An Ab initio Study of the P−C Bond Rotation in Phosphoryl- and Thiophosphoryl-Stabilized Carbanions: Five- and Six-Membered Heterocycles

• DOI: 10.1021/jo9602783
• Publication Date: 2002-07-26T05:02:57Z
• Authors: Michael Kranz; Scott E. Denmark; Kevin A. Swiss; Scott R. Wilson
• Keywords: Carbanion; Isodesmic reaction; Conformational isomerism; Dilithium; Lone pair

The potential energy surfaces for the P−C bond rotation in 2-oxo- and 2-thioxo-2-methyl-1,3,2-diazaphosphorinane -1,3,2-diazaphospholidine anions have been investigated at MP4(SDQ)/6-31+G*//HF/6-31+G* + ZPE. Four stationary points found six-membered ring species. lowest structures exhibit a completely or nearly planar carbanion with its substituents parallel to PX axis (X = O, S). transition state (TS) strongly pyramidalized which lone pair (LP) is approximately perpendicular bond. Isodesmic equations, length comparisons, orbital interactions indicate superior ground (GS) stabilization of thioxo derivative favorable TS oxo Both effects cooperate furnish computationally experimentally observed higher (ca. 2.5 kcal/mol both cases) rotational barrier 2-thioxo-1,3,2-diazaphosphorinane based anions. Coordination lithium cation chalcogen atom yields distinct preference axial/equatorial orientation nitrogen species diequatorial arrangement analog, perfect agreement X-ray crystallographic data. crystal structure lithio 2-(1-methylethyl)-1,3-dimethyl-1,3,2-diazaphosphorinane 2-sulfide·3THF reported it consistent existing theoretical experimental geometries. five-membered analogs (1,3,2-diazaphospholidines) same conformational GS TS. activation derivatives as well. Whereas only one substituent changes diazaphosphorinanes during coordinate, backbone responds diazaphospholidines.