DIASTEREOSELECTIVITY IN THE FORMATION OF SKELETALLY STABILIZED PHOSPHAZANES

Skeletally stabilized di- and triphosphazane formation and stereoselec tion 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 PhPCl 2/Et3N yields 1:1 threo- (14a) and erythro-chlorodiphosphazane (14b) C 6H4(MeN)[NP(Cl)Ph]PPh, and 5:1 threo,threo-meso (15a) and d,l(15b) iso mers of triphosphosphazane [C6H4(N)(MeN)PPh]2PPh. Reactions of 7/PhPCl 2/Et3N or 7/PhP(Et2N)Cl yield 1:1 mixtures of the highly reactive chlo rodiphosphazanes 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 r eaction forms C6H4(NPPh2)2P(S)Ph (16). The 10/PhPCl2/Et3N reaction pro duces 5:1 threo- (19a) and erythro- C6H4(MeN)[NP(Cl)Ph]P(S)Ph (19b). C ompounds 11-19 were characterized by spectral data; absolute stereoche mistry 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, al pha = 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 ster eochemistry of 19a was established from X-ray analysis of its molybden um 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) angstro m, beta = 100.310(10)degrees, V= 2554.2(7) angstrom3, Z = 4, R = 0.041 3, R(w) = 0.0493. Although chlorodiphosphazane formation from phosph(I II)adiazole chlorophosphination is nonselective, the analogous reactio n involving phosph(V)diazoles is selective, favoring threo isomer form ation. Comparison of skeletally stabilized phosphazane formation is ma de to that of previously reported acyclic analogs. Implications of the observed stereoselectivity for higher skeletally stabilized phosphaza ne formation are discussed.