Nuclear magnetic resonance studies of rotation about phosphorus–nitrogen bonds in dialkylaminocyclodiphosphazanes
- 1 January 1977
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in J. Chem. Soc., Dalton Trans.
- No. 10,p. 1044-1048
- https://doi.org/10.1039/dt9770001044
Abstract
The 1H n.m.r. spectra of dimethylaminocyclodiphosphazanes, X[graphic omitted]R2[X = Cl, Y = NMe2, R1= Me, R2= But, R1= R2= But, R1= R2= Ph; X = Y = NMe2, R1= Me, R2= But, R1= R2= But, R1= R2= C6H4Z-p(Z = H, Cl, Me, and OMe)], at, or below, ambient temperatures show that in some cases the dimethylamino-protons are non-equivalent. Measurements of the free energy of activation (ΔG‡ Tc) in these, in the diethylamino-derivatives, (Et2N)[graphic omitted]R (R = But and Ph), and in the di-isopropylamino-derivative, Cl[graphic omitted]But, indicate that the non-equivalence is due to restricted rotation about the exocyclic phosphorus–nitrogen bonds. Exceptionally high barriers are found for one of the two possible isomeric forms of Cl[graphic omitted]But and of (Me2N)[graphic omitted]But(16.9 and 17.6 kcal mol–1 respectively), and there are substantial differences in ΔG‡ Tc(3–6 kcal mol–1) for pairs of geometrical isomers. The 31P chemical shifts of the aminocyclodiphosphazanes, measured by 1H-{3lP} double resonance, are temperature dependent, and this dependence is discussed in relation to possible conformational effects.Keywords
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