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.