Nuclear magnetic resonance investigation of rotation about phosphorus(V)–nitrogen bonds in aminocyclodiphosph(V)azanes

Abstract

Hydrogen-1 n.m.r. data on the cyclodiphosph(V)azanes R₂N(X)[graphic omitted]Bu^t(R = Me, X = O, S, or Se; R = Et, X = S or Se) and Me₂N(O)[graphic omitted]R (R = Ph or CH₂Ph) indicate that rotation about the exo P^V–N bonds is slow on the n.m.r. time scale at ambient or sub-ambient temperatures. In the former series, trans isomers have higher rotational barriers, ΔG_Tc‡, than analogous cis isomers and these barriers are also greater for trans oxides than analogous sulphides or selenides. The rotational barriers for P^V–N and P^III–N have also been measured for the compounds Me₂N[graphic omitted] Bu^t(X = S, Se, or Mel), Me₂N(X)[graphic omitted]Bu^t(X = S, Y = lone pair; X = O, Y = O), and cis-Me₂N(S)[graphic omitted] Bu^t. Carbon-13 n.m.r. data obtained at various temperatures on geometrical isomers of Me₂N(X)[graphic omitted] Bu^t(X = O, S, or Se) indicate that J(PNC)(exo) is much more stereospecific than J(PNCH), especially when X = S or Se.