Dioxotungsten(VI) Complexes of Hydrotris(3,5-dimethylpyrazol-1-yl)borate Including the X-ray Crystal Structure of the Tungsten Selenophenolate Complexcis-{HB(Me₂C₃N₂H)₃}WO₂(SePh)

Abstract

The syntheses, and spectroscopic, structural and electrochemical properties of cis-dioxotungsten(VI) complexes LWO2X [L = hydrotris(3,5-dimethylpyrazol-1-yl)borate; X = Cl-, NCS-, OMe-, O2CH-, OPh-, SPh-, S2PPh2-S -, SePh-] are described. Reaction of LWO2Cl with group 1 salts MIX and 18-crown-6 in refluxing toluene was employed in the syntheses of derivatives with X = NCS-, OPh-, SPh-, and SePh-, while reaction of LWO2(SePh) with methanol and LWO2(SPh) with formic acid yielded LWO2(OMe) and LWO2(O2CH), respectively. The complex LWO2(S2PPh2-S) was prepared by reacting LW(S2PPh2-S)(CO)2 with pyridine N-oxide. The complexes exhibit two ν(WO2) infrared bands, at 935−960 cm-1 and 900−915 cm-1, and 1H NMR spectra consistent with C s symmetry. Orange crystals of cis-LWO2(SePh) are monoclinic, space group P21/c, with a = 18.385(6) Å, b = 8.102(1) Å, c = 18.284(5) Å, β = 117.15(2)°, V = 2423(2) Å3, and Z = 4. The structure was solved by direct methods and refined to R = 0.035 (R w = 0.033) for 3668 reflections with I ≥ 3.0σ(I). The mononuclear complex exhibits a distorted octahedral coordination sphere composed of a selenophenolate ligand [W−Se = 2.535(1) Å], two terminal oxo groups [WO = 1.716(4) and 1.721(4) Å], and a facially tridentate L ligand. In acetonitrile, the complexes undergo a one-electron reduction at very cathodic potentials (E 1/2 = −1.71 to E pc = −1.05 V vs SCE), some 560−620 mV more negative than observed for analogous molybdenum complexes (Inorg. Chem. 1996, 35, 7508). The complexes are very stable and do not participate in clean oxygen atom transfer or coupled electron−proton transfer reactions.

Facets of early transition metal–sulfur chemistry: Metal–sulfur ligand redox, induced internal electron transfer, and the reactions of metal–sulfur complexes with alkynes

“…The M(VI)/M(V) reduction potentials of Tp * MoO 2 X complexes are ca. 400 mV more positive than their W counterparts [45]. The bis(sulfido)-W(VI) complexes react with alkynes to produce dithiolene ligand complexes (Section 4.…”

The Syntheses and Vibrational Spectra of 16O‐ and 18O‐Enriched cis‐MO2 (M=Mo, W) Complexes

“…Specifically, molecular complexes [MoO 2 (L n )] show two distinctive absorption maxima at 915–935 and 890–905 cm −1 , respectively, whereas complexes [WO 2 (L) n ] display typically two strong vibrational bands at ca . 930–960 and 870–920 cm −1 in their IR spectra ,,,. Generally, these two bands show a difference of 20–35 cm –1 .…”

Olefin Epoxidation by H2O2/MeCN Catalysed by Cyclopentadienyloxidotungsten(VI) and Molybdenum(VI) Complexes: Experiments and Computations

“…However, the well known catalytic activity of several peroxidotungstate systems is often greater than that of their molybdenum analogues. [13] The recent progress related to oxotransferase tungsten-containing enzymes [14][15][16][17][18][19][20] suggests that the investigation of olefin epoxidations catalysed by organometallic derivatives of the WO 2 fragment could be particularly rewarding. A higher catalytic activity of [Cp* 2 W 2 O 5 ] compared to the related Mo system has been recently underlined for the oxidation of thiophene derivatives.…”