Chiral diamine-silver(I)-alkene complexes: A quantum chemical and NMR study

The ability of chiral diamine silver complexes to bind chiral and prochiral alkenes has been analyzed in detail. The stereoselectivity in binding of alkenes to a chiral ethanediamine silver complex has been investigated by NMR. The low-energy conformations of several small model complexes have been explored by DFT methods. By successive substitution of the computational model complexes, it has been possible to elucidate the role of each amine substituent in achieving successful discrimination of alkenes. The conformational space has been fully explored using small model systems, allowing an unbiased calculation of stereoselectivities that match well the experimental results. For a chiral allylic alcohol substrate, the correct stereoselectivity was obtained only when the structures were optimized with a continuum representation of the solvent. The discrepancy between gas phase and solution data is found to result from a competition between internal stabilization and solvation of the OH group of the substrate

Molecular mechanics predictions and experimental testing of asymmetric palladium-catalyzed allylation reactions using new chiral phenanthroline ligands

Molecular mechanics calculations were used to probe the conformational properties of a number of substituted phenanthrolines and their eta(3)-allylpalladium complexes. Special attention was focused on phenanthrolines bearing chiral, terpene-derived, alkyl and alkenyl groups at C(2). Based upon these calculations, predictions could then be made regarding the suitability of the several ligands for use in asymmetric palladium-catalyzed substitution reactions of allylic acetates. Each of the substituted phenanthrolines was prepared by straightforward means. Use of these ligands in catalytic allylations gave results which were in good agreement with the calculation-based predictions. The highest levels of asymmetric induction were predicted and were obtained with a readily available 2-(2-bornyl)phenanthroline ligand 13. The results were compared with previously reported data obtained using other ligands. Overall, this work provides further indication of the potential utility of a combined calculational/experimental approach for the design of chiral catalysts