Synthesis, Structures, and Some Properties of Diiron Oxadiselenolate (ODSe) and Thiodiselenolate (TDSe) Complexes as Models for the Active Site of [FeFe]-Hydrogenases

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Abstract

Parent complexes (μ-ODSe)Fe2(CO)6 (A, ODSe = SeCH2OCH2Se) and (μ-TDSe)Fe2(CO)6 (B, TDSe = SeCH2SCH2Se) could be prepared by oxidative addition of (HSeCH2)2X (X = O, S) with Fe3(CO)12. While reactions of A with 1 equiv of monophosphines in the presence of the decarbonylating agent Me3NO afforded the corresponding phosphine-monosubstituted complexes (μ-ODSe)Fe2(CO)5(L) (1, L = Ph3P; 2, L = Ph2POMe), the N-heterocyclic carbene (NHC)-monosubstituted complexes (μ-ODSe)Fe2(CO)5(L) (3, L = IMes; 4, L = IMes/Me) were prepared by reactions of the 1,3-bis(mesityl)imidazolium salt IMes·HCl and 1-mesityl-3-methylimidazolium salt IMes/Me·HI with n-BuLi, followed by treatment of the corresponding NHC intermediates with A. The phosphine-containing imidazolium salt IMes/CH2CH2PPh2·HCl reacted with A in the presence of Me3NO to give the imidazolium/phosphine-monosubstituted complex (μ-ODSe)Fe2(CO)5(IMes/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 Ph2PCH═CH2, to afford the corresponding NHC/phosphine-disubstituted complex [(μ-ODSe)Fe2(CO)5]2(IMes/CH2CH2PPh2) (6) and complex 6 along with (μ-ODSe)Fe2(CO)5(Ph2PCH═CH2) (7), respectively. In addition, 7 could also be produced simply by reaction of 6 with n-BuLi. The phosphine-monosubstituted complexes (μ-TDSe)Fe2(CO)5(L) (8, L = Ph3P; 9, L = Ph2PH) were similarly prepared by reactions of B with 1 equiv of the corresponding monophosphines in the presence of Me3NO, whereas reaction of B with m-chloroperoxybenzoic acid afforded the corresponding bridgehead S atom-oxidized complex (μ-TDSeO)Fe2(CO)6 (10, TDSeO = SeCH2S(O)CH2Se). While complexes A/B and 1–10 were structurally characterized, a comparative study on H2 production from HOAc catalyzed by parent complexes A/B and their sulfur analogues (μ-ODT)Fe2(CO)6/(μ-TDT)Fe2(CO)6 was carried out.

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