Di-iodine oxidation of molybdenum( 0 )–η 6 -arene complexes. New results on molybdenum( II ) and tungsten( II ) carbonyl derivatives; crystal structures of [Ml(CO) 3 (η 6 -C 6 H 3 Me 3 -1,3,5)][M 2 I 5 (CO) 6 ](M = Mo or W) and [Mol(CO) 3 (η 6 -C 6 Me 6 )][Mol 3 (CO) 4 ]

International audienceThe 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 C2v 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