Papers by Chretien Simons
Dalton Transactions, 2013
This article describes a new strategy for the recycling of a homogeneous hydroformylation catalys... more This article describes a new strategy for the recycling of a homogeneous hydroformylation catalyst, by selective adsorption of the catalyst to tailor-made supports after a batchwise reaction. The separation of the catalyst from the product mixture is based on selective non-covalent supramolecular interactions between a ligand and the support. Changing the solvent releases the active catalyst back into the reactor and allows a subsequent batch reaction with the recycled active catalyst. For this purpose, the bidentate NixantPhos ligand has been equipped with a pyridine group. The corresponding rhodium pre-catalyst [Rh(Nix-py)(acac)] (acac = acetylacetonate) forms a very selective, active and highly stable catalyst, and able to reach a turnover number (TON) of 170 000 in a single run (reaction performed in nearly neat 1-octene, S/C ratio of 200 000, at 140°C, 20 bars syngas pressure). Various commercially available supports have been explored in binding studies and recycling experiments. The end-capped silica-alumina performs the best so far with respect to ligand-adsorbing properties for the current purpose. Although this system has not been fully optimized, four recycling runs could be performed successfully. † This contribution is dedicated to Professor David J. Cole-Hamilton on the occasion of his 65th birthday. ‡ Electronic Supplementary Information (ESI) available: Ligand synthesis, experimental details and additional NMR spectra. See
Samenvatting Dankwoord Curriculum Vitae small modifications of the ligand, the reaction could be ... more Samenvatting Dankwoord Curriculum Vitae small modifications of the ligand, the reaction could be fine-tuned to give the desired enantioselectivity. The continuation of Knowles' search for better catalysts, perfectly demonstrates the difficulty of predicting the influence of ligand alterations. Dimerisation of PAMP, led to the second commercially applied ligand, DiPAMP. With this molecule 2-acetamidocinnamic acid could be reduced with an ee of 95%, an increase of 27 Figure 3. a) The final step in the total synthesis of laulimalide (1), demonstrating the potential of the Ti-catalysed Sharpless asymmetric epoxidation ((+)-DITP= (+)-(R,R)-diisopropyl tartrate). b) Isomerization of 1 to isolaulimalide (3), which can occur during deprotection. This competing side reaction is avoided, since the total synthesis using SEA eliminates the deprotection step.
Chemical Communications, 2004
Rhodium-MonoPhos was successfully immobilised by ionic interactions on aluminosilicate AlTUD-1. T... more Rhodium-MonoPhos was successfully immobilised by ionic interactions on aluminosilicate AlTUD-1. The resulting new heterogeneous catalyst can be used in water and showed excellent enantioselectivity and activity in the asymmetric hydrogenation of methyl-2-acetamidoacrylate.
Topics in Catalysis, Nov 1, 2006
The combination of immobilised Rh-MonoPhos (5-AlTUD-1) and Acylase I afforded a chemo-enzymatic o... more The combination of immobilised Rh-MonoPhos (5-AlTUD-1) and Acylase I afforded a chemo-enzymatic one-pot process for the enantioselective synthesis of amino acids in water, without the need for isolation of intermediates. In addition, the enzymatic hydrolysis increases the enantiopurity of the product from 95% ee to >98% ee. Compatibility studies revealed that compartmentalisation of the catalysts is essential to achieve high yields and optical purities.
Journal of Molecular Catalysis B-enzymatic, Aug 1, 2008
To investigate the full potential of hydrolases for the removal of two amine-protecting groups, 1... more To investigate the full potential of hydrolases for the removal of two amine-protecting groups, 15 different, commercially available lipases, acylases, proteases and esterases were studied for the hydrolyses of N-acetyl and N-formyl protecting groups. In addition to the well-known acylases from porcine kidney and Aspergillus melleus, this screening revealed that porcine liver esterase and the lipases from Rhizomucor miehei and Pseudomonas stutzeri are also catalysts for the hydrolysis of N-acetylalanine. The activity of lipases in this reaction was unexpected, since lipases are commonly believed not to hydrolyse amides. In addition, from these 15 enzymes, three were found to be active in the hydrolysis of N-formylalanine, i.e. porcine liver esterase and the two acylases. This is the first example where esterase is employed to deprotect N-formyl amides.
