Structures in solution of organophosphorus-lithium compounds

Abstract

Low temperature ³¹P and ⁷Li nmr spectra of Et₂O solutions of lithiated organophosphorus compounds have resolved coupling constants ¹J(³¹P-⁷Li) in the range 30–50 Hz. These spectra demonstrate the covalent nature of the species and also provide information regarding the state of molecular association. Ph₂PLi] is found to be a symmetrical dimer whilst PhMePLi] gives a mixture of dimer and trimer. PhHPLi] exists in only one form, detailed consideration of the ³¹P and ⁷Li results suggesting a trimeric structure. (PH₂P)₂CHLi and Ph₂P]Ph₂P(S)]CHLi are found to be covalent monomers. it is proposed that in the dimers and trimers phosphorus retains an electron lone pair and that the bonding is of the multi-centre electron deficient type as found in the organolithuims themselves.