Ab initio investigation of the diels-alder reaction between 2H-phosphole and phosphaethene: A model for phosphole dimerization
✍ Scribed by Salzner, Ulrike; Bachrach, Steven M.; Mulhearn, Debbie C.
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 415 KB
- Volume
- 18
- Category
- Article
- ISSN
- 0192-8651
No coin nor oath required. For personal study only.
✦ Synopsis
All four possible Diels᎐Alder reactions between 2 H-phosphole and phosphaethene were examined at various theoretical levels, including HF, Ž . MP4SDQ, CCSD T , and CASSCF. MP2r6-31G* geometry optimizations could not be employed since the potential energy surface is qualitatively incorrect at this level of theory, due to the inherent underestimation of the activation Ž . energies ameliorated at higher-order MP or coupled-cluster levels . Solvent effects were examined employing the Onsager, polarized continuum, and isodensity and surface polarized continuum models. At MP4SDQr6-31G*rrHFr6-31G* these reactions are exothermic by 34᎐38 kcal mol y1 and have very low activation energies, 5᎐7 kcal mol y1 . The PᎏPrCᎏC regioisomer products are lower in energy than the CᎏP isomers and, within each pair, the exo isomer is lower in energy. At low computational levels the smallest activation energy is for the reaction leading to the CᎏP endo product. Larger basis sets, electron correlation, and solvent favor the transition state leading to the experimentally observed PᎏPrCᎏP endo isomer. The dimerization of phosphole is, therefore, kinetically controlled. Based on geometric and electron density analysis, the reactions are concerted and synchronous.