Bispidine derivatives as molecular tools for studies of (-Allyl)palladium complexes : Ligand synthesis and analythical cpplications

Sammanfattning: Determination of structural and stereochemical features of reaction intermediates in transition metal catalysed reactions is of central interest. Bispidine derivatives as ligands in (π-allyl)palladium complexes in combination with 1H NMR spectroscopy are shown to be useful tools for revealing structural characteristics of these reaction intermediates. As a support for the conclusions drawn from NMR investigations, X-ray crystallography and calculated structures were used.Complexes of bispidine derivatives with varying substitution pattern and different pre-formed bis[(η3-allyl)palladium chloride] complexes were formed. The resulting complexes were analysed with 1H NMR spectroscopy, especially regarding the inter-ligand NOEs and the chemical shift effects due to anisotropic effects. It is shown that a large steric interaction between the aromatic systems of N,N'-diphenylated bispidine derivatives and various (π-allyl)palladium systems can be obtained. This steric interaction can be used for hindering rotation around C-C single bonds in (π-allyl)palladium ligands.Furthermore, the nearness of the aromatic systems and the (π-allyl)palladium ligand give rise to anisotropic effects that, after quantification, can give information about the structure in such complexes. The inter-ligand NOEs can, in the case of a N,N-diphenyl substituted bispidine derivative, be used for assignment of relative configuration in a set of acyclic (π-allyl)palladium ligands. With a bispidine derivative carrying chiral substituents, the inter-ligand NOEs were used for assignment of absolute configuration of (π-allyl)palladium ligands.