Redox Interconversion of Non-Oxido Vanadium Complexes Accompanied by Acid–Base Chemistry of Thiol and Thiolate

Abstract

The redox nature of the non-oxido vanadium sulfur center is associated with several biological systems such as vanadium nitrogenase, the reduction of vanadium ion in ascidians, and the function of amavadin, which is a vanadium(IV) natural product contained in Amanita mushrooms. But the related chemistry is less explored and understood compared to oxido vanadium species due to the oxophilic character of high valent vanadium ions. Herein, we present a class of non-oxido vanadium thiolate complexes, [V(PS2″S)] (1) (PS2″S = [P(CH-3-MeSi-2-S)(CH-3-MeSi-2-SH)]), [V(PS3″)(PS2″S)] (2) (PS3″ = [P(CH-3-MeSi-2-S)]), [V(PS3″)] (3), [V(PS3″)(PS2″S)] (4), and [V(PS3*)] (5a) (PS3* = [P(CH-3-Ph-2-S)]), and study their interconversion through the redox and acid-base reactions. Complex 1 consists of a six-coordinate octahedral vanadium center; complexes 2 and 4 are seven-coordinate with distorted capped trigonal prismatic geometry. Vanadium centers of 3 and 5a are both eight-coordinate; the former adopts ideal dodecahedral geometry, but the latter is better viewed as a distorted square antiprism. Complex 1 is oxidized to complex 2 and then to complex 3 with dioxygen. Each one-electron oxidation process is accompanied by the deprotonation of unbound thiol to bound thiolate. Complex 3 is also produced from complex 2 through stepwise addition of Fe(Cp)/n-BuLi, or in the reverse order. The formation of 2 from 3 is achieved in the order of adding Co(Cp) and acid or, as with the previous complex, inversely. Notably, the reduction of complex 2 to complex 1 accompanying the protonation of bound thiolate to unbound thiol only occurs with the presence of both Co(Cp) and acid, indicating a cooperative effect between the metal-centered reduction and bound thiolate protonation. The conversions among these complexes are observed with ESI-MS and UV-vis-NIR spectroscopies. The work demonstrates two-electron redox interconversion in these complexes mediated by transformations between unbound thiol and bound thiolate.

Activation of O−H and C−O Bonds in Water and Methanol by a Vanadium‐Bound Thiyl Radical

“…However, adding H 2 O to the solution of 1 resulted in a spectral change, as shown in Figure . The final spectrum was analogous to that of [V IV (PS3“)(PS2”S H )] − ( 2 ) (Figure , inset) . The clean transformation was marked by the appearance of an isobestic point at 740 nm.…”

“…The clean transformation was marked by the appearance of an isobestic point at 740 nm. Complex 2 reported previously contains a seven‐coordinate V IV center binding to one PS3“ ligand and one PS2”S H ligand where the thiol group remains unbound . The formation of 2 from the reaction of 1 with H 2 O implies a homolytic cleavage of O−H bond.…”

“…The final spectrumw as analogous to that of [V IV (PS3")(PS2"S H )] À (2) ( Figure 1, inset). [17] The clean transformationw as marked by the appearance of an isobestic point at 740 nm. Complex 2 reported previously contains a seven-coordinate V IV centerb inding to one PS3" ligand and one PS2"S H ligand where the thiol group remains unbound.…”

“…Complex 2 reported previously contains a seven-coordinate V IV centerb inding to one PS3" ligand and one PS2"S H ligand where the thiol group remains unbound. [17] The formationo f2 from the reaction of 1 with H 2 Oi mpliesa homolytic cleavage of OÀHb ond. The ESI-MS measurements combinedw itht he isotope studies further support this hypothesis.…”

“…It is expected that as mall amount of 1 reoccurs because 2 can be oxidized to 1 by dioxygen present in the spectrometer. [17] By reacting with D 2 Oi nstead of H 2 O, the spectrum showed an ion peak around 1195.12 m/z ( Figure S5). The isotope pattern of the peak is consistent with the theoretic one that has the following composi-…”