Combination of Organometallic Catalysis with Organocatalysis

Toste published a paper in the current issue of Science. Utilizing the chiral phosphate anion as a couterion of metal with achiral ligand to induce chirality in organometallic catalysis. The structure of the phosphate anion they used was extensively studied in organocatalysis. The chiral BINOL based phophoric acid was first applied to the asymmetric Mannich type Reaction by Akiyama 1 2 and Terada 3 4 5. Then Magus Rueping( in Rueping's homepage there is also a similar paper which they say published on Angew. Chem. Int. Ed., but I cannot find it online) and Benjamin List used them in asymmetric imine reduction 6 7. Later they were employed by MacMillan and List to do the asymmetric reductive amination of ketone and DKR of alfa-branched aldehyde respectively 8 9. Recently, Rueping used this kind of catalysts to realize some amazing reduction. The BINOL based chiral phosphoric acid become a star molecule today in organocatalysis like Proline. Now their usage as a bridge between organocatalysis and organometallic catalysis will make them more popular.

Since I did organocatalysis as a Master student and am currently doing organometallic chemistry, when I begin my project here, one of my idea is to combine the organocatalysis with the organometallic catalysis, that is to use a achiral metal catalyst together with a chiral organocatalyst to do asymmetric reaction. That's very spotaneous based on my background and seems not novel at all. However, after the knowledge this paper, I think sometimes I should not undervalue my ideas.

Note: Reuping's paper could be found now titled "Dual Catalysis: A Combined Enantioselective Brønsted Acid and Metal-Catalyzed Reaction - Metal Catalysis with Chiral Counterions". In fact, Reuping's concept is different from the science paper. Though they said their reaction may involve a chiral counter ion catalyst, their reaction may most likely go through a mechanism in which the chiral phosphoric acid activate the imine substrate to provide stereo-control while the silver salt just act as an achiral catalyst to activate the alkyne.