Improved synthetic routes to tungsten(IV) bromide complexes

Abstract

Convenient synthetic routes to the compounds WBr4 (1), WBr4(MeCN)2 (2), WBr4(THF)2 (3), WBr4(PPh3)2 (4), WBr4(bpy) (6), and WBr4(dppe) (7) are described via the solution-phase oxidation of W(CO)6 using two equivalents of bromine. These one-pot syntheses use inexpensive and readily available starting materials and produce analytically pure compounds with high yields under mild conditions. Attempts to grow crystals of 1 by heating in a sealed tube at ~200 °C resulted in formation of the previously reported compound WOBr4. Attempts to recrystallize 4 from dichloromethane solution produced [HPPh3]2[WBr6] (5). X-ray crystallographic studies showed that 5 consists of an array of [WBr6]2− anions and [HPPh3]+ cations and that 7·CH2Cl2 has the expected six-coordinate tungsten center. The synthesis of tungsten(IV) bromide compounds via oxidation of W(CO)6 is simple and provides better yields than previously reported methods. This synthetic route also has many advantages over the syntheses of similar tungsten(IV) chloride compounds which involve reduction of WCl6.