Frank Lutz

Torsional isomerism of bent metallocene complexes. The structures of meso-and rac-bis(1-cyclohexyltetrahydroindenyl)zirconium dichloride in the solid state

Abstract Two molar equivalents of 1-cyclohexylindenyllithium were treated with ZrCl 4 (thf) 2 to give a ca . 1:1 mixture of meso - and rac -bis(1-cyclohexylindenyl)ZrCl 2 ( meso -/ rac - 4 ). Catalytic hydrogenation yielded a corresponding mixture of the bis(1-cyclohexyl-4,5,6,7-tetrahydroindenyl)ZrCl 2 diastereoisomers meso - 5 and rac - 5 . In both cases the diastereomers were separated by fractional crystallization. Complexes meso - and rac - 5 were characterized by an X-ray crystal structure study. In the crystal the molecular structure of complex rac - 5 is C 2 -symmetric, with the annulated six-membered ring systems arranged towards the open front side of the bent metallocene wedge and the cyclohexyl substituents oriented anti -periplanarly in the lateral sectors. In contrast complex meso - 5 has only one of the cyclohexyltetrahydroindenyl ligands arranged in this way, the cyclohexyl substituent of the other one pointing towards a central front position and the annulated six-membered ring being situated in the lateral position ( C 1 -symmetry).

SYSTEMATIC STRUCTURAL INVESTIGATIONS ON PHOSPHINES

This work contributes to the systematic investigation of phosphines. In an attempt to determine the nature, shape, volume and direction of the lone pairs at the phosphorus atoms in phosphines, high resolution X-ray structure analyses of triphenylphosphine, tris(p-methoxyphenyl) phosphine, bis(2,4,6-triisopropylphenyl)phosphine, 1,1 -bis(diphenylphosphino)ethene and 4,5,6-triphenyl-4-phosphaspiro[2.4]hept-5-en have been carried out. New valence force field param eters (TRIPOS force field) are presented which were developed on the basis of the molecular structures of the free phosphines. The results of crystal growing experiments using zone melting techniques are summarized.

Molecular Modelling: Ein Beitrag zum Verständnis der katalytischen enantioselektiven Hydrovinylierung von Styrol / Molecular Modelling: A Contribution to the Understanding of the Catalytic Enantioselective Hydrovinylation of Styrene

The hydrovinylation of styrene can be catalyzed by the addition of phosphane-modified Ni(II) compounds with high reactivity and enantioselectivity if the azaphospholene 1 is used as P-component of the catalysts. Until recently the industrial applications of 1 have been hampered by its difficult synthesis. To search for easier to synthesize, but equally well catalyzing derivatives of 1 a molecular modelling study was carried out. Based on already experimentally tested and structurally characterized azaphospholenes a model is developed, which not only leads to a better understanding of the catalytic process and but also to a relatively easy way to predict catalytic properties in these systems. Using an extended, customized valence force field several new derivatives of 1 have been tested. Their predicted and experimentally determined catalytic properties are in good agreement. The X-ray structures of the phenyl-substituted, monomeric azaphospholene 13, which hitherto results in the second best catalyst, and of its precursor 19 are presented.

Reactivity in Solid State and Electron Deformation Density Determinations

This contribution consists of three related topics. After some introductory remarks about the techniques used for Electron Deformation Density Determinations (EDD) the next part is concerned with the solid state photochemistry of styryl-α-pyrone and their isoelectronic nitrogen substituted isomorphs. Investigations of the EDD provide an explanation for the change in photoreactivity, since different forms of conjugation within the molecules as well as different π-π-interactions in the solid state are present.