In recent years, many articles describing the preparation of supported colloidal catalysts have been published. The semi‐hydrogenation of alkynes to yield cis‐alkenes is often used as a test reaction in these publications. Many highly selective catalysts are described. However, a satisfactory explanation for the high reported selectivity has never been shown. Here we report a study on the possible effects that lead to the large selectivity differences between current commercial Pd/C catalysts and our newly developed NanoSelect catalysts. The focus is on differences in chemical composition as well as catalyst characteristics. We use a focused ion beam scanning electron microscope (FIB‐SEM) to locate the metal particle with respect to the surface of the support. FIB‐SEM analysis clearly shows the absence of the active component inside the support material, which could explain the high observed selectivity. Nevertheless, an effect of the stabilizer cannot be ruled out.
Glycerol is an attractive renewable building block for the synthesis of polyglycerols, which find application in the cosmetic and pharmaceutical industries. The selective etherification of glycerol to higher oligomers was studied in the presence of CaO colloids and the data are compared with those obtained from NaOH and CaO. The materials were prepared by dispersing CaO, CaCO3, or Ca(OH)2 onto a carbon nanofiber (CNF) support. Colloidal nanoparticles were subsequently dispensed from the CNF into the reaction mixture to give CaO colloids that have a higher activity than equimolar amounts of bulk CaO and NaOH. Optimization of the reaction conditions allowed us to obtain a product with Gardner color number <2, containing no acrolein and minimal cyclic byproducts. The differences in the CaO colloids originating from CNF and bulk CaO were probed using light scattering and conductivity measurements. The results confirmed that the higher activity of the colloids originating from CaO/CNF was due to their more rapid formation and smaller size compared with colloids from bulk CaO. We thus have developed a practical method for the synthesis of polyglycerols containing low amounts of Ca.
We studied the surface modification of supported colloidal precious metal catalysts. Chiral compounds derived from cinchona alkaloids and prolinol were synthesized and used as stabilizers/reductants to yield Pd and Pt colloidal nanoparticles. The new Pd catalysts were found to be highly active and selective catalysts for the semihydrogenation of 3‐hexyn‐1‐ol to cis‐3‐hexen‐1‐ol. The stabilizers affected the activity of the catalyst but not the selectivity. The catalysts were also evaluated in the asymmetric hydrogenation of methyl pyruvate and isophorone. No enantioselectivity was observed, which indicated that surface modification by the stabilizer did not induce chirality in the substrate. Achiral supported Pd and Pt colloidal catalysts were modified with cinchonidine. The modified Pt catalysts demonstrated a high activity for the hydrogenation of methyl pyruvate and a modest enantioselectivity of 47 %, which indicated that the chiral induction of supported colloidal catalysts is possible by modifying the catalyst surface with a chiral reagent.
The synthesis of a number of novel 4,6-disubstituted tetrahydropyrimidinones is described. The synthetic route described is applied to the synthesis of two stereoisomers. The structure of one tetrahydropyrimidinone was determined by XRD and showed an interesting hydrogen-bonded ribbon in the direction of crystal growth. These pyrimidinones are members of a class of compounds with diverse bioactivity. An initial study of their activity versus HIV protease is included.
A B S T R A C TThe syntheses of three novel chiral 4,4 0 BOX ligands are described. The three ligands each have a chiral backbone and chiral sidearms, two of which are diastereomeric. These new ligands have been applied as copper complexes to asymmetric cyclopropanation reaction of styrene with ethyldiazoacetate. Enantioselectivities of up to 70% were obtained, which is the highest ee reported from the use of this ligand class in this reaction to date. The multiple stereogenic centres in the ligand resulted in a substantial additive effect and this is discussed along with interpretation of the results for previously described 4,4 0 BOX ligands, and a major computational study of the multiple reaction channels involved with ligands of this type. The use of complexes of 4,4 0 BOX ligands, as catalysts, in an allylic alkylation is also reported for the first time and ee's of >70% have been achieved in this reaction. These ligands were also applied to a Diels-Alder test reaction and again outperformed previous examples of this ligand type.
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