Significant mechanistic differences exist between the reactions of mono-and dilithioferrocene or ruthenocene with P-F or P-CI bonds in cyclophosphazenes. The fluorophosphazenes (NPF2)3 and (NPF2)4 react by a nucleophilic-type substitution pathway to yield mono and bis nongeminal metallocenyl derivatives (6-9) or transannular bridged metallocenylphosphazenes (10-13). By contrast, the chlorophosphazene (NPCI,), reacts initially by a metal-halogen exchange pathway to generate an unusual series of metallocenyl cyclophosphazenes and -bi(cyclophosphazenes) (18-20), including examples in which chloro metallocene units are linked to phosphorus (21,22) and one in which a ferrocene unit bridges the P-P linkage site connecting two cyclophosphazene rings (23). Cleavage of the phosphazene skeleton occurs with (NPC12)4. The molecular structures of four ferrocenyl-and ruthenocenylcyclophosphazenes prepared by these routes have been determined by X-ray diffraction techniques. Confirmation of a covalent linkage between a cyclopentadienyl group and the phosphazene ring was obtained for the prototype, N3P3F5(q-C5H4)Fe(~-C5H5) (6a). The effect of transannular bridging of the phosphazene ring by metallocene units was studied in N 3 P 3 F 4 (~-C 5 H 4 ) 2 R~ (lob) and N4P4F6(~-C5H4),Ru (12b). The structure of species N,P6C18(q-C5H4),Fe (23), with two phosphazene rings linked by a P-P bond and a ferrocenyl bridging site, was also examined. The structural peculiarities are a consequence of the low deformability of the metallocenyl units and the relatively high flexibility of the phos hazene rings. Crystal data: Crystals of 6a are monoclinic with the space group C2/c, a = 19.946 (9) A, b = 6.922 (2) 1, c = 22.340 (9) A, p = 11 1.19 (S)', and V = 2876 (4) A3 and Z = 8. Crystals of 10b are triclinic with the space group Pi and with a = 8.029 (2) A, b = 8.286 (4) A, c = 11.555 (7) A, and CY = 87.16 ( 4 ) O , = 87.91 ( 3 ) O , y = 61.83 ( 3 ) O , and V = 676.7 (7) A3 and Z = 2. Crystals of 12b are orthorhombic with the space group Pbca and with a = 15.534 (3) A, b = 14.610 (3) A, c = 14.430 (2) A, and V = 3275 (2) A3 and Z = 8. Crystals of 23 are monoclinic with the space group P 2 , / n and with a = 11.064 (2) A, b = 13.019 (4) A, c = 18.196 (3) A, p = 102.55 (3)O, and V = 2558 (2) A' and Z = 4. The reactions of organometallic reagents with halophosphazenes
