Phosphorus NMR Characterisation of P
N Bond Rotamers of a α-P₄S₃ Amide with a Conformationally Constrained Chiral Substituent

Bruce W. Tattershall, Julian G. Knight, Mark J. Andrews and Claire L. Booth, Z. Anorg. Allg. Chem., 2006, 632, 425.

Abstract:

Reactions of bicyclic α-P₄S₃I₂ with Hpthiq gave solutions containing α-P₄S₃(pthiq)I and α-P₄S₃(pthiq)₂, where Hpthiq is the conformationally constrained chiral secondary amine 1-phenyl-1,2,3,4-tetrahydroisoquinoline. The expected diastereomers have been characterised by complete analysis of their ³¹P{1H} NMR spectra. Hindered P-N bond rotation in the amide iodide α-P₄S₃(pthiq)I caused greater broadening of peaks in the room temperature spectrum of one diastereomer than in that of the other. At 183 K, spectra of two P-N bond rotamers for each diastereomer were observed and analysed. The minor rotamers showed strong evidence for steric crowding, having large diastereomeric differences in ¹J(P-P) and ²J(P-S-P) couplings (49 Hz, 16 % of value, and 4.4 Hz, 19 % of value, respectively).