Synthesis and Molecular Structure of Methylsllane- and Methylsiloxane-Cyclotrlphosphazenes¹

(Methylsilyl)- and (methylsiloxy)chlorocyclotriphosphazenes of formula N₃P₃C1₅R (1), gem-N₃P₃Cl₄R₂(2), and gem-N₃P₃Cl₄(Me)R (3) have been synthesized, where R = -CH₂SiMe₃, -CH₂SiMe₂OSiMe₃, or -CH₂Si(Me)-(0SiMe₂)₃-0. Compounds 1 and 2 are formed by the reactions of RMgCl with (NPC1₂)₃in THF at 66 °C. Species 3 were prepared either by the reaction of 1 with MeMgCl in THF at 25 °C or by the reaction of (NPC1₂)₃with MeMgCl/[(n-Bu)₃PCuI]₄at -78 °C, followed by the addition of RI. The chlorine atoms in 1–3 could be replaced by trifluoroethoxy groups in the presence of sodium trifluoroethoxide. Cleavage of the PCH₂-Si bond by sodium trifluoroethoxide also occurred under certain reaction conditions, especially when R was -CH₂Si(Me)-(0SiMe₂)₃-0. The mechanisms of these reactions are discussed. The crystal and molecular structures of 1, 2, and 3, where R = -CH₂Si(Me)-(0SiMe₂)₃-0, have been investigated by single-crystal X-ray diffraction. The phosphazene rings are puckered and have a nonsymmetric inequality of the skeletal bonds. Crystals of 2c are triclinic with space group PI, with a = 11.002 (4) A, b = 15.148 (3) A, c = 15.315 (3) A, a = 117.71 (1)°, β = 97.36 (1)°, and γ = 96.33 (1)°, with V = 2198.6 A²and Z = 2. Crystals of 3c are monoclinic with space group P2_1/c, with a = 14.847 (2) A, b = 8.620 (2) A, c = 22.828 (3) A, β = 100.59 (1)°, with V = 2871.8 A³and Z - 4. Crystals of lc were isomorphous with those of 3c.