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Assignment of Phosphorus NMR Parameters to Absolute Configurations in Chiral Phosphorus Sulfide Cage Compounds, using Ab Initio Methods
Author(s) -
Tattershall Bruce W.
Publication year - 2005
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.200500016
Subject(s) - chemistry , diastereomer , chemical shift , conformational isomerism , ab initio , phosphorus , computational chemistry , crystallography , ab initio quantum chemistry methods , molecule , isotropy , stereochemistry , organic chemistry , physics , quantum mechanics
Abstract The closo cage molecules α‐ and β ‐P 4 S 3 ( μ ‐NCH(Me)Ph) were modelled at the RHF/3‐21G* and MPW1PW91/DZVP levels. For each, the conformational space corresponding to rotation about the C–N bond was explored, and relative average electronic energies were calculated. The β ‐isomer was more stable than the α‐isomer by 10.7 kJ mol −1 , according to the DFT calculations, in contrast to the unsubstituted model compounds α‐ and β ‐P 4 S 3 ( μ ‐NH), where the α‐isomer was more stable. GIAO calculations of phosphorus isotropic NMR shieldings, in the rotamers, led to relative average chemical shifts in the diastereomers. Comparison with experimental chemical shift differences gave an assignment to absolute configuration for α‐P 4 S 3 ( μ ‐NCH(Me)Ph), which agreed with the assignment obtained by comparing calculated relative diastereomer stability with observations. For β ‐P 4 S 3 ( μ ‐NCH(Me)Ph), the GIAO calculations allowed relative assignment of observed chemical shifts to the nitrogen bridgehead phosphorus atoms.