Über die Reaktion von 2,2-Dimethylpropylidinphosphan mit Wolframhexachlorid; die Kristallstrukturen von [(Cl3PO)WCl4(H9C4?CC?C4H9)] und [(H5C6)4As][WCl6]

Reaction of 2,2-Dimethylpropylidynephosphane with Tungsten Hexachloride as well as the Crystal Structures of (Cl₃PO)WCl₄(H₉C₄? C?C—C₄H₉)] and (H₅C₆)₄As]WCl₆] The reaction of 2,2-dimethylpropylidynephosphane, (CH₃)₃C? C?P|, with tungsten hexachloride suspended in POCl₃ results, with oxidation of the phosphorus atom, in 2,2,5,5-tetramethylhex-3-yne. This compound reacts with tungsten tetrachloride simultaneously formed to give the alkyne complex (Cl₃PO)WCl₄(H₉C₄? C?C—C₄H₉)], which is dark green in colour. A small amount of tungsten hexachloride is reduced merely to tungsten pentachloride; after the addition of tetraphenyl arsonium chloride it can be isolated as (H₅C₆)₄As]WCl₆]. For this compound, a new and very simple synthesis from WCl₆, (H₅C₆)₄As]Cl and C₂Cl₄ as reducing agent is described. The structure of (Cl₃PO)WCl₄(H₉C₄? C?C? C₄H₉)] has been determined from X-ray diffraction data (R = 5.8%). The complex crystallizes in the monoclinic space group P2₁/n with: {a = 1510; b = 1517; c = 849 pm; β = 93.1°; Z = 4}. The tungsten atom is sevenfold coordinated by four equatorial chlorine atoms, by the C°C group of the acetylene ligand and by the oxygen atom of the POCl₃ molecule in trans position. The bulky acetylene ligand which is nearly symmetrically bound shifts the chlorine atoms towards the solvated POCl₃ molecule so that no common plane with the tungsten atom is possible. With 130 pm the C°C bond length of the 2,2,5,5-tetramethyl-3-yne ligand corresponds to a C°C double bond. The i.r. spectrum of (H₅C₆)As]WCl₆] shows two WCl₆ strectching vibrations and therefore proves a reduction of octahedral symmetry. In agreement with the results of a crystal structure determination (space group P4/n; a = 1301; c = 780 pm; Z = 2.7%) the WCl₆]^?-anion has nearly exact C_4V symmetry with somewhat shorter W? Cl bond lengths parallel to the fourfold axis of rotation.