Showing papers by "Emmanuelle Schulz published in 2010"

Recoverable chiral salen complexes for asymmetric catalysis: recent progress

Abstract: Chiral salen-type complexes have already been proven to be particularly useful asymmetric catalysts for the preparation of a wide range of enantioenriched products. Research for efficient recovery and recycling of such complexes is ongoing and has already demonstrated the value of these procedures in terms of atom economy and overall economical savings. Results reported in the near past (2006–2009) dealing with the use of recyclable chiral salen complexes are summarized here, classified according to the type of heterogenization procedures involved.

Simple Chiral Diaminobinaphthyl Dilithium Salts for Intramolecular Catalytic Asymmetric Hydroamination of Amino‐1,3‐dienes

Abstract: Simple and easily accessible chiral lithium amide salts are reported as efficient (pre)catalysts for the diastereo- [up to (E:Z)=92:8] and enantioselective [up to 72% ee (E)] hydroamination/cyclisation of conjugated primary aminodienes. These chiral lithium salts are straightforwardly prepared by in situ combination of an N-substituted (R)-(+)-1,1′-binaphthyl-2,2′-diamine ligand and a commercial methyllithium solution. Information on the solid-state structure of these salts was obtained by X-ray analysis of a single crystal.

New Chiral Calixsalen Chromium Complexes: Recyclable Asymmetric Catalysts†

Abstract: A chiral N,N'-bis(salicylidene)ethylenediamine (salen) polymer has been prepared by a condensation reaction between a thiophenedisalicyladehyde derivative and (S,S)-cyclohexane-1,2-diamine. This polymeric compound was demonstrated to possess a cyclic structure with two to five repetitive units. The addition of chromium(II) salts led to the generation of a chiral catalyst that could be recovered as an insoluble powder. The performance of this new calixsalen-type catalyst was examined in various transformations, particularly in its ability to promote nucleophilic epoxide ring opening under heterogeneous conditions. The target products were obtained in high yields and with improved selectivity compared with those obtained by using analogous linear polymers. The arrangement of the catalytic sites in the cyclic structure is probably more suitable for the necessary cooperative bimetallic pathway of this demanding reaction. The catalyst could be successfully recycled. This approach represents the first use of calixsalen complexes under heterogeneous catalytic conditions.

“Diam-BINAP”; a Highly Efficient Monomer for the Synthesis of Heterogeneous Enantioselective Catalysts.

Abstract: The synthesis of a monomeric analogue of BINAP, diam-BINAP, is described. The polyaddition of this monomer with 2,6-diisocyanato toluene gave the corresponding oligomer, poly-NAP, with a polymerization degree of 8. The ruthenium complex of this polymer proved to be a very efficient heterogeneous catalyst for the hydrogenation of β-ketoesters (99% ee, 0.1 mol% of catalyst). Furthermore the catalyst could be easily reused four times by simple filtration without loss of activity or enantioselectivity.

Original Use of the Same Heterogeneous Chiral Catalyst Batch to Promote Different Asymmetric Reactions.

Abstract: An electrogenerated heterogeneous chiral (poly)salen-thiophene chromium complex successfully promoted different asymmetric catalytic reactions in an original successive manner, demonstrating its high stability and versatility.

Heterogeneous Catalytic Hydrogenation of Olefinic Substrates by poly-NAP.

Abstract: With our previously described poly-NAP, various olefinic substrates were reduced with selectivities comparable to those obtained by BINAP. For substrates which contained a methyl ester, the selectivities were higher than those observed for their carboxylic acid analogues.