Configurational Lability at Tetrahedral Phosphorus: syn/anti-Isomerization of a P-Stereogenic Phosphiranium Cation by Intramolecular Epimerization at Phosphorus
Ryan M. Tipker
6128 Burke Laboratory, Department of Chemistry, Dartmouth College, Hanover, NH, 03755 USA
Search for more papers by this authorDr. Jake A. Muldoon
6128 Burke Laboratory, Department of Chemistry, Dartmouth College, Hanover, NH, 03755 USA
Search for more papers by this authorDaniel H. Pham
6128 Burke Laboratory, Department of Chemistry, Dartmouth College, Hanover, NH, 03755 USA
Search for more papers by this authorDr. Balazs R. Varga
6128 Burke Laboratory, Department of Chemistry, Dartmouth College, Hanover, NH, 03755 USA
Search for more papers by this authorCorresponding Author
Prof. Russell P. Hughes
6128 Burke Laboratory, Department of Chemistry, Dartmouth College, Hanover, NH, 03755 USA
Search for more papers by this authorCorresponding Author
Prof. David S. Glueck
6128 Burke Laboratory, Department of Chemistry, Dartmouth College, Hanover, NH, 03755 USA
Search for more papers by this authorDr. Gary J. Balaich
Department of Chemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA, 92093 USA
Search for more papers by this authorProf. Arnold L. Rheingold
Department of Chemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA, 92093 USA
Search for more papers by this authorRyan M. Tipker
6128 Burke Laboratory, Department of Chemistry, Dartmouth College, Hanover, NH, 03755 USA
Search for more papers by this authorDr. Jake A. Muldoon
6128 Burke Laboratory, Department of Chemistry, Dartmouth College, Hanover, NH, 03755 USA
Search for more papers by this authorDaniel H. Pham
6128 Burke Laboratory, Department of Chemistry, Dartmouth College, Hanover, NH, 03755 USA
Search for more papers by this authorDr. Balazs R. Varga
6128 Burke Laboratory, Department of Chemistry, Dartmouth College, Hanover, NH, 03755 USA
Search for more papers by this authorCorresponding Author
Prof. Russell P. Hughes
6128 Burke Laboratory, Department of Chemistry, Dartmouth College, Hanover, NH, 03755 USA
Search for more papers by this authorCorresponding Author
Prof. David S. Glueck
6128 Burke Laboratory, Department of Chemistry, Dartmouth College, Hanover, NH, 03755 USA
Search for more papers by this authorDr. Gary J. Balaich
Department of Chemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA, 92093 USA
Search for more papers by this authorProf. Arnold L. Rheingold
Department of Chemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA, 92093 USA
Search for more papers by this authorAbstract
Tetrahedral main-group compounds are normally configurationally stable, but P-epimerization of the chiral phosphiranium cations syn- or anti-[Mes*P(Me)CH2CHPh][OTf] (Mes*=2,4,6-(t-Bu)3C6H2) occurred under mild conditions at 60 °C in CD2Cl2, resulting in isomerization to give a syn-enriched equilibrium mixture. Ion exchange with excess [NBu4][Δ-TRISPHAT] (Δ-TRISPHAT=Δ-P(o-C6Cl4O2)3) followed by chromatography on silica removed [NBu4][OTf] and gave mixtures of syn- and anti-[Mes*P(Me)CH2CHPh][Δ-TRISPHAT]⋅x[NBu4][Δ-TRISPHAT]. NMR spectroscopy showed that isomerization proceeded with epimerization at P and retention at C. DFT calculations are consistent with a mechanism involving P-C cleavage to yield a hyperconjugation-stabilized carbocation, pyramidal inversion promoted by σ-interaction of the P lone pair with the neighboring β-carbocation, and ring closure with inversion of configuration at P.
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