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

Abstract

Reactions of WOCl₄ with NaOSiPh₃ and Na₂O₂SiPh₂ gave respectively [WO(Cl)(OSiPh₃)₃] and [{WO₂[(OSiPh₂)₂O]}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) Å and the WO bond length was 1.675(13) Å. In dichloromethane WCl₆ reacted with (Ph₂SiO)₃ to afford good yields of WOCl₄, whereas in tetrahydrofuran the same reactants caused solvent polymerisation.