PREPARATION, CHARACTERIZATION AND ELECTRONIC-STRUCTURE OF W-2(NME2)(2)(ORF)(4), WHERE R-F = CME2CF3, CME(CF3)(2) AND C(CF3)(3), AS DEDUCED BY PHOTOELECTRON SPECTROSCOPIC STUDIES AND THE SINGLE-CRYSTAL X-RAY STRUCTURE FOR R-F = OCME(CF3)(2)

The compounds W-2(NMe2)(2)(OCMe2CF3)(4), 1, W-2(NMe2)(2)(OCMe(CF3)(2)) (4), 2, and W-2(NMe2)(2) (OC(CF3)(3))(4), 3, have been obtained from r eactions between W-2(NMe2)(6) and the respective fluoroalcohol in hydr ocarbon solvents. The compounds 2 and 3 appear inert to further reacti on with their fluoroalcohol at room temperature while 1 reacts further to give W-2(OCMe2CF3)(6). In solution NMR data indicate that all thre e compounds exist in a mixture of anti- and gauche-rotamers with restr icted rotations about both W-N and W=W bonds on the NMR time-scale. Th e solid-state molecular structure of 2 reveals a centrosymmetric NO2W= WO2N core with W-W = 2.3107(6) Angstrom, W-N = 1.914(4) Angstrom, W-O = 1.959(3) and 1.907(3) Angstrom and angles W-W-O/N within the range 1 00 to 110 degrees. The gas phase photoelectron spectra for 1, 2 and 3 were obtained and are compared with that for W-2(NMe2)(6). The introdu ction of the fluoroalkoxide ligands has a pronounced effect in stabili zing the metal and nitrogen lone-pair based ionizations, and this effe ct 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 pi MOs as expected for anti and gauche complexes. (C) 1998 Elsevie r Science Ltd. All rights reserved.