Conformational effects on PNCH, PNC, and PNSi spin coupling in tervalent phosphorus–nitrogen compounds

Abstract

The ¹H and ¹³C n.m.r. spectra of a series of tervalent phosphorus-nitrogen compounds having a known conformation about the P–N bond have been obtained. These measurements confirm previous assumptions that the coupling constants J(PNCH) and J(PNC) are relatively large and positive for a methyl group having a cis relation with the lone pair of electrons on phosphorus. J(PNCH) is small, and J(PNC) small and negative when the methyl group is trans to the lone pair. The results are discussed by reference to compounds of unknown conformation. The coupling constant, J(PNSi), in a series of silylaminophosphines, Ph₂P·NR·SiMe₃(R = Me, Et, Pr¹, or Bu^t), also appears to be related to the conformation adopted by the P–N bond.