Synthesis, structures, and some properties of diiron oxadiselenolate (ODSe) and thiodiselenolate (TDSe) complexes as models for the active site of [FeFe]-hydrogenases

摘要

Parent complexes (μ-ODSe)Fe_2(CO)_6 (A, ODSe = SeCH_2OCH_2Se) and (μ-TDSe)Fe_2(CO)_6 (B, TDSe = SeCH_2SCH_2Se) could be prepared by oxidative addition of (HSeCH_2)_2X (X = O, S) with Fe _3(CO)_(12). While reactions of A with 1 equiv of monophosphines in the presence of the decarbonylating agent Me_3NO afforded the corresponding phosphine-monosubstituted complexes (μ-ODSe)Fe_2(CO)_5(L) (1, L = Ph_3P; 2, L = Ph_2POMe), the N-heterocyclic carbene (NHC)-monosubstituted complexes (μ-ODSe)Fe_2(CO)_5(L) (3, L = I_(Mes); 4, L = I_(Mes/Me)) were prepared by reactions of the 1,3-bis(mesityl) imidazolium salt I_(Mes)?HCl and 1-mesityl-3-methylimidazolium salt I_(Mes/Me)?HI with n-BuLi, followed by treatment of the corresponding NHC intermediates with A. The phosphine-containing imidazolium salt I_(Mes/CH2CH2PPh2)?HCl reacted with A in the presence of Me_3NO to give the imidazolium/phosphine-monosubstituted complex (μ-ODSe)Fe_2(CO)_5(I_(Mes/CH2CH2PPh2)?HCl) (5), whereas it reacted with t-BuOK or n-BuLi, followed by treatment of A with the resulting intermediate NHC/phosphine or both the resulting NHC/phosphine and phosphine Ph_2PCH=CH_2, to afford the corresponding NHC/phosphine-disubstituted complex [(μ-ODSe)Fe_2(CO) _5]_2(I_(Mes/CH2CH2PPh2)) (6) and complex 6 along with (μ-ODSe)Fe_2(CO)_5(Ph_2PCH=CH_2) (7), respectively. In addition, 7 could also be produced simply by reaction of 6 with n-BuLi. The phosphine-monosubstituted complexes (μ-TDSe)Fe _2(CO)_5(L) (8, L = Ph_3P; 9, L = Ph _2PH) were similarly prepared by reactions of B with 1 equiv of the corresponding monophosphines in the presence of Me_3NO, whereas reaction of B with m-chloroperoxybenzoic acid afforded the corresponding bridgehead S atom-oxidized complex (μ-TDSeO)Fe_2(CO)_6 (10, TDSeO = SeCH_2S(O)CH_2Se). While complexes A/B and 1-10 were structurally characterized, a comparative study on H_2 production from HOAc catalyzed by parent complexes A/B and their sulfur analogues (μ-ODT)Fe_2(CO)_6/(μ-TDT)Fe _2(CO)_6 was carried out.