title: Paramagnetic oxotungsten(V) complexes containing the hydrotris(3,5-dimethylpyrazol-1-yl)borate ligand.
abstract: Sky-blue Tp*WOCl(2) has been synthesized from the high-yielding reaction of Tp*WO(2)Cl with boron trichloride in refluxing toluene. Dark-red Tp*WOI(2) was prepared via thermal decarbonylation followed by aerial oxidation of Tp*WI(CO)(3) in acetonitrile. From these precursors, an extensive series of mononuclear tungstenyl complexes, Tp*WOXY [X = Cl(-), Y = OPh(-), SPh(-); X = Y = OPh(-), 2-(n-propyl)phenolate (PP(-)), SPh(-), SePh(-); XY = toluene-3,4-dithiolate (tdt(2-)), quinoxaline-2,3-dithiolate (qdt(2-)), benzene-1,2-diselenolate (bds(2-)); Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate], was prepared by metathesis with the respective alkali-metal salt of X(-)/XY(2-) or (NHEt(3))(2)(qdt). The complexes were characterized by microanalysis, mass spectrometry, electrochemistry, IR, electron paramagnetic resonance (EPR), and electronic absorption spectroscopies, and X-ray crystallography (for X = Y = OPh(-), PP(-), SPh(-); XY = bds(2-)). The six-coordinate, distorted-octahedral tungsten centers are coordinated by terminal oxo [W≡O = 1.689(6)-1.704(3) Å], tridentate Tp*, and monodentate or bidentate O/S/Se-donor ligands. Spin Hamiltonian parameters derived from the simulation of fluid-solution X-band EPR spectra revealed that the soft-donor S/Se ligand complexes had larger g values and smaller (183)W hyperfine coupling constants than the less covalent hard-donor O/Cl species. The former showed low-energy ligand-to-metal charge-transfer bands in the near-IR region of their electronic absorption spectra. These oxotungsten(V) complexes display lower reduction potentials than their molybdenum counterparts, underscoring the preference of tungsten for higher oxidation states. Furthermore, the protonation of the pyrazine nitrogen atoms of the qdt(2-) ligand has been examined by spectroelectrochemistry; the product of the one-electron reduction of [Tp*WO(qdtH)](+) revealed usually intense low-energy bands.
authors.affiliation: School of Chemistry, University of Melbourne, Victoria 3010, Australia. sproules@mpi-muelheim.mpg.de
authors.forename: Stephen
authors.initials: S
authors.lastname: Sproules
authors.forename: Aston A
authors.initials: AA
authors.lastname: Eagle
authors.forename: Michelle K
authors.initials: MK
authors.lastname: Taylor
authors.forename: Robert W
authors.initials: RW
authors.lastname: Gable
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: White
authors.forename: Charles G
authors.initials: CG
authors.lastname: Young
mesh_terms: D000097:Acetonitriles / Q000737:chemistry; D005075:Biological Evolution; D001880:Boranes / Q000737:chemistry; D001881:Borates / Q000138:chemical synthesis* / Q000378:metabolism; D002712:Chlorides / Q000737:chemistry; D003116:Color; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D004583:Electrons; D008024:Ligands; D008280:Magnetics; D013058:Mass Spectrometry; D008958:Models, Molecular; D008982:Molybdenum / Q000737:chemistry*; D010084:Oxidation-Reduction; D011720:Pyrazoles / Q000138:chemical synthesis* / Q000378:metabolism; D014414:Tungsten / Q000737:chemistry*
chemical_list: D000097:Acetonitriles; D001880:Boranes; D001881:Borates; D002712:Chlorides; D008024:Ligands; D011720:Pyrazoles; D008982:Molybdenum; C092267:boron trichloride; D014414:Tungsten; C032159:acetonitrile