Ab initio investigation of the diels-alder reaction between 2H-phosphole and phosphaethene: A model for phosphole dimerization

Abstract

All four possible Diels‐Alder reactions between 2H‐phosphole and phosphaethene were examined at various theoretical levels, including HF, MP4SDQ, CCSD(T), and CASSCF. MP2/6‐31G* 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 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 MP4SDQ/6‐31G*//HF/6‐31G* these reactions are exothermic by 34–38 kcal mol−1 and have very low activation energies, 5–7 kcal mol−1. The PP/CC regioisomer products are lower in energy than the CP 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 CP endo product. Larger basis sets, electron correlation, and solvent favor the transition state leading to the experimentally observed PP/CP endo isomer. The dimerization of phosphole is, therefore, kinetically controlled. Based on geometric and electron density analysis, the reactions are concerted and synchronous. © 1997 by John Wiley & Sons, Inc.

Asymmetric Diels–Alder reaction with >C=P– functionality of the 2-phosphaindolizine-η1-P-aluminium(O-menthoxy) dichloride complex: experimental and theoretical results

“…Ab initio investigations of the DA reaction of phosphaethene with 2 H -phosphole [49] and with 1,3-butadiene [50–52] revealed low activation energies and a preference for the endo approach. In the present case, endo attack of the 1,3-butadiene molecule from the sterically more hindered Re face expectedly involves the higher-energy transition structure TS3 .…”

Diels−Alder Reaction of Phosphaethene with 1,3-Dienes: An ab Initio Study

“…The DA cycloadditions of phospha-1,3-butadienes with ethene were computed to be very exothermic with low activation energies . Ab initio investigations of the [2 + 4] cycloadditions of phosphaethene with 2 H -phosphole and with 1,3-butadiene − revealed such low activation energies and a preference for endo approach. It was concluded that the presence of phosphorus in a DA reactant lowers the activation energy relative to that of the hydrocarbon systems, due to the weakness of the CP π bond compared to the CC π bond .…”

Electronic and Molecular Structures of Polyheteroles: II. Aromaticity and Quinoidicity

“…Considerable attention has been paid to these polymers because of their good conductivities and environmental stability with respect to oxidation. Polypyrrole and polythiophene are typical examples but the recent advances in organic chemistry enable us to synthesize novel heteroles 3,4) by the replacement of the heteroatom X with boron (B; borole), 5,6) silicon (Si; silole), 7) oxygen (O; furan), 8) tellurium (Te; tellurophene), 9) selenium (Se; selenophene), 10) or phosphorous (P; phosphole) 11) and then to expand the types of polyheteroles. 12) Characteristic features in these novel heteroles are a deficiency or an excess of a electron: 13) A single electron is deficient when the heteroatom is replaced by a group III or IV element, while an excess of a electron results when the heteroatom is replaced by a V or VI element (Fig.…”