Facile Reduction of Tungsten Halides with Nonconventional, Mild Reductants. I. Tungsten Tetrachloride: Several Convenient Solid-State Syntheses, a Solution Synthesis of Highly Reactive (WCI4)x, and the Molecular Structure of Polymeric Tungsten Tetrachloride

Abstract

Polymeric (WCl4)X has been prepared in crystalline form from WCl6 by three new, safer solid-state approaches via mercury (in 83% yield), bismuth (82% yield), or antimony (97% yield) reduction. A modification of a published procedure for reduction of WCl6 with red phosphorus, which improves (WCl4)x purity, is also described. Highly reactive (WCl4)xpowder can be prepared in 99% yield via tin reduction of WCl6 in 1,2-dichloroethane. (WCl4)x powder was readily converted in high yields to the known WCl4(MeCN)2 and W2Cl4(OMe)4(HOMe)2. The molecular structure of (WCl4)x, as determined by single-crystal X-ray diffractometry, consists of a polymer of opposite-edge-sharing bioctahedra with alternating short (W(1)-W(1A), 2.688(2) Å) and long (W(1)⋯W(1B), 3.787(3) Å) tungsten - tungsten distances. The acute W(1)-Cl(2)-W(1A) angle (69.4(2)°), obtuse C1(1)-W(1)W(1A) angle (94.99(12)°), short axial Cl(1)⋯Cl(1A) nonbonded distance (3.085(10) Å, substantially less than twice the Cl van der Waals radius), and short W(1)-W(1A) distance are consistent with a strong W(1)-W(1A) interaction best described as a W=W bond for this d2-d2 compound. Crystal data: Cl4W, a = 11.782(3) Å, b = 6.475(1) Å, c = 8.062(2) Å, β= 131.14(1)°, V = 463.2(2) Å3, monoclinic, C2/m, Z = 4.