CHIRAL Rh/SiO2 CATALYSTS FOR ENANTIOSELECTIVE HYDROGENATION REACTIONS: THE ROLE OF (S,S)-DIPAMP AS CHIRAL MODIFIER AND STABILIZER ON METALLIC NANOPARTICLES SYNTHESIS

Abstract

Rhodium nanoparticles were successfully stabilized by the (S,S)-1,2-ethanediylbis [(2-ethoxyphenyl)phenylphosphine] ((S,S)-DIPAMP) deposited on SiO 2 prepared by a facile reduction and impregnation method. The chiral catalysts obtained were efficient for the enantioselective hydrogenation reactions of prochiral compounds. The catalysts synthesized from [Rh(μ-OMe)(COD)] 2 in the presence of different amounts of a ligand used as chiral stabilizer, showed good metal dispersion. As shown by TEM, the metal particle size ranged between 1 and 2 nm using stabilizer and 9.1 nm was achieved without chiral ligand. Other techniques were used to characterize the chiral catalysts such as X-ray diffraction (XRD), electron diffraction, thermogravimetric analysis (TGA) and N 2 adsorption-desorption isotherms.(S,S)-DIPAMP was used as the stabilizer of metal particles to prevent growing and agglomeration, and it also acts as chiral modifier inducing enantioselectivity in the asymmetric hydrogenation of 3,4-hexanodione (HD), ethyl pyruvate (EP), ketopantolactone (KP), and acetophenone (AP). Under specific conditions such as 25 °C, 40 bar of H 2 and substrate/Rh=100, 1%Rh-(S,S)-DIPAMP/SiO 2 chiral catalysts showed excellent catalytic performance with conversion and enantiomeric excess (ee) levels up to 99% and 54% respectively.

Functional Colloidal Stabilization

“…[145] The presence of the phosphonate group in the surfmer also allowed crystallization of hydroxylapatite on the particle surface. [146] Also cysteine can be used as a stabilizer in the preparation of CdTe nanocrystals (Table 11, entry 3). Using the chiral stabilizer aggregation of the metal nanoparticles was prevented.…”

“…The generated chiral metal oxide nanoparticles were applied for enantioselective hydrogenation of prochiral compounds. [146] Also cysteine can be used as a stabilizer in the preparation of CdTe nanocrystals (Table 11, entry 3). [147] Achiral acetylene monomers were polymerized in chiral micelles by helix-sense-selective polymerization to generate optically active helical polymer emulsions.…”

Immobilized chiral rhodium nanoparticles stabilized by chiral P-ligands as efficient catalysts for the enantioselective hydrogenation of 1-phenyl-1,2-propanedione

“…In this field, chiral modification of metal surfaces has expanded successfully along the years [17][18][19]. A variety of experimental techniques provides chiral materials [20,21] including supported asymmetric homogeneous catalysts [20], chiral modifiers with heterogeneous supported metal catalysts [22][23][24][25][26][27][28][29][30], colloidal metal particles stabilized with chiral ligands [18,19,31,32,33], grafted chiral modifiers on supports [34,35,36], functionalized polymers [37] and chiral nanoparticles immobilized on metal oxide surfaces [20]. Typically SiO2, Al2O3 or TiO2 are the most used supports for this kind of heterogenization [20,36,38].…”

P-Stereogenic Phosphines for the Stabilisation of Metal Nanoparticles. A Surface State Study

“…The enantioselective catalysis on surfaces is commonly explained by three main mechanisms: the presence of chiral crystalline atomic structures at the surface, chiral adsorbates which modify the surface and chiral modifiers which control the approach of the substrate on the surface [11,12]. The stereoselective reactions mainly concern hydrogenations and C-C bond formation reactions based on the third mechanism [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]. In this context, the optically pure ligand should be able to generate both a strong enough coordination at the metallic surface to stabilize MNPs and an asymmetric environment to efficiently lead to one of the expected stereoisomers during the organic transformation.…”

“…Ligands coordinate at the metallic surface by different ways, such as dative donor bonds between heteroatoms of the ligands and the metal surface, and also by π-interactions through aromatic fragments of the ligands and the nanoparticle. The nature of the chiral stabilisers reported in the synthesis of MNPs is wide-ranging, including dienes [15], cinchona alkaloids [16][17][18], mono or bidentate amines [19][20][21], phosphorus-based ligands (phosphites [22][23][24][25][26], diphosphines [27][28][29][30], secondary phosphine oxide [31]). P-stereogenic phosphines are well-known in catalysis using organometallic complexes as catalytic precursors, finding applications in hydrogenation, transfer hydrogenation, cyclopropanation, hydrovinylation, Diels Alder reactions and allylic substitutions [32][33][34].…”