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.

Significant differences of monooxotungsten(iv) and dioxotungsten(vi) benzenedithiolates containing two intramolecular NH⋯S hydrogen bonds from molybdenum analogues

“…3,11 Comparative model studies are very important to understand the nature of W and Mo enzymes. 2,[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] Comprehensive studies have been reported in a review. 2 In the case of square-pyramidal monooxo bis(dithiolate) complexes, the bond length of the multiple WuO bond is longer than that of the MouO bond, although the bond dissociation energy of WuO is larger than that of MouO.…”

Spontaneous Formation of an η2‐C, S‐Thioketene Complex in Pursuit of Tungsten(IV)‐Sulfanylalkyne Complexes

“…However, further evidence is provided by mass spectrometry, which clearly shows the molecular peak at 659 m / z . The related dihalide species [Tp′W(O)( X ) 2 ] ( X = Cl, I) were already synthesized, characterized, and examined by spectroelectrochemistry showing specific absorption in the UV/Vis region 12. As reported by Young , the dichlorido complex is sky‐blue, whereas the diiodido complex is dark red.…”

Four-Component Relativistic Density Functional Calculations of EPR Parameters for Model Complexes of Tungstoenzymes

“…A variety of possible solvents (CH 2 Cl 2 , DMF, and THF) were mentioned for the EPR measurements of [Tp*WO(XPh) 2 ] (X = O, S), without further specifying the one actually used. 41 EPR Parameter Calculations. The four-component relativistic mDKS method with restricted kinetically balanced (RKB) 42,43 basis sets is the DFT analogy of the modified Dirac equation 44,45 and has been described previously.…”

“…For [WO­(bdt) 2 ] − , a DMF/CH 3 CN “mixture” with ε = 36.4 is used. A variety of possible solvents (CH 2 Cl 2 , DMF, and THF) were mentioned for the EPR measurements of [Tp*WO­(XPh) 2 ] (X = O, S), without further specifying the one actually used …”