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. Pyridi ne binds more strongly to the fluoroalkoxide but the structural parame ters of the compounds W-2(OCMe2CF3)(6)(C6H5N)(2) and W-2(O'Bu)(6)(4-CH 3C6H4N)(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. Bot h 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 t he 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 (OCMe2C F3)(6) and W-2(OSi'BuMe2)(6) bind two equivalents of xylylisocyanide t o 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 crystallogra phy and shows a nearly eclipsed central W2O6C2 skeleton with W-W = 2.4 4(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 a ngles are 83(1)degrees. Similarly, W-2(OChle(CF3)(2))(4)(NMe2)(2) form s a bis adduct upon reaction with the isocyanide. However, the molecul ar 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 = 1.9 3(1) Angstrom (av.) and W-C = 2.14(1) Angstrom (av.) with a C-W-W-C di hedral angle of 41.9 degrees. These reactions and their products are c ompared for W-2(OR)(6) compounds where R = 'Bu,'BuMe2Si and CMe2CF3. ( C) 1998 Elsevier Science Ltd. All rights reserved.