Biomimics of [FeFe]‑hydrogenases: Diiron aza- versus oxadiphenylpropanedithiolate complexes with mono- versus diphosphines

To extensively devolep the bioinspired chemistry of [FeFe]‑hydrogenases, this study performs an insigt into the selective substitution of all‑carbonyl diiron aza- versus oxadiphenylpropanedithiolate precursors Fe₂(μ-Ph₂xdt)(CO)₆ (Ph₂xdt = Ph₂odt = (SCHPh)₂O for 1 and Ph₂adt^NH = (SCHPh)₂NH for 2) by mono- versus diphosphines P(C₆H₄R-p)₃ (R = Me and Cl) and (Ph₂P)₂R′ (R′ = cis-CH=CH- for dppv and -CH₂CH₂- for dppe). With monophosphines, their monosubstituted diiron Ph₂odt complexes Fe₂(μ-Ph₂odt)(CO)₅){κ¹-P(C₆H₄R-p)₃} (R = Me for 1a and Cl for 1b) were obtained through the oxidative decarbonylating of 1 at room temperature in MeCN with Me₃NO·2H₂O; in contrast, analogous diiron Ph₂adt^NH complexes Fe₂(μ-Ph₂adt^NH)(CO)₅){κ¹-P(C₆H₄R-p)₃} (R = Me for 2a and Cl for 2b) were afforded via the photolytic decarbonlating of 2 under UV irradiation (365 nm) in toluene. With diphosphines, the dppv-chelated diiron Ph₂xdt complexes Fe₂(μ-Ph₂xdt)(CO)₄(κ²-dppv) (Ph₂xdt = Ph₂odt for 1c and Ph₂adt^NH for 2c) were prepared from the UV-irradiated decarbonylation of 1 or 2 in toluene; by contrast, the dppe-chelated diiron similar complexes Fe₂(μ-Ph₂xdt)(CO)₄(κ²-dppe) (Ph₂xdt = Ph₂odt for 1d and Ph₂adt^NH for 2d) were synthesized from the Me₃NO-assisted decarbonylation of 1 in room-temperature MeCN and that of 2 at refluxing toluene, respectively. The elemental analysis, FT-IR and NMR (¹H, ³¹P) spectroscopy are used for the full elucidation of the molecular structures of these new diiron complexes and X-ray crystallography is applied for further confirmation of 1, 2 and 1a, 2b. The electrochemical properties of representative complexes 1, 1a, 1c and 2, 2a, 2c have been explored and compared with and without acetic acid (AcOH).