Synthetic routes to mono-N-functionalized P2N2-ligands

Three different synthetic routes have been explored for the synthesis of the mono-N-substituted phosphinoamine N-ethyl,N?bis[2(diphenylphosphino)phenyl]propane-1,3-diamine: (a) selective alkylation of N,N?bis[2(diphenylphosphino)phenyl]propane-1,3-diamine; (b) linkage of the different fragments of N-ethyl,N?bis[2(diphenylphosphino)phenyl]propane-1,3-diamine; (c) selective acylation of N,N?bis[2(diphenylphosphino)phenyl]propane-1,3-diamine followed by acetyl reduction. While approaches (a) and (b) were unsuccessful, N-ethyl,N?bis[2(diphenylphosphino)phenyl]propane-1,3-diamine was obtained by route (c) via separation of the mono- and di-alkylated P2N2-species obtained from reduction, through complexation of Ni(NO3)26H2O followed by demetallation reaction with KCN. Additional related phosphinoamine chelates and phosphonium adducts were synthesized and characterized by conventional physico-chemical techniques.