Aqueous Phase Transfer Hydrogenation of Aryl Ketones Catalysed by Achiral Ruthenium(II) and Rhodium(III) Complexes and their Papain Conjugates
Several ruthenium and rhodium complexes including 2,2′‐dipyridylamine ligands substituted at the central N atom by an alkyl chain terminated by a maleimide functional group were tested along with a newly synthesized Rh(III) complex of unsubstituted 2,2′‐dipyridylamine as catalysts in the transfer hydrogenation of aryl ketones in neat water with formate as hydrogen donor. All of them except one led to the secondary alcohol products with conversion rates depending on the metal complex. Site‐specific anchoring of the N‐maleimide complexes to the single free cysteine residue of the cysteine endoproteinase papain endowed this protein with transfer hydrogenase properties towards 2,2,2‐trifluoroacetophenone. Quantitative conversions were reached with the Rh‐based biocatalysts, while modest enantioselectivities were obtained in certain reactional conditions.
Design of Artificial MetalloenzymesReview
Homogeneous and enzymatic catalysis offer complementary means to generate enantiomerically pure compounds. For this reason, in a biomimetic spirit, efforts are currently under way in different groups to design artificial enzymes. Two complementary strategies are possible to incorporate active organometallic catalyst precursors into a protein environment. The first strategy utilizes covalent anchoring of the organometallic complexes into the protein environment. The second strategy relies on the use of non‐covalent incorporation of the organometallic precursor into the protein. In this review, attention is focused on the use of semisynthetic enzymes to produce efficient enantioselective hybrid catalysts for a given reaction. This article also includes our recent research results and implications in developing the biotin–avidin technology to localize the biotinylated organometallic catalyst precursor within a well‐defined protein environment.