Novel Mono Coordinating Phosphorus Ligands for Homogenous Catalysis

New classes of chiral auxiliaries will be synthesized and tested as ligands in transition metal catalyzed carbon- carbon bond forming reactions. Molecules with certain symmetry properties are called chiral and can exist in two forms which behave like image and mirror image. Species with this relationship are called enantiomers showing identical physical and chemical properties with the only exception that they behave differently when reacting with either enantiomer of another molecule. Since all organisms are built up from molecular building blocks consisting of only one of the enantiomeric forms this has several dramatic consequences. An important practical one is the different response of an organism to different enantiomers of antibiotics; only one form exhibits the desired beneficial effect, the opposite enantiomer is either inactive or even harmful. As a consequence efficient methods for the enantioselective production of bioactive compounds are highly desirable. A high level of enantioselectivity ("asymmetric induction") was often observed with transition metal catalyzed reactions proceeding under the influence of chiral ligands as auxiliaries. This so called "asymmetric catalysis" is also very attractive from the view point of economy since only the desired enantiomer is produced using a minimum amount of precious catalyst. However, the question of tailor-made catalysts with high stereoselectivity and high reactivity but with low substrate specifity is still open. The aim of the project is to design new classes of chiral phosphine and phosphite ligands which can be easily modified to tune their steric and electronic properties. The target structures consist of either C3- or (pseudo) C2- symmetrical units, where a phosphorus(III) atom is placed within a "chiral pocket", allowing the desired highly stereoselective interaction with the substrate. New ligands will be applied for a variety of enantioselective carbon- carbon bond forming reactions. To optimize the results, structures of most promising ligands will be modified based on experimental and theoretical investigations.