The use of X-ray photoelectron spectroscopy to assign formal oxidation states in complexes of tungsten (vi), (v) and (iv)

X-ray photoelectron spectra of {[WCl4(NPh)]2}, WCl4(O) and the η2-acetylene complex {[WCl4(η2-PhC2Ph)]2}show W 4f7/2 binding energies (35.8, 37.0 and 35.1 eV, respectively) which are consistent with a formal oxidation state of W(vi). [WCl2(NPh)(NCMe3)(bipy)] and [WCl2(O)(CHC{CH3}3)(PMe3)2] (binding energies 34.2 and 34.1 eV) are also W(vi). The imido complexes [WCl3(NPh)(PMe3)2], {WCl3[NC6H3(Pr2i)-2,6](PMe3)2}, {WCl3[NC6H3(Pr2i)-2,6](dmbipy)} and the η2-acetylene complexes [WCl3(η2-PhC2Ph)(PMe3)2] and [WCl3(η2-PhC2Ph)(PMe2Ph)2] have binding energies in the range 33.6–34.2 eV consistent with tungsten (v). Imido complexes [WCl2(NPh)(PMe3)3],[BPh4][WCl(NPh)(MeCN)(PMe3)2], [WCl2(NPh)(L)(PMe3)3] (L = Me2CCH2, PhC2Ph), {WCl2[NC6H3(Pri)2-2,6](PhC2H)(PMe3)2], {WCl2[NC6H3(Pri)2-2,6](PhC2Ph)(dmbipy)] and [WCl2(NCMe3)(PhC2Ph)(bipy)] have binding energies in the range 32.5–34.0 eV consistent with W(iv). The η2-nitrile complex [WCl2(η2-NCC6H4Me-4)(PMe3)3] (binding energy 32.9 eV) is also W(iv). The range of binding energies for the complexes [WCl4(P)2] (P = PMe3, PMe2Ph and PEt3) and [WCl4(PMe3)3] which are more obviously W(iv) is 33.5–34.4 eV. The η2-acetylene complexes [WCl2(η2-PhC2Ph)(L)(PMe3)2] (L = PMe3, CH2CH2 and CO) and [WCl2(η2-PhC2Ph)(CO)(PMe2Ph)2] have binding energies (range 32.7–33.8 eV) consistent with W(iv). The range of W 4f7/2 binding energies for these complexes confirms that the electron withdrawing properties of ligands are more important in determining core electron level energies than structural considerations.

Graphical abstractW 4f7/2 binding energies obtained from X-ray photoelectron spectra of octahedral tungsten complexes containing organoimido and η2-acetylene ligands and in one case an η2-nitrile ligand, can be used to assign oxidation states with some validity based on the electron withdrawing power of the various ligands surrounding the metal centre.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► XPS gives oxidation states of tungsten organoimido and η2-acetylene complexes. ► W 4f7/2 binding energies are well separated for W(vi), W(v) and W(iv). ► Binding energies depend on ligand electronegativity for W(vi), less so for W(v) and W(iv). ► The oxidation state concept may be used with validity.