Synthesis and Structure of Metallocene Cyclophosphazene Derivatives

Significant mechanistic differences exist between the reactions of mono- and dilithioferrocene or ruthenocene with P-F or P-Cl 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 (NPCl₂)₃ 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 (NPCl₂)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(η-C₅H₄)Fe(η-C₅H₄) (6a). The effect of transannular bridging of the phosphazene ring by metallocene units was studied in N₃P₃F₄(η-C₅H₄)₂Ru (10b) and N₄P₄F₆(η-C₅H₄)₂Ru (12b). The structure of species N₆P₆Cl₈(η-C₅H₄)₂Fe (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 phosphazene rings. Crystal data: Crystals of 6a are monoclinic with the space group C2/c, a = 19.946 (9) Å, b = 6.922 (2) Å, c = 22.340 (9) Å, β = H 1-19 (5)°, and V = 2876 (4) ų and Z = 8. Crystals of 10b are triclinic with the space group C2/c, a = 19.946 (9) Å, b = 6.92 (2) Å, c = 22.340 (9) Å, #x03B2; = 111.19 (5)°, and V = 2876 (4) ų and Z = 8. Crystals of 10b are triclinic with the space group PI and with a = 8.029 (2) Å, b = 8.286 (4) Å, c = 11.555 (7) Å, and α = 87.16 (4)°, β = 87.91 (3)°, γ = 61.83 (3)°, and V = 676.7 (7) ų and Z = 2. Crystals of 12b are orthorhombic with the space group Pbca and with a = 15.534 (3) Å, b = 14.610 (3) Å, c = 14.430 (2) Å, and V = 3275 (2) ų and Z = 8. Crystals of 23 are monoclinic with the space group P2₁/4 and with a = 11.064 (2) Å, b = 13.019 (4) Å, c = 18.196 (3) Å, β = 102.55 (3)°, and V = 2558 (2) ų and Z = 4.