Aston A. Eagle

Paramagnetic oxotungsten(V) complexes containing the hydrotris(3,5-dimethylpyrazol-1-yl)borate ligand.

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.

Facets of Induced Internal Redox Involving WS42– and WSe42–: Synthesis and X-Ray Crystal Structures of syn-W2S2(μ-S)2(S2PPh2)2 and WO(Se2)(S2CNEt2)2

Reaction of (NEt4)2[WS4] and [S2PPh2]2 in acetonitrile results in the formation of diamagnetic, orange syn-W2S2(µ-S) 2(S2PPh2)2 by an induced internal redox process. Crystals of the toluene solvate W2S2(µ-S) 2(S2PPh2)2 . C7H8 are triclinic and belong to space group P1– with a 13.845(5), b 16.536(7), c 8.387(2) A, α 99.75(3), β 95.51(3), γ 83.08(3)˚, and Z 2. Refinement of 5445 data converged at R 0.038 and Rw 0.038. The complex possesses a syn-[W V 2S2(µ-S)2]2+ core with a W–W bond of 2.8161(5) A and two terminal W=S bonds of 2.097(3) and 2.096(3) A. The W-(µ-S) bond distances are in the range 2.310(2)–2.315(2) A. Each of the five-coordinate, square-pyramidal tungsten atoms is further coordinated by a bidentate dithiophosphinate ligand with W–S bond distances ranging from 2.464(2) to 2.481(2) A. Extended reaction of (NH4)2[WSe4] and [S2CNEt2]2 in acetonitrile produces green WS(Se2)(S2CNEt2)2 and red WO(Se2)(S2CNEt2)2 in 40% and 15% yields, respectively. Crystals of WO(Se2)(S2CNEt2)2 are monoclinic and belong to space group P21/n with a 9.609(6), b 15.053(7), c 13.120(9) A, β 100.08(4)˚, and Z 4. Refinement of 2473 data converged at R 0.039 and Rw 0.039. The seven-coordinate, pentagonal bipyramidal complex features C1 symmetry, an axial oxo ligand (W=O 1.705(6) A), an equatorial, side-on bonded diselenido ligand (W–Se(1) 2.509(1), W–Se(2) 2.547(1) A, Se(1)–Se(2) 2.306(2) A) and two bidentate dithiocarbamate ligands.

Tp*WIVO(S2CNEt2): the Missing Member of the Series

The missing member of the series Tp*ME(S2CNEt2) (M = Mo, W; E = O, S), namely Tp*WO(S2CNEt2), has been synthesized by oxygen-atom transfer from pyridine N-oxide to Tp*W(S2CNEt2)(CO)2. The air-stable, blue-purple complex was characterized by microanalysis, mass spectrometry (m/z 645 (100%), [M]+), cyclic voltammetry, and IR and 1H NMR spectroscopy. Solutions of the complex are dichroic and solvatochromic. The X-ray crystal structure of the complex revealed a six-coordinate, distorted octahedral complex with axial oxo (W = O 1.680(5) A), ‘equatorial’ dithiocarbamate (W—S 2.3962(17) and 2.4102(17) A), and facial tridentate Tp* ligands. The synthesis and characterization of Tp*WCl3 are also reported.

Mononuclear Sulfido-Tungsten(V) Complexes: Completing the Tp*MEXY (M = Mo, W; E = O, S) Series.

Orange Tp*WSCl2 has been synthesized from the reactions of Tp*WOCl2 with boron sulfide in refluxing toluene or Tp*WS2Cl with PPh3 in dichloromethane at room temperature. Mononuclear sulfido-tungsten(V) complexes, Tp*WSXY {X = Y = Cl, OPh, SPh, SePh; X = Cl, Y = OPh; XY = toluene-3,4-dithiolate (tdt), quinoxaline-2,3-dithiolate (qdt); and Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate} were prepared by metathesis of Tp*WSCl2 with the respective alkali metal salt of X-/XY2-, or [NHEt3]2(qdt). The complexes were characterized by microanalysis, mass spectrometry, electrochemistry, and infrared (IR), electron paramagnetic resonance (EPR) and electronic absorption spectroscopies. The molecular structures of Tp*WS(OPh)2, Tp*WS(SePh)2, and Tp*WS(tdt) have been determined by X-ray crystallography. The six-coordinate, distorted-octahedral W centers are coordinated by terminal sulfido (W≡S = 2.128(2) - 2.161(1) Å), terdentate facial Tp*, and monodentate/bidentate O/S/Se-donor ligands. The sulfido-W(V) complexes are characterized by lower energy electronic transitions, smaller giso, and larger Aiso(183W) values, and more positive reduction potentials compared with their oxo-W(V) counterparts. This series has been probed by sulfur K-edge X-ray absorption spectroscopy (XAS), the spectra being assigned by comparison to Tp*WOXY (X = Y = SPh; XY = tdt, qdt) and time-dependent density functional theoretical (TD-DFT) calculations. This study provides insight into the electronic nature and chemistry of the catalytically and biologically important sulfido-W unit.

Organometallic dioxo-, and oxo-thio- and dithio-tungsten(VI) complexes of hydrotris(3,5-dimethylpyrazolyl)borate

Reactions of cis-[{HB(Me2pz)3}WO2Cl] with Grignard reagents RMgX (R = Me, Et, CH2Ph, Ph; X = Cl or Br) in tetrahydrofuran, or boron sulfide in refluxing 1,2-dichloroethane, result in the formation of organometallic dioxo-WVI complexes, cis-[{HB(Me2pz)3}WO2R], and oxo-thio- and dithio-WVI complexes, cis-[{HB(Me2pz)3}WE2Cl](E2= OS, S2), respectively; the X-ray crystal structure of cis-[{HB(Me2pz)3}WO2Et], a rare example of a complex stable towards β-hydrogen elimination, is reported.