Cyclotriphosphazenes with Geminal (Trimethylsilyl)methyl and Alkyl or Aryl Side Groups

The synthesis of a series of organosilyl cyclophosphazenes of formula gem-N₃P₃Cl₄(CH₂SiMe₃)(R), where R = C₂H₅, i-C₃H₇, n-C₄H₉, t-C₄H₉, neo-C₅H₁₁, and C₆H₅, via organometallic reactions, is described. The chlorine atoms in the cyclic trimers were replaced by trifluoroethoxy groups by reactions that led to either retention of the (trimethylsilyl)methyl units or replacement of them by methyl groups, depending on the reaction conditions. The crystal and molecular structures of gem-N₃P₃Cl₄-(CH₂SiMe₃)(t-C₄H₉) and the related derivative gem-N₃P₃Cl₄(CH₂SiMe₃)₂ were determined by single-crystal X-ray diffraction methods. Steric hindrance involving the organosilyl units results in a widening of the external angle at the supporting phosphorus atom and a narrowing of the corresponding ring angle at that site. Crystals of gem-N₃P₃Cl₄(CH₂SiMe₃)(t-C₄H₉) are orthorhombic with space group Pbca, with a = 14.884 (4) Å, b = 15.815 (4) Å, c = 16.615 (4) Å, V = 3910.9 ų, and Z = 8. Crystals of gem-N₃P₃Cl₄(CH₂SiMe₃)₂ are monoclinic with space group P2₁/n, with a = 10.145 (4) Å, b = 11.060 (5) Å, c = 19.999 (6) Å, β = 103.56 (3)°, V = 2181.4 ų, and Z = 4.