Synthesis, Characterization, and Electrochemistry ofcis-Oxothio- andcis-Bis(thio)tungsten(VI) Complexes of Hydrotris(3,5-dimethylpyrazol-1-yl)borate

Abstract

The complexes TpWO2X react with sulfiding agents such as B2S3 or P4S10 to give the oxothio- and bis(thio)tungsten(VI) complexes TpWOSX (X = Cl(-)) and TpWS2X [X = Cl(-), S2PPh2(-); Tp = hydrotris(3,5-dimethylpyrazol-1-yl)borate]. The reaction of TpWS2Cl with (i) PPh3 in pyridine and (ii) dimethyl sulfoxide affords TpWOSCl in good overall yield. The chloro complexes undergo metathesis with alkali metal salts to yield species of the type TpWOSX and TpWS2X [X = OPh(-), SPh(-), SePh(-), (-)-mentholate]. The diamagnetic complexes exhibit NMR spectra indicative of C(1) (TpWOSX) or C(s) (TpWS2X) symmetry and IR spectra consistent with terminal oxo and thio ligation (nu(W=O), 940-925 cm(-1); nu(W=S) or nu(WS2), 495-475 cm(-1)). Crystals of (R,S)-TpWOS[(-)-mentholate] are monoclinic, space group P2(1), with a = 11.983(2) A, b = 18.100(3) A, c = 13.859(3) A, beta = 91.60(2) degrees, V = 3004.6(8) A(3), and Z = 4. Crystals of TpWS2(OPh)-CH2Cl2 are orthorhombic, space group Pbca, with a = 16.961(4) A, b = 33.098(7) A, c = 9.555(2) A, V = 5364(2) A(3), and Z = 8. The mononuclear, distorted-octahedral tungsten centers are coordinated by a tridentate Tp ligand, an alkoxy or aryloxy ligand, and two terminal chalcogenide ligands. The average W=O and W=S distances are 1.726(7) and 2.125(2) A, respectively, and the O=W=S and S=W=S angles 102.9(3) and 102.9(1) degrees, respectively. The tungsten and sulfur X-ray absorption spectra of TpWOSCl and TpWS2Cl are consistent with the presence of terminal pi-bonded thio ligands in both complexes. The thio complexes generally undergo a reversible one-electron reduction at potentials significantly more positive than their oxo analogues. The chemical, spectroscopic, and electrochemical properties of the complexes are heavily influenced by the presence of W=S pi frontier orbitals.

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

“…400 mV more negative than those of the Tp * WOSX analogues, whereas the reduction potentials of Tp * WOSX complexes are only ca. 50 mV more negative than those of Tp * WS 2 X species [44]. The M(VI)/M(V) reduction potentials of Tp * MoO 2 X complexes are ca.…”

“…In particular, sulfido-W(VI) complexes are more stable, in terms of metal-ligand redox compatibility, than analogous sulfido-Mo(VI) species [44]. However, both elements are capable of facile redox interplay with sulfur-based co-ligands, especially upon oxidation.…”

“…These complexes are effective catalysts for sulfur atom transfer reactions [42,43]. Indeed, the redox stability of W(VI) vs Mo(VI) has facilitated the synthesis of a wide range of oxosulfido-and bis(sulfido)-W(VI) complexes, Tp * WE 2 X (E = O/S; X = monoanion) [44]. The W(VI)/W(V) reduction potentials of Tp * WO 2 X complexes are ca.…”

Kinetics, Mechanism, and Computational Studies of Rhenium-Catalyzed Desulfurization Reactions of Thiiranes (Thioepoxides)

“…Similarly, SAT is observed for a W(O)(S) catalyst, despite thermodynamic preference for the oxo transfer. 46 Qualitative representations of the π and π* levels of W VI d S and W VI dO in W VI (O)(S) have been reported, 46 according to which the energy of the WdO π orbital lies well below the energy of the frontier orbitals. Further, the very high energy of the WdO π* orbital limits nucleophilic attack on the oxo group.…”

“…It is on these terms that one can understand kinetic control favoring SAT over OAT. 46 In the case of Re catalysis, the experimental finding is that SAT provides the exclusive pathway. Calculations of the energetics of the RedE bonds in [MeRe VII (edt)(O)(S)], the monomeric analogue of the putative dirhenium intermediate, gave respective gas-phase RedS and RedO bond strengths of 84 and 118 kcal mol -1 .…”