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

Hydrogen-1 n.m.r. data on the cyclodiphosph(V)azanes [R2N(X)PNBut]2 (R = Me, X = O, S, or Se; R = Et, X = S or Se) and [Me2N(O)PNR]2 (R = Ph or CH2Ph) indicate that rotation about the exo PV–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, ΔGTc‡, than analogous cis isomers and these barriers are also greater for trans oxides than analogous sulphides or selenides. The rotational barriers for PV–N and PIII–N have also been measured for the compounds Me2NP[NBut]2P(X)NMe2 (X = S, Se, or MeI), Me2N(X)P[NBut]2P(Y)Cl (X = S, Y = lone pair; X = O, Y = O), and cis-Me2N(S)P[NBut]2P(Se)NMe2. Carbon-13 n.m.r. data obtained at various temperatures on geometrical isomers of [Me2N(X)PNBut]2 (X = O, S, or Se) indicate that J(PNC) (exo) is much more stereospecific than J(PNCH), especially when X = S or Se