(399c) Development of New Covalently Tethered Group 4 Metallocenes

Group 4 metallocenes bearing an ethylenebis(indenyl) (EBI) or an ethylenebis(tetra-hydroindenyl) (EBTHI) moiety are known to be very active and selective catalysts for reactions like hydrogenations, hydrosilylations and polymerizations. Although tremendous achievements have been made in the area of homogeneous chemical catalysis as well as in the implementation of these soluble complexes in industrial applications, such processes are not having as much impact on an industrial scale as may have been expected. The reasons may be that homogeneous catalysts lack the advantages of heterogeneous catalysts like easy separation and recycling of the catalysts, prevention of metal leaching, improvement of stability, etc. Within this project we present the development of heterogeneous Group 4 metallocenes which (i) are covalently bond to a solid support, such as H-terminated Si-surfaces or functional silica gel (ii) show high activity and selectivity for pharmaceutical GMP reactions (e.g., reduction of imines to chiral amines) and (iii) can be used to develop multifunctional catalysts, i.e., solid supports that feature two or more catalytic compounds. The development of these heterogeneous catalysts involves the preparation of functional ligands using a four step synthesis [1] in order to introduce tethers of various lengths and functionality to the metallocenes. The functional ligands and metallocenes are then immobilized on solid supports using different methods like UV-induced hydrosilylation [2] or chemical catalysis. State-of-the-art surface characterization methods are used in order to investigate the distribution and concentration of active sites on the surfaces. The development and optimization of the new metallocenes are accompanied with molecular modeling approaches using DFT methods (DFT = Density Functional Theory). Applying the B3LYP functional the relationship between function and structure of the catalysts as well as reaction profiles for the catalytic hydrosilylation of imines are studied [3]. The performance of the new heterogeneous metallocenes is compared to that of classic homogeneous catalysts, e.g., EBTHITibinol or EBTHITiCl2, which have proven to be potent catalysts for the hydrosilylation of imines leading to chiral amines with high yields and enantioselectivities.

[1] Panarello A. P., Vassylyev O., Khinast J. G., Synlett, 2005, 5, 797 [2] Langner A., Panarello A., Rivillon S., Vassylyev O., Khinast J. G., Chabal Y. J., J. Am. Chem Soc., 2005, 127, 12798 [3] Woelfler H., Flock M., Sassmannshausen J., Khinast J.G., manuscript in preparation