Skeletally stabilized di- and triphosphazane formation and stereoselection from reactions of phosphadiazoles C6H4(NH)2PPh (7), C6H4(NH)2P(S)Ph (8), C6H4(NH)(MeN)PPh (9), and C6H4(NH)(MeN)P(S)Ph (10) with PhPCl2, Ph2PCl, and PhP(Et2N)Cl have been examined. Reaction of 9 with PhPCl2/Et3N yields 1:1 threo- (14a) and erythro-chlorodiphosphazane (14b) C6H4(MeN)[NP(Cl)Ph]PPh, and 5:1 threo,threo-meso (15a) and d,l(15b) isomers of triphosphosphazane [C6H4(N)(MeN)PPh]2PPh. Reactions of 7/PhPCl2/Et3N or 7/PhP(Et2N)Cl yield 1:1 mixtures of the highly reactive chlorodiphosphazanes threo- (13a) and erythro- C6H4(NH)[NP(Cl)Ph]PPh (13b); 7 with Ph2PCl/Et3N forms C6H4(NH)(NPPh2)PPh (11) and C6H4(NPPh2)2PPh (12). Phosph(V)adiazole 8 with PhPCl2/Et3N yields one isomer of C6H4(NH)[NP(Cl)Ph]P(S)Ph (17) and a 2:1 mixture of one meso (18a) and the d,l(18b) isomer of triphosphazane C6H4[NP(Cl)Ph]2P(S)Ph; the 8/Ph2PCl reaction forms C6H4(NPPh2)2P(S)Ph (16). The 10/PhPCl2/Et3N reaction produces 5:1 threo- (19a) and erythro- C6H4(MeN)[NP(Cl)Ph]P(S)Ph (19b). Compounds 11-19 were characterized by spectral data; absolute stereochemistry of 15a was determined by X-ray analysis : triclinic, P1BAR, a = 10.369(2) angstrom, b = 12.326(3) angstrom, c = 12.682(6) angstrom, alpha = 76.58(3)degrees, beta = 70.52(3)degrees, gamma = 81.11(2)degrees, V = 1481.1 (8) angstrom3, Z = 2, R = 0.0526, R(w) = 0.0648. The stereochemistry of 19a was established from X-ray analysis of its molybdenum complex C6H4(MeN)[NP(Cl)Ph]P(S)PhMo(CO)4 (20a) : monclinic, P2(1)/c, a = 11.056(2) angstrom, b = 11.991(3) angstrom, c = 19.583(3) angstrom, beta = 100.310(10)degrees, V= 2554.2(7) angstrom3, Z = 4, R = 0.0413, R(w) = 0.0493. Although chlorodiphosphazane formation from phosph(III)adiazole chlorophosphination is nonselective, the analogous reaction involving phosph(V)diazoles is selective, favoring threo isomer formation. Comparison of skeletally stabilized phosphazane formation is made to that of previously reported acyclic analogs. Implications of the observed stereoselectivity for higher skeletally stabilized phosphazane formation are discussed.