Pyridine, isocyanide, carbodiimide and allene adducts of hexakis(trifluoromethyl t-botoxy)ditungsten. A comparison of ligand binding to W-2((OBu)-Bu-t)(6) and W-2(OCMe2CF3)(6)
W-2(OR)(6) compounds, where R = 'Bu and CMe2CF3, both reversibly bind pyridine in hydrocarbon solvents to form adducts W-2(OR)(6)L-2. Pyridine binds more strongly to the fluoroalkoxide but the structural parameters of the compounds W-2(OCMe2CF3)(6)(C6H5N)(2) and W-2(O'Bu)(6)(4-CH3C6H4N)(2) reveal an essentially identical W2O6N2 core with W-W = 2.39(1) Angstrom, W-O = 1.92-1.95 Angstrom and W-N = 2.26(1) Angstrom. Both compounds were crystallographically characterized in the space group C2/c and each molecule has rigorous C-2 symmetry. Allene and 1,3-di-p-tolylcarbodiimide form 1 : 1 adducts with W-2(OCMe2CF3)(6) in which the substrate is bound parallel to the M-M axis, i.e. mu-eta(2), eta(2)-C3H4 and mu-eta(2), eta(2)-ArNCNAr-W-2(OCMe2CF3)(6). Also W-2 (OCMe2CF3)(6) and W-2(OSi'BuMe2)(6) bind two equivalents of xylylisocyanide to afford W-2(OR)(6)(eta(1)-CNAr)(2). For W-2(OCMe2CF3)(6)(eta(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) Angstrom, W-O = 1.94(1) Angstrom (av.) and W-C = 2.14(1) Angstrom, whereas the W-W-O angles span the range 105-114 degrees, the W-W-C angles are 83(1)degrees. Similarly, W-2(OChle(CF3)(2))(4)(NMe2)(2) forms a bis adduct upon reaction with the isocyanide. However, the molecular structure of W-2(OCMe(CF3)(2))(4)(NMe2)(2)(eta(1)-CNAr)(2), shows a staggered arrangement of the two ligands about the ditungsten center where W-W = 2.382(1) Angstrom, W-O = 2.00(1) Angstrom (av.), W-N = 1.93(1) Angstrom (av.) and W-C = 2.14(1) Angstrom (av.) with a C-W-W-C dihedral angle of 41.9 degrees. These reactions and their products are compared for W-2(OR)(6) compounds where R = 'Bu,'BuMe2Si and CMe2CF3. (C) 1998 Elsevier Science Ltd. All rights reserved. [References: 15]
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