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

Abstract

The syntheses, and spectroscopic, structural and electrochemical properties of cis -dioxotungsten(VI) complexes LWO 2 X [L = hydrotris(3,5-dimethylpyrazol-1-yl)borate; X = Cl -, NCS -, OMe -, O 2 CH -, OPh -, SPh -, S 2 PPh 2 - S -, SePh - ] are described. Reaction of LWO 2 Cl with group 1 salts M I X and 18-crown-6 in refluxing toluene was employed in the syntheses of derivatives with X = NCS -, OPh -, SPh -, and SePh -, while reaction of LWO 2 (SePh) with methanol and LWO 2 (SPh) with formic acid yielded LWO 2 (OMe) and LWO 2 (O 2 CH), respectively. The complex LWO 2 (S 2 PPh 2 - S ) was prepared by reacting LW(S 2 PPh 2 - S )(CO) 2 with pyridine N -oxide. The complexes exhibit two ν(WO 2 ) infrared bands, at 935−960 cm - 1 and 900−915 cm - 1, and 1 H NMR spectra consistent with C s symmetry. Orange crystals of cis -LWO 2 (SePh) are monoclinic, space group P 2 1 / c, with a = 18.385(6) Å, b = 8.102(1) Å, c = 18.284(5) Å, β = 117.15(2)°, V = 2423(2) Å 3, 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.