Di-iodine oxidation of molybdenum(0)–η6-arene complexes. New results on molybdenum(II) and tungsten(II) carbonyl derivatives; crystal structures of [Ml(CO)3(η6-C6H3Me3-1,3,5)][M2I5(CO)6](M = Mo or W) and [Mol(CO)3(η6-C6Me6)][Mol3(CO)4]

Abstract

The reactions of molybdenum(0) complexes with I₂ have been investigated under a variety of reaction conditions and stoicheiometry of the reagents, and shown to be more complicated than previously suggested. Although the [Mol (CO)₃(η⁶-arene)]⁺ cation is always formed, the counter anion can vary depending on the reaction time and on the molar ratio of the reagents. Some of the isolated compounds were studied by X-ray diffractometric methods: [Mol (CO)₃(η⁶-C₆H₃Me₃-1,3,5)][Mo₂I₅(CO)₆], (3)[monoclinic, space group P2₁/c, a= 13.632(2), b= 13.758(2), c= 17.246(3)Å, β= 96.02(2)°, and Z= 4], the new [Mo₂I₅(CO)₆]^– anion has approximately C_2v symmetry, the central metal atoms being seven-co-ordinated by three bridging iodides, one terminal iodide and three carbonyl groups; [Mol (CO)₃(η⁶-C₆Me₆)][Mol₃(CO)₄], (5)[monoclinic, space group P2₁/a, a= 24.01 3(3), b= 13.681(3), c= 8.797(3)Å, β= 97.86(2)°, and Z= 4]. When the reaction between [Mo(CO)₃(η⁶-C₆Me₆)] and di-iodine was carried out in a 1 : 2 molar ratio, the tri-iodide complex [Mol(CO)₃(η⁶-C₆Me₆)]I₃ was isolated, while the reaction of [W(CO)₃(η⁶C₆H₃Me₃-1,3,5)] with di-iodine in a 1 : 1 molar ratio gave the tungsten(II) derivative [Wl(CO)₃(η⁶-C₆H₃Me₃-1,3,5)][W₂I₅(CO)₆], (8)[monoclinic, space group P2₁/c, a= 13.602(2), b= 13.720(2), c= 17.204(3)Å, β= 95.99(2)°, and Z= 4]. Compounds (3) and (8) are isostructural. The problem of the arene orientation in the [Ml(CO)₃(η⁶-arene)]⁺ cations is discussed.