Advanced Synthesis & Catalysis, May 1, 2006
The combination of immobilised Rh-Mono-Phos (1-AlTUD-1) and acylase I afforded a chemoenzymatic, ... more The combination of immobilised Rh-Mono-Phos (1-AlTUD-1) and acylase I afforded a chemoenzymatic, one-pot process for the enantioselective synthesis of amino acids in water, without the need for isolation of intermediates. In addition, the enzymatic hydrolysis increases the enantiopurity of the product from 95% ee to > 98% ee. Compatibility studies revealed that for optimum results compartmentalisation of the catalysts is required.
Chemistry: A European Journal, Nov 19, 2004
A new Brønsted acidic aluminosilicate, AlTUD-1, with ideal characteristics for catalyst immobilis... more A new Brønsted acidic aluminosilicate, AlTUD-1, with ideal characteristics for catalyst immobilisation (mesoporous structure, high surface area, and high Al(tetrahedral)/Si ratio), was used successfully for the noncovalent anchoring of two well-established asymmetric hydrogenation catalysts: [Rh(I)(cod)[(R,R)-MeDuPHOS]]BF4 (1) and [Rh(I)(cod)[(S,S)-DiPAMP]]BF4 (2). The new heterogeneous catalysts, 1-AlTUD-1 and 2-AlTUD-1, prepared by a straightforward ion-exchange procedure, were highly active and selective in the asymmetric reduction of dimethyl itaconate (3) and methyl 2-acetamidoacrylate (4), giving enantiomeric excesses of up to >98%. The catalysts showed similar behaviour to their homogeneous counterparts. Catalyst 2-AlTUD-1 could be re-used multiple times without loss of enantioselectivity or activity. Leaching of Rh showed a significant dependence on the polarity of the solvent in which the catalysis was performed. By applying tert-butylmethyl ether (MTBE) as solvent, the loss of Rh could be reduced to <0.1%. The solvent also had a noteworthy effect on the enantioselectivity in the hydrogenation of 4 (an effect not seen with 3 as substrate), that is, in MeOH the ee was 92%, in MTBE it dropped to 26% when using 2-AlTUD-1 as catalyst.
Topics in Catalysis, 2006
The combination of immobilised Rh-MonoPhos (5-AlTUD-1) and Acylase I afforded a chemo-enzymatic o... more The combination of immobilised Rh-MonoPhos (5-AlTUD-1) and Acylase I afforded a chemo-enzymatic one-pot process for the enantioselective synthesis of amino acids in water, without the need for isolation of intermediates. In addition, the enzymatic hydrolysis increases the enantiopurity of the product from 95% ee to >98% ee. Compatibility studies revealed that compartmentalisation of the catalysts is essential to achieve high yields and optical purities.
Journal of Molecular Catalysis B: Enzymatic, 2008
To investigate the full potential of hydrolases for the removal of two amine-protecting groups, 1... more To investigate the full potential of hydrolases for the removal of two amine-protecting groups, 15 different, commercially available lipases, acylases, proteases and esterases were studied for the hydrolyses of N-acetyl and N-formyl protecting groups. In addition to the well-known acylases from porcine kidney and Aspergillus melleus, this screening revealed that porcine liver esterase and the lipases from Rhizomucor miehei and Pseudomonas stutzeri are also catalysts for the hydrolysis of N-acetylalanine. The activity of lipases in this reaction was unexpected, since lipases are commonly believed not to hydrolyse amides. In addition, from these 15 enzymes, three were found to be active in the hydrolysis of N-formylalanine, i.e. porcine liver esterase and the two acylases. This is the first example where esterase is employed to deprotect N-formyl amides.
Journal of Catalysis, 2006
To determine the influence of the support on the asymmetric hydrogenation of dehydroamino acids u... more To determine the influence of the support on the asymmetric hydrogenation of dehydroamino acids using noncovalently immobilised catalysts, Rhodium-MonoPhos was successfully immobilised on four different anionic carrier materials: a mesoporous aluminosilicate (AlTUD-1), phosphotungstic acid on alumina (PWTUD), Nafion, and a Nafion silica composite (SAC-13). These supported catalysts were evaluated in the asymmetric reduction of methyl-2-acetamidoacrylate. Although most of the catalysts were highly selective, the activity and the loss of rhodium were strongly dependent on the type of support. PWTUD appeared to be the best support for this application, because it gave the catalyst with the highest activity and virtually no leaching in any solvent. Its superior anchoring ability derives from the additional bonding between the Rh and the phosphotungstic acid. Nafion, on the other hand, was by far the poorest support, giving very low activity. Immobilisation with this support relies on encapsulation rather than on ionic interactions. Its encapsulating properties not only prevent the complex from going into solution, but also prevent the substrate from reaching the catalytic site.
