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Chiral Diamine−Silver(I)−Alkene Complexes:  A Quantum Chemical and NMR Study

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posted on 18.07.2005, 00:00 by Elsa Kieken, Olaf Wiest, Paul Helquist, Maria E. Cucciolito, Germana Flores, Aldo Vitagliano, Per-Ola Norrby
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.

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