The reduction of trans-[WCl4(PR3)2](PR3= tertiary phosphine) by sodium amalgam in tetrahydrofuran solution at ca. 20° under argon, dinitrogen, dihydrogen or carbon monoxide is discussed. The syntheses of hydrido-, dinitrogen, and carbonyl complexes are achieved by these routes. The interconversions and isomerisations of pentacarbonyl-, tetracarbonyl-, and tricarbonyl-tungsten complexes containing tertiary phosphines are described.