Chemistry - A European Journal, 2004
A new Brønsted acidic aluminosilicate, AlTUD-1, with ideal characteristics for catalyst immobilis... more A new Brønsted acidic aluminosilicate, AlTUD-1, with ideal characteristics for catalyst immobilisation (mesoporous structure, high surface area, and high Al(tetrahedral)/Si ratio), was used successfully for the noncovalent anchoring of two well-established asymmetric hydrogenation catalysts: [Rh(I)(cod)[(R,R)-MeDuPHOS]]BF4 (1) and [Rh(I)(cod)[(S,S)-DiPAMP]]BF4 (2). The new heterogeneous catalysts, 1-AlTUD-1 and 2-AlTUD-1, prepared by a straightforward ion-exchange procedure, were highly active and selective in the asymmetric reduction of dimethyl itaconate (3) and methyl 2-acetamidoacrylate (4), giving enantiomeric excesses of up to >98%. The catalysts showed similar behaviour to their homogeneous counterparts. Catalyst 2-AlTUD-1 could be re-used multiple times without loss of enantioselectivity or activity. Leaching of Rh showed a significant dependence on the polarity of the solvent in which the catalysis was performed. By applying tert-butylmethyl ether (MTBE) as solvent, the loss of Rh could be reduced to <0.1%. The solvent also had a noteworthy effect on the enantioselectivity in the hydrogenation of 4 (an effect not seen with 3 as substrate), that is, in MeOH the ee was 92%, in MTBE it dropped to 26% when using 2-AlTUD-1 as catalyst.
Advanced Synthesis & Catalysis, 2006
The combination of immobilised Rh‐MonoPhos (1‐AlTUD‐1) and acylase I afforded a chemo‐enzymatic, ... more The combination of immobilised Rh‐MonoPhos (1‐AlTUD‐1) and acylase I afforded a chemo‐enzymatic, one‐pot process for the enantioselective synthesis of amino acids in water, without the need for isolation of intermediates. In addition, the enzymatic hydrolysis increases the enantiopurity of the product from 95% ee to >98% ee. Compatibility studies revealed that for optimum results compartmentalisation of the catalysts is required.
European Polymer Journal, 2001
The oxidative polymerisations of 2,6-dimethylphenol with copper-(1-methylimidazole) complexes as ... more The oxidative polymerisations of 2,6-dimethylphenol with copper-(1-methylimidazole) complexes as the catalyst precursor compounds in dierent solvents showed the catalysts to be extremely active when using acetonitrile. Acetonitrile can act as a labile ligand for copper and also prevent the catalyst to become poisoned due to hydrolysis. Addition of increasing amounts of water leads to a progressive deactivation of the catalyst.
Applied Catalysis A: General, 2001
Poly(2,6-dimethyl-1,4-phenylene ether) (PPE) [J. Polym. Sci. A 36 (1998) 505], which is widely us... more Poly(2,6-dimethyl-1,4-phenylene ether) (PPE) [J. Polym. Sci. A 36 (1998) 505], which is widely used in high-performance engineering plastics, is obtained by the copper-catalyzed oxidative coupling of 2,6-dimethylphenol. The oxidative polymerizations have been carried out in acetonitrile with copper-imidazole complexes as the catalyst precursor compounds, which appeared to be extremely active. Different substituents on the imidazole ring showed that both the ligand basicity and the steric hindrance close to the coordinated nitrogen atom are important factors to increase the catalytic activity. Higher activities are always found with an excess of ligand and when using monodentate ligands instead of didentate ones. Most likely, the imidazole moieties may also act as base. Another nitrogen donor ligand, viz. 2-methyl-oxazoline, has been successfully tested, showing a very good activity in this oxidative coupling reaction.
Uploads
Papers by Chretien Simons