The interaction of RR'N-PCl2 (1) with LiNR"SiMe3 gives monomeric phospha(IH)-azenes RR'N-P=N-R"; R = R"=i-C3H7, R'= (CH3)3C (3a); R=i-C3H7,R'=R" = (CH3)3C (3b); R = i-C3H7, R' = (CH3)3C, R"=(CH3)3Si (3c) as distillable liquids. 3a adds PCl3 with formation of RR'N-PCl-NR-PCl2, R = i-C3H7, R'=(CH3)3C (6).