Synthetic Challenges toward Modeling Formate Dehydrogenases Using [W^VI≡S] Complexes Supported by a Tetradentate...

This report documents our attempts at synthesizing a terminal [W^VI≡S] complex supported by a tetradentate, diamido/dithiolate ligand ([N₂S₂]^4-). The target compound was selected because it would serve as a synthetic model for the active sites of formate dehydrogenase (FDH) enzymes. Although the desired [N₂S₂]W^VI≡S species was observed as an NEt₃ adduct by mass spectrometry in one case, generally unwanted side reactions prevented isolation and definitive characterization of the target compound. Instead, isolated products characterized by X-ray crystallography included {[N₂S₂]H}W^VI(S₂)Cl from redox chemistry of the terminal sulfide, ([N₂S₂]W^VI)₂(μ-[N₂S₂]) from dissociation of the terminal sulfide, ({[N₂S₂]H}W^V)₂(μ-S)₂ from metal reduction and μ-sulfide bridge formation, and {[N₂S₂]H}₂ from disulfide bond formation via thiolate redox chemistry. A product formed from adventitious exposure to air/moisture, {[N₂S₂]H₂}W^VI(O)₂, was also characterized. The diverse range of products formed simply from attempted metalation of the [N₂S₂]^4- ligand with Cl₄W^VI≡S highlights the synthetic challenges toward building active sites that are structurally faithful to FDH.