A simple and efficient method for the preparation of N-phosphonio formamidine derivatives of the general formula [R”2N−C(H)=N−P(R’)R2]+X− is described. The data recorded in solution and the single crystal X-ray studies revealed that these compounds are best described by the combination of the two mesomeric N-phosphonio formamidine [R”2N−C(H)=N−P(R’)R2]+ and iminium phosphazene [R”2N=C(H)−N=P(R’)R2]+ forms. Formamidine phosphorus ylides i Pr2N−C(H)=N−P(CH2)R2 were prepared after addition of t BuLi at –78°C from the corresponding N-phosphonio compounds. [(PhCN)2Pd(Cl)2] was reacted with i Pr2N−C(H)=N−P(CH2) i Pr2 to form the dimeric complex [( i Pr2N−C(H)=N−P(CH2) i Pr2)Pd(Cl)(μ-Cl)]2 which was structurally characterized by X-ray analysis. The deprotonation reactions conducted on [ i Pr2N−C(H)=N−PPh3]+X− occurred via an intramolecular rearrangement to give the cyanamide compound i Pr2N−C≡N and PPh3; transient formation of the amino-phosphazene-carbene i Pr2N−C−N=PPh3 was not observed.