P-stereogene, polydentate Phosphorodiamidite und deren Anwendung in der asymmetrischen Katalyse
- P-stereogenic, polydentate phosphorodiamidites and their application in asymmetric catalysis
Barwinski, Bernhard; Leitner, Walter (Thesis advisor); Klankermayer, Jürgen (Thesis advisor)
Dissertation / PhD Thesis
Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020
This thesis deals with the synthesis of P-stereogenic phosphine-phosphorodiamidite-ligands based on chiral amino alcohols as well as their application in the synthesis of rhodium(I)-complexes and in asymmetric catalysis.In the first part, the synthesis of tridentate diphosphine-phosphorodiamidite ligands on the basis of Betti bases was envisaged. These BettiPhos ligands provide a stereogenic phosphorus as characteristic element. The introduction of a phosphine group into the Betti-Base backbone via the amine and the aldehyde building block was investigated first. Moreover, tridentate BettiPhos ligands were synthesized and isolated based on bis(diphenylphosphinophenyl)amines via a multi-step synthesis. The ligands were analyzed regarding their stereochemistry and the isomerization kinetics of the stereogenic phosphorus was investigated via VT-NMR spectroscopy to generate a general understanding concerning the stereochemistry of these compounds. The new ligands were tested in their complexation of rhodium(I) and [Rh(nbd)(PPP)]BF4 complexes were isolated. The complexes were characterized using XRD analysis and the absolute configuration around the stereogenic phosphorus was confirmed via their crystal structure. These complexes showed a distorted trigonal-bipyramidal or a distorted square-planar geometry, respectively, containing a facial coordinating P,P,P-ligand. Moreover, the conversion of the tridentate BettiPhos-ligands with [Rh(cod)Cl]2 led to a P N bond cleavage in the ligand backbone including a chloride-transfer from [Rh(cod)Cl]2 to the phosphorodiamidite group. Additionally, the bis(diphenylphosphinophenyl)amine fragment was coordinating to rhodium in the manner of a PNP-pincer ligand. One of these obtained [Rh(PNP)(P*)] type complexes could be crystallized showing a distorted square-planar structure. In the second part of this thesis, P-stereogenic, bidentate Phosphine-Phosphorodiamidite ligands were synthesized based on ephedrine, a naturally abundant chiral amino alcohol. These bidentate ligands could be obtained via condensation of ephedrine with PCl3 and a chiral phosphine amine. One ligand was successfully crystallized and the absolute configuration of the stereogenic phosphorus was confirmed via XRD analysis. The ligands were converted to the corresponding cationic [Rh(cod)(PP)]+ complexes using [Rh(acac)(cod)]BF4 or [Rh(cod)Cl]2 precursors and then applied in asymmetric catalysis. In rhodium-catalyzed asymmetric hydroformylation of styrene and vinyl acetate only low enantioselectivity of about 15% ee could be achieved. In rhodium-catalyzed asymmetric hydrogenation of dimethyl itaconate and methyl-2-acetamido acrylate good enantioselectivities of up to 95% ee could finally be reached.