Pyridine, isocyanide, carbodiimide and allene adducts of hexakis(trifluoromethyl t-botoxy)ditungsten. A comparison of ligand binding to W2(OtBu)6 and W2(OCMe2CF3)6

Article abstract of DOI:10.1016/S0277-5387(97)00290-8

W₂(OR)₆ compounds, where R = ^tBu and CMe²CF³, both reversibly bind pyridine in hydrocarbon solvents to form adducts W²(OR)⁶L₂. Pyridine binds more strongly to the fluoroalkoxide but the structural parameters of the compounds W₂(OCMe₂CF₃)₆(C₆H ₅N)₂ and W₂(O^tBu)₆(4-CH₃C₆H ₄N)₂ reveal an essentially identical W₂O₆N₂ core with W-W = 2.39(1) A, W-O = 1.92-1.95 A and W-N = 2.26(1) A. Both compounds were crystallographically characterized in the space group C2/c and each molecule has rigorous C₂ symmetry. Allene and 1,3-di-p-tolylcarbodiimide form 1 : 1 adducts with W₂(OCMe₂CF³)₆ in which the substrate is bound parallel to the M-M axis, i.e. μ-η²,η²-C₃H₄ and μ-η²,η²-ArNCNAr-W₂(OCMe ₂CF₃)₆. Also W₂ (OCMe₂CF₃)₆ and W₂(OSi^tBuMe₂)⁶ bind two equivalents of xylylisocyanide to afford W₂(OR)₆(η¹-CNAr)₂. For W₂(OCMe₂CF₃)₆(η ¹-CNAr)₂, the molecular structure has been determined by X-ray crystallography and shows a nearly eclipsed central W₂O₆C₂ skeleton with W-W = 2.44(1) A, W-O = 1.94(1) A (av.) and W-C = 2.14(1) A, whereas the W-W-O angles span the range 105-114°, the W-W-C angles are 83(1)°. Similarly, W₂(OCMe(CF₃)₂)₄(NMe ₂)₂ forms a bis adduct upon reaction with the isocyanide. However, the molecular structure of W₂(OCMe(CF₃)₂)₄(NMe ₂)₂(η¹-CNAr)₂ shows a staggered arrangement of the two ligands about the ditungsten center where W-W = 2.382(1) A, W-O = 2.00(1) A (av.), W-N = 1.93(1) A (av.) and W-C = 2.14(1) A (av.) with a C-W-W-C dihedral angle of 41.9°. These reactions and their products are compared for W₂(OR)₆ compounds where R = ^tBu, ^tBuMe₂Si and CMe₂CF₃.