π-Acid/π-Base Carbonyloxo, Carbonylsulfido, and Mixed-Valence Complexes of Tungsten

Carbonyloxotungsten(IV) complexes, Tp*WOX(CO), are produced in the reactions of dioxygen (for X = Cl, Br, I)
or pyridine N-oxide [for X = S2P(OPri)2, S2PPh2] with Tp*WX(CO)2 [Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate]. Analogous carbonylsulfidotungsten(IV) species, Tp*WSX(CO), result from the reactions of Tp*WX(κ2-MeCN)(CO) with propylene sulfide. The carbonyloxo complexes exhibit ν(CO) and ν(WO) IR bands in the 1995−1965
and 957−951 cm-1 regions, respectively; the ν(CO) and ν(WS) bands of the carbonylsulfido species appear at
1970−1937 and 512−502 cm-1, respectively. The complexes possess C1 symmetry and display carbonyl 13C NMR
resonances at δ 272−287, with JWC 160−196 Hz. The crystal structures of Tp*WO(S2PPh2)(CO) and Tp*WS(S2PPh2)(CO)·0.5CHCl3 reveal distorted octahedral tungsten centers coordinated by a fac tridentate Tp* ligand and
mutually cis, monodentate chalcogenido [d(WO) = 1.698(4) Å; d(WS) = 2.135(4) Å], carbonyl, and
dithiophosphinato ligands. In refluxing toluene, Tp*WOI(CO) converts into purple, mixed-valence Tp*WIIII(CO)(μ-O)WVOITp*. The dinuclear complex contains a nearly linear [173.1(6)°] μ-oxo bridge connecting disparate distorted
octahedral tungsten centers. The metrical parameters and spectroscopic properties are consistent with the presence
of a WIII/WV mixed-valence species, possessing a filled, delocalized three-center (W−O−W) π bond and a localized
(on WIII), filled dπ orbital that back-bonds to the carbonyl ligand.