LDA-mediated orthometalations: Structural and mechanistic studies on substrate independent reaction rates

ORGN 268

Kanwaljit Singh, ks259@cornell.edu and David B. Collum. Department of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, NY 14853-1301
Rate studies on orthometalation of arenes mediated by LDA/THF indicate mechanisms based on LDA monomers. Since 6Li and 15N NMR spectroscopies demonstrate that LDA exists as a dimer in THF solutions, deaggregation must occur prior to arene orthometalation. The dimer-monomer equilibrium is fully maintained during a rate-limiting orthometalation. Kinetic investigations at low temperature using fast-reacting arenes suggest a shift in the rate-determining step from orthometalation to deaggregation. Fast trapping of the LDA monomers reveals the influence of mixed aggregates generated during the course of the reaction. Models treating the complex equilibria in LDA-based metalations will be discussed.

 

Metal-Mediated Reactions and Syntheses
1:00 PM-5:00 PM, Monday, 29 August 2005 Washington DC Convention Center -- 202B, Oral

Division of Organic Chemistry

The 230th ACS National Meeting, in Washington, DC, Aug 28-Sept 1, 2005