ABSTRACT
A bifunctional imidazolium linker was used for the production of highly crosslinked element organic frameworks by Suzuki-coupling with tetrafunctional boronic acids. The resulting porous materials are good heterogeneous organocatalysts in the N-heterocyclic carbene-catalyzed conjugated umpolung of α,ß-unsaturated cinnamaldehyde.
Subject(s)
Acrolein/analogs & derivatives , Boronic Acids/chemistry , Heterocyclic Compounds/chemistry , Imidazoles/chemical synthesis , Methane/analogs & derivatives , Acrolein/chemistry , Catalysis , Heterocyclic Compounds/chemical synthesis , Imidazoles/chemistry , Methane/chemistry , Molecular Structure , Particle Size , Porosity , Stereoisomerism , Surface PropertiesABSTRACT
Chiral metal-organic frameworks with a three-dimensional network structure and wide-open pores (>30 Å) were obtained by using chiral trifunctional linkers and multinuclear zinc clusters. The linkers, H(3) ChirBTB-n, consist of a 4,4',4''-benzene-1,3,5-triyltribenzoate (BTB) backbone decorated with chiral oxazolidinone substituents. The size and polarity of these substituents determines the network topology formed under solvothermal synthesis conditions. The resulting chiral MOFs adsorb even large molecules from solution. Moreover, they are highly active Lewis acid catalysts in the Mukaiyama aldol reaction. Due to their chiral functionalization, they show significant levels of enantioselectivity, thereby proving the validity of the modular design concept employed.
ABSTRACT
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.
