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Published June 30, 2004 | Supplemental Material
Journal Article Open

A Computational Model Relating Structure and Reactivity in Enantioselective Oxidations of Secondary Alcohols by (−)-Sparteine−Pd^(II) Complexes


The key interactions responsible for the unique reactivity of (−)-sparteine−PdX_2 complexes (X = chloride, acetate) in the enantioselective oxidation of secondary alcohols have been elucidated using quantum mechanics (B3LYP DFT with the PBF polarizable continuum solvent model). From examining many possible pathways, we find the mechanism involves:  (1) substitution of the alcohol in place of an X-group, (2) deprotonation of the bound alcohol by the deposed anion and free sparteine, (3) β-hydride elimination through a four-coordinate transition state in which the second anion is displaced but tightly associated, (4) replacement of the ketone product with the associated anion. The enantioselectivities observed under base-rich reaction conditions follow directly from calculated energies of diastereomeric β-hydride elimination transition states incorporating (R) and (S) substrates. This relationship reveals an important role of the anion, namely to communicate the steric interaction of the ligand on one side of the PdII square plane and the substrate on the other side. When no anion is included, no enantioselectivity is predicted. Locating these transition states in different solvents shows that higher dielectrics stabilize the charge separation between the anion and metal and draw the anion farther into solution. Thus, the solvent influences the barrier height (rate) and selectivity of the oxidation.

Additional Information

© 2004 American Chemical Society. Received 23 December 2003. Published online 4 June 2004. Published in print 1 June 2004. We thank Eric Ferreira, Jeffrey Bagdanoff, Raissa Trend, Julius Su, and Jonas Oxgaard for helpful discussions. J.M.K. thanks the National Science Foundation for financial support. This research was partly funded by the NSF (CTS-01322002), ChevronTexaco, and the NIH-NIGMS (R01 GM65961-01), and the facilities used were funded by grants from ARO-DURIP, ONR- DURIP, IBM-SUR, and the Beckman Institute. All calculations were performed with Jaguar 4.0 and Jaguar 5.0.35

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