Synthesis and characterisation of tungsten siloxides including the crystal structure of [WO{O(Ph2SiO)3}2(thf)]

Reactions of WOCl4 with NaOSiPh3 and Na2O2SiPh2 gave respectively [WO(Cl)(OSiPh3)(3)] and [{WO2[(OSiPh2)(2)O]}(2)]. Under similar conditions NaOSiPh3 reacted with [WO2Cl2(OSC4H8)(2)] to yield [WO2(OSiPh3)(2)(OSC4H8)(2)]. The novel spirocyclic tungstasiloxane [WO{O(Ph2SiO)(3)}(2)(thf)] was prepared from the reaction between equimolar quantities of (Ph2SiO)(3) and WOCl4 in tetrahydrofuran. A crystal structure determination on this product revealed a distorted octahedral geometry about the central tungsten atom with the axially co-ordinated ether ligand trans to the oxo group, and puckered eight-membered siloxane rings oriented on opposite sides of the equatorial plane defined by the four co-ordinated siloxide O atoms. The W-O (Si) separations ranged from 1.851(7) to 1.896(8) Angstrom and the W=O bond length was 1.675(13) Angstrom. In dichloromethane WCl6 reacted with (Ph2SiO)(3) to afford good yields of WOCl4, whereas in tetrahydrofuran the same reactants caused solvent polymerisation.