Chiral calcium catalysts for asymmetric hydroamination/cyclisation
James S Wixey1, Benjamin D Ward
1School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, UK.
Chemical Communications (Cambridge, England)
|April 6, 2011
Summary
Chiral calcium complexes catalyze asymmetric hydroamination reactions. New catalysts achieve up to 26% enantioselectivity, a significant improvement for synthesizing chiral amines from amino-olefins.
Area of Science:
- Organometallic Chemistry
- Asymmetric Catalysis
- Synthetic Organic Chemistry
Background:
- Chiral 1,2-diamines are crucial ligands in asymmetric catalysis.
- Calcium complexes have shown promise as catalysts for hydroamination reactions.
- Developing efficient catalysts for asymmetric hydroamination is essential for synthesizing enantiomerically pure compounds.
Purpose of the Study:
- To investigate the efficacy of novel calcium complexes supported by chiral 1,2-diamines as catalysts for asymmetric hydroamination.
- To evaluate the impact of different substituents (R) on catalyst performance and enantioselectivity.
- To computationally study the structure of a representative calcium complex.
Main Methods:
- Synthesis of calcium complexes featuring chiral 1,2-diamine ligands.
- Asymmetric hydroamination reactions using amino-olefin substrates.
- Enantioselectivity determination using chiral chromatography or spectroscopy.
- Density functional theory (DFT) calculations for structural analysis.
Main Results:
- Calcium complexes with chiral 1,2-diamines demonstrated catalytic activity in asymmetric hydroamination.
- Enantioselectivities of up to 26% were achieved with specific catalyst structures ([Ca(NN(R)){N(SiMe(3))(2)}(THF)] where R = (t)Bu, (i)Pr, Ph, 4-C(6)H(4)F).
- This represents a significant enhancement in enantioselectivity compared to existing literature methods.
- DFT calculations provided insights into the structural properties of the [Ca(NN(Ph)){N(SiMe(3))(2)}(py)] complex.
Conclusions:
- Chiral calcium-diamine complexes are effective catalysts for asymmetric hydroamination.
- The developed catalysts offer improved enantioselectivity for the synthesis of chiral amines.
- Computational studies can aid in understanding the structure-activity relationships of these catalytic systems.
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