Metal-Metal Multiple Bonds in Organometallic Compounds. I. (Di-ie/-/-butylacetylene)hexacarbonyldiiron and -dicobalt

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Metathetic reactions involving a variety of tungsten halides and LiNMe2 lead to W2(NMea)6, W(NMe2)e, and mixtures of these dimethylamides depending on the tungsten halides used. Pure W2(NMe2)é, free from W(NMe2)e, is prepared from the reaction of WCU with LiNMe2 (4 equiv). The related compounds W2(NMeEt)é and W2(NEt2)e are prepared by similar reactions. These tungsten(III) dialkylamides are pale-yellow, diamagnetic crystalline solids and have been characterized by a number of physical techniques including variable temperature NMR spectroscopy, infrared and Raman spectroscopy, and mass spectroscopy. Two compounds have been studied crystallographically. A substance consisting of W2(NMe2)s molecules and W(NMe2)é molecules in a 2:1 ratio crystallizes in the space group Pi, with unit cell dimensions: a = b = 13.556(2),_c = 9.420 (2) Á; V = 1499.6 (5) Á3. The W(NMe2)e molecule occupies the crystallographic position 0, 0, V2 with symmetry 3. The dimensions agree well with those previously determined for the pure W(NMe2)é phase. The W2(NMe2)6 molecules occupy the V3, %, z and %, V3, z positions with crystallographic symmetry 3. The W-W distance is 2.294 (1) Á; the mean W-N distance and mean W-W-N angles are, respectively, 1.98 Á and 103.8°. The structure was refined to R1 = 0.047 and T?2 = 0.061 using 4531 reflections having 7 > 3 ( ). Crystals consisting entirely of W2(NMe2)ó molecules belong to space group P2\/c (isomorphous with the corresponding Mo compound) with unit cell dimensions of a = 11.465 (3) Á, b = 11.948 (3) Á, c = 15.409 (3) Á, ß = 101.84 (2)°, and V = 2065.9 (8) Á3. There are two crystallographically independent molecules, each having crystallographic symmetry I but virtual symmetry which deviates only slightly from 3m (Du) and even less from 3 (Se). In these molecules the W-W distances are 2.290 (2) and 2.294 (2) Á. The mean values of the W-N distance and the W-W-N angles in both molecules are, respectively, 1.97 Á and 103.3°. This structure was refined to R¡ = 0.055 and T?2 = 0.067 using 1521 reflections having 7 > 3 (7).

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