Despite its industrial importance metal-catalyzed hydroformylation has not found much application in organic synthesis. This may be primarily due to the difficulty in controlling selectivity issues in the course of this interesting carbon-carbon bond forming reaction. In the last decade a number of excellent solutions to these problems have been devised. Thus, frontiers of chemo-, regio-, diastereo-and enantioselectivity control in the course of the hydroformylation and their application in organic synthesis are the major focus of this review. Mechanistic and conceptual background have been included where appropriate. Additionally, recent progress in the field of domino reactions employing the hydroformylation as a key step is covered.
A new concept for the construction of bidentate ligands for homogeneous metal complex catalysis is described. The concept relies on the self-assembly of monodentate ligands through hydrogen bonding. As a prototype of such systems, 6-diphenylphosphanyl-2-pyridone (6-DPPon) was shown to form a chelate in the coordination sphere of a transition metal center through unusual pyridone/hydroxypyridine hydrogen bonding (X-ray). This hydrogen bonding stays intact in a catalytic reaction as proven upon highly regioselective hydroformylation of terminal alkenes. Regioselectivities and reactivities observed rank the 6-DPPon/rhodium system among the most active and regioselective catalysts for n-selective hydroformylation of terminal alkenes.
The odd couple: Inspired by the principle of DNA base pairing a conceptually new approach for the generation of a heterobidentate‐ligand library based on self‐assembly through hydrogen‐bonding is realized. From a 4×4 library a catalyst that shows outstanding activity and excellent regioselectivity could be identified (see scheme; FGR=functional group, Do=donor group).
The first chiral ligand library based on self-assembly through complementary hydrogen-bonding was realized. From a 10 x 4 ligand library, catalysts that show excellent activity and enantioselectivity for the asymmetric rhodium-catalyzed hydrogenation have been identified.
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