Limited natural resources and an increasing demand for enantiomerically pure compounds render catalysis and especially heterogeneous asymmetric catalysis a key technology. The field has rapidly advanced from the initial use of chiral biopolymers, such as silk, as a support for metal catalysts to the modern research areas. Mesoporous supports, noncovalent immobilization, metal-organic catalysts, chiral modifiers: many areas are rapidly evolving. This Review shows that these catalysts have more to them than facile separation or recycling. Better activities and selectivities can be obtained than with the homogeneous catalyst and novel, efficient reaction mechanisms can be employed. Especially fascinating is the outlook for highly ordered metal-organic catalysts that might allow a rational design, synthesis, and the unequivocal structural characterization to give tailor-made catalysts.

Asymmetric heterogeneous catalysis.

Knapper werdende Rohstoffe und ein zunehmender Bedarf an enantiomerenreinen Verbindungen machen die Katalyse und insbesondere die heterogene asymmetrische Katalyse zu einer Schlusseltechnologie. Von den Anfangen, der Verwendung chiraler Biopolymere wie Seide als Trager fur Metallkatalysatoren, zu den modernen Forschungsfeldern hat sich das Gebiet rasant entwickelt. Mesoporose Trager, nichtkovalente Immobilisierung, metall-organische Katalysatoren, chirale Modifikatoren: viele Gebiete sind im Aufbruch. Dass hierbei von den Katalysatoren mehr geleistet wird, als nur leichte Abtrennung und Wiederverwendung zu ermoglichen, zeigt dieser Aufsatz. So konnen z. B. bessere Aktivitaten und Selektivitaten als bei der homogenen Katalyse und zudem neuartige, effiziente Reaktionsmechanismen erhalten werden. Besonders spektakular ist aber der Ausblick auf hochgeordnete metall-organische Katalysatoren, die “rational” entwickelt, synthetisiert und strukturell eindeutig charakterisiert werden konnen, um masgeschneiderte Katalysatoren zu erhalten.

Asymmetrische heterogene Katalyse

A series of guanidiniocarbonylpyridine receptors has been synthesized, and these compounds bind amino acids (carboxylate forms) in aqueous DMSO with association constants ranging from K = 30 to 460 M−1 as determined by NMR titration experiments. The differences in the complex stabilities can be correlated with steric and electrostatic effects with the aid of calculated complex structures. For example, the electrostatic repulsion between the pyridine nitrogen lone pair and the bound carboxylate makes anion binding less efficient than with the analogous pyrrole receptors previously introduced by us for carboxylate binding in water. Furthermore, steric interactions between the receptor side chain as in 2 b and the bound substrate also disfavor complexation.

Amino Acid Binding by 2‐(Guanidiniocarbonyl)pyridines in Aqueous Solvents: A Comparative Binding Study Correlating Complex Stability with Stereoelectronic Factors

Enantioselective Fluorescent Sensors for Chiral Carboxylates Based on Calix[4]arenes Bearing an L-Tryptophan Unit

Two novel types of chiral calix[4]arenes containing hydrazide and dansyl groups were synthesized and examined for their enantioselective recognition abilities by the fluorescence and 1 H NMR spectra in CHCl 3 . The results indicate that both 4a and 4b have excellent enantioselectivities to the N -protected alanine or phenylalanine anions.

Fluorescent sensors for amino acid anions based on calix[4]arenes bearing two dansyl groups

Novel homochiral molecular tweezers comprised of two chiral macrocyclic polyamine skeletons have been developed. These homochiral artificial receptors exhibit excellent chiral recognition ability toward the enantiomers of l - and d -amino acid derivatives (up to K L / K D =7.9, ΔΔ G 0 =−5.12 kJ mol −1 ) in CHCl 3 at 25.0°C.

Homochiral molecular tweezers as hosts for the highly enantioselective recognition of amino acid derivatives

Protected α-amino epoxides were successfully obtained in high threo-selectivity (up to 99%) under mild reaction conditions by using carbonyl 5,10,15,20-tetra(2,6-dichlorophenyl)porphyrin ruthenium(II) [Ru(TDCPP)CO] as catalyst and 2,6-dichloropyridine N-oxide (Cl2PyNO) as oxidant.

Highly diastereoselective epoxidation of protected α-amino alkenes catalyzed by ruthenium porphyrin/Cl2PyNO system

Manganese(III) 5,10,15-tris(tolyl)-20-(4-hydroxyphenyl) porphyrin covalently attached to Merrifield’s peptide resin (MPR) was prepared. The catalysts exhibit high reactivity and β-selectivity toward the epoxidation of cholest-5-ene derivatives with PhIO. Under mild reaction conditions, the catalyst was consecutively reused four times without detectable catalyst leaching and gave over 90% epoxide yield and over 99% β-selectivity.

Highly diastereoselective epoxidation of cholest-5-ene derivatives catalyzed by polymer-supported manganese(III) porphyrins

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Homochiral molecular tweezers as hosts for the highly enantioselective recognition of amino acid derivatives

Highly diastereoselective epoxidation of protected α-amino alkenes catalyzed by ruthenium porphyrin/Cl2PyNO system

Highly diastereoselective epoxidation of cholest-5-ene derivatives catalyzed by polymer-supported manganese(III) porphyrins