on hydroxycarbonylation and related reactions. We have performed an in situ high-pressure NMR study to obtain more insight into the mechanisms that control the regioselectivity and have assessed how this is affected by the phosphorus ligand and the catalyst precursor. We observed palladium hydride and palladium acyl species and we suggest a catalytic cycle involving palladium hydride, palladium alkyl, and palladium acyl intermediates.

Preparation of a new clay-immobilized highly stable palladium catalyst and its efficient recyclability in the Heck reaction

The immobilization of a series of bis-carbene-pincer complexes of palladium(II) on montmorillonite K-10 affords the preparation of effective catalysts for the C–C coupling in a standard Heck reaction. The supported catalysts so obtained, show catalytic activity similar to their homogeneous counterparts. The determination of Pd content on the supported catalysts by XPS and elemental analysis, before and after each catalytic reaction, shows that leaching is negligible. Once the reaction conditions were optimized, we were able to recycle the catalyst at least ten times, without significant loss of activity.

Tunable furanoside diphosphite ligands. A powerful approach in asymmetric catalysis

A series of highly tunable furanoside diphosphite ligands, derived from readily available D-(+)-xylose and D-(+)-glucose, are discussed. Their modular nature allows a facile systematic variation in the configuration of the stereocentres at the ligand bridge and in the biaryl substituents. This enabled to select a ligand for each particular reaction that provided enantioselectivities that are comparable to those of the best catalysts previously reported in different asymmetric reactions.

Asymmetric hydroformylation of styrene catalyzed by carbohydrate diphosphite-Rh(I) complexes

A series of new chelating diphosphite ligands with a furanoside backbone and axially chiral biphenyl or binaphthyl moieties have been synthesized. Their Rh(I) complexes have been tested as catalyst precursors for the asymmetric hydroformylation of styrene. Systematic variation in chirality at both chiral sugar backbone stereocenters (C-3 and C-5) and either the axial chiral biphenyl or binaphthyl substituents revealed a remarkable effect on the selectivity of the hydroformylation catalysts. In this way, by judicious choice of these elements, both regio- and enantioselectivities can be optimized. Thus, both high enantioselectivity (up to 93% S) and regioselectivity in 2-phenylpropanal (up to 98.8%) were found under mild reaction conditions (15–40°C, 10 bar of syngas) for the ligand with a glucofuranoside backbone and bis(trimethylsilyl)-2,2′-biphenyl moiety. The solution structures of HRh(L–L)(CO)2 complexes have been studied by high pressure NMR and IR. Varying the configuration of the binaphthyl moieties revealed a remarkable effect on the diphosphite coordination modes on the intermediate HRh(L–L)(CO)2 species and, therefore, on enantioselectivity. Enantioselectivity was highest for ligands with a strong bis-equatorial coordination preference.

A new and efficient catalytic method for synthesizing isocyanates from carbamates

Abstract Operationally simple, recyclable and environmentally friendly montmorillonite efficiently catalyses dealcoholysis of a wide range of mono- and dicarbamates to isocyanates.

First successful application of diphosphite ligands in the asymmetric hydroformylation of dihydrofurans

Good enantioselectivities and excellent regioselectivities are achieved in the Rh-catalyzed asymmetric hydroformylation of 2,5- and 2,3-dihydrofuran using diphosphite ligands; whereby the backbone of the ligand is crucial to suppressing isomerization and obtaining high ees.