Trispyrazolyl Borate Iron Thiolate Complexes and the Dependence of their O2-Reactivity on the Reaction Space

Abstract

The work presented here investigates whether the Tp^MesFe⁺ moiety, which had been previously found to mediate the dioxygenation of cysteine and cysteamine, can do the same with simple thiols, which are not functionalized by an amine group. Accordingly, the complexes Tp^MesFeSR (R=Ph, ⁱPr) were synthesized and after full characterization exposed to O₂. They were found to react unselectively to yield sulfinates, disulfides, and thiosulfones as products. The sulfinate complex Tp^MesFeO₂S-p-Tol was prepared independently and found to be air-stable, suggesting that the additional products are not formed via overoxidation or subsequent reactions of coordinated sulfinate product. To investigate whether the larger reaction space, opened up due to the missing amine donor is responsible, a Tp-ligand functionalized by a pyridyl donor was employed. A corresponding Tp-iron(II) chlorido complex was prepared and converted through salt metathesis reactions into the respective thiolate analogues, which were fully characterized and structurally authenticated. However, subsequent O₂ reactivity studies did not show an improved selectivity. The reason may lie in a more open reaction pocket in combination with an electronic situation which is less ideal than in case of Tp^MesFe(cysteamine).