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

Abstract

Orange Tp*WSCl has been synthesized from the reactions of Tp*WOCl with boron sulfide in refluxing toluene or Tp*WSCl with PPh 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*WSCl with the respective alkali metal salt of X/XY, or [NHEt](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), Tp*WS(SePh), 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 g, and larger A(W) 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.

Oxo versus Sulfido Coordination at Tungsten: A Spectroscopic and Correlated Ab Initio Electronic Structure Study

“…13 Direct conversion to Tp*WSCl 2 can be achieved with boron sulfide, though treating a dichloromethane solution of Tp*WS 2 Cl with triphenylphosphine generates the sulfido analogue in higher yield. 12 For Tp*WOCl 2 , there is a crystal structure, though the metrics are of limited value on account of the crystallographic mirror plane that disorders the position of the oxo ligand with one of the chlorides. 39 The same disorder befell Tp*WSCl 2 and related dichalcogenides Tp*WE 2 Cl (E = O, S), and only extended X-ray absorption fine structure (EXAFS) analysis at the W L 3 -edge could distinguish the facial arrangement of these similarly sized ligands.…”

“…The complexes Tp*WOCl 2 and Tp*WSCl 2 were synthesized according to literature procedures. 12,13 Chlorine K-Edge X-ray Absorption Spectroscopy. All data were measured at the Stanford Synchrotron Radiation Lightsource (SSRL) under ring conditions of 3.0 GeV and 400 mA.…”

“…33 Time-dependent (TD-DFT) calculations of chlorine K-pre-edges using the BP86 functional were performed as previously described. 12 Due to the limitations in the accurate treatment of excited states in DFT, absolute transition energies cannot be obtained by this method. Nevertheless, relative transition energies and relative intensities are, in general, reliably modeled.…”

“…The tungsten-sulfido bond is more robust than for molybdenum, and it is highly likely that S tungsten FDHs. 11 Here, the electronic effects of a terminal sulfido ligand are contrasted to an oxo in isostructural Tp*WECl 2 complexes, where Tp* is the hydrotris(3,5dimethylpyrazol-1-yl)borate ligand, 12,13 in a combined spectroscopic and computational study (Scheme 1). X-ray absorption spectroscopy (XAS) at the chlorine K-edge reveals the impact of different terminal chalcogenides on the two chloride ligands that are in an identical cis arrangement to monodentate ligands that complete the coordination sphere in enzymes.…”

An experimental and theoretical study of a heptacoordinated tungsten(VI) complex of a noninnocent phenylenediamine bis(phenolate) ligand

“…[15] For example, the experimental g-values reported for W(V) ions in tungsten enzymes are typically in the range 1.99-1.83 [17], whereas the g-value is even lower for isolated mononuclear sulfido-tungsten(V) model compounds. [18] For 1, the calculated spin density (see below) indicates that the unpaired electron density is delocalized over the ligand.…”