Darin B. Tiedtke

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

Abstract 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(C6H5N)2 and W2(OtBu)6(4-CH3C6H4N)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-tolycarbodiimide 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(OCMe2CF3)6. Also W2(OCMe2CF3)6 and W2(OSitBuMe2)6 bind two equivalents of xylylisocyanide to afford W2(OR)6(η1-CNAr)2. For W2(OCMe2CF3)6(η1-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 of 105–114°, the WWC angles are 83(1)°. Similarly, W2(OCMe(CF3)2)4(NMe2)2 forms a bis adduct upon reaction with the isocyanide. However, the molecular structure of W2(OCMe(CF3)2)4(NMe2)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  t Bu , t BuMe 2 Si and Cme 2 CF 3 .

Organometallic Chemistry of [W2(OCH2tBu)8] (M=M): Substrate Uptake and Activation at a Tungsten–Tungsten Double Bond

The 1:1 adducts of [W2(OCH2tBu)8] with ethyne, allene, carbon monoxide, and benzophenone have been characterized by 1H, 13C NMR, and IR spectroscopy, and elemental analysis. The structures of the ethyne and allene adducts were also characterized by single-crystal X-ray crystallography. Their reactivity is compared with that of related [W2(OR)6](M≡M) compounds and with that of M=M-bonded species such as [Cp*2Re2(CO)4] and “[Os2(CO)8]”.

Preparation, characterization and electronic structure of W2(NMe2)2(ORf)4, where Rf = CMe2CF3, CMe(CF3)2 and C(CF3)3, as deduced by photoelectron spectroscopic studies and the single crystal X-ray structure for Rf = OCMe(CF3)2

Abstract The compounds of W2(NMe2)2(OCMe2CF3)4, 1, W2(NMe2)2(OCMe(CF3)2)4, 2, and W2(NMe2)2 (OC(CF3)3)4, 3, have been obtained from reactions between W2(NMe2)6 and the respective fluoroalcohol in hydrocarbon solvents. The compounds 2 and 3 appear inert to further reaction with their fluoroalcohol at room temperature while 1 reacts further to give W2(OCMe2CF3)6. In solution NMR data indicate that all three compounds exist in a mixture of anti- and gauche-rotamers with restricted rotations about both WN and WW bonds on the NMR time-scale. The solid-state molecular structure of 2 reveals a centrosymmetric NO2WWO2N core with W  W = 2.3107(6) A , W z.sbnd; N = 1.914(4) A , W  O = 1.959(3) aand 1.907(3) A and angles WWO/N within the range 100 to 110°. The gas phase photoelectron spectra for 1, 2 and 3 were obtained and are compared with that for W2(NMe2)6. The introduction of the fluoroalkoxide ligands has a pronounced effect in stabilizing the metal and nitrogen lone-pair based ionizations, and this effect is amplified by the successive replacement of each methyl group by a trifluoromethyl group. Also for the compounds 1, 2, and 3 the lowest ionization bands clearly reveal the removal of the degeneracy of the WW π MOs as expected for anti and gauche complexes.