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NMR spectroscopic and computational study of static and dynamic E / Z isomerism in aminoiminophosphines R 2 N—P NMes *
Author(s) -
Gudat D.,
Hoffbauer W.,
Rozhenko A. B.,
Schoeller W. W.,
Povolotskii M. I.
Publication year - 2000
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/1097-458x(200010)38:10<861::aid-mrc748>3.0.co;2-z
Subject(s) - chemistry , isomerization , magic angle spinning , chemical shift , solid state nuclear magnetic resonance , solid state , double bond , nuclear magnetic resonance spectroscopy , computational chemistry , crystallography , stereochemistry , nuclear magnetic resonance , organic chemistry , catalysis , physics
The 31 P NMR spectra of the iminophosphines R 2 N—P NMes * [R = Me ( 2a ), Et ( 2b ), i‐Pr ( 2c ); Mes * = 2,4,6‐tri‐ tert ‐butylphenyl] were studied in the solid state under magic angle spinning conditions and in solution. Evaluation of the solid‐state data in connection with GIAO quantum chemical model calculations allows the characterization of the 31 P nuclear magnetic shielding tensors and leads to assignment of Z ‐configuration for the double bond in 2a and of the E ‐configuration for the double bonds in 2b and c . Comparison of the shifts δ iso with the chemical shift in solution (δ soln ) indicates that this configuration is retained in solution only for 2c , whereas solutions of 2a and b contain rapidly exchanging equilibrium mixtures of both E ‐ and Z ‐isomers. The analysis of the temperature dependence of δ soln allows for the first time the evaluation of Δ H and Δ S for this isomerization. The results reveal that in the case of 2b the configuration of the more stable stereoisomer is opposite to the conformation observed in the solid state. Copyright © 2000 John Wiley & Sons, Ltd.