As the new H-cluster models, a series of N-functionalized azadithiolatodiiron complexes containing mono-and diphosphine ligands 1-7 have been prepared by various methods from complexes [(µ-SCH 2 N(Fun)]Fe 2 (CO) 6 (A, Fun ) C 6 H 4 CHO-p; B, Fun ) C 6 H 4 CO 2 Me-p; C, Fun ) CH 2 CH 2 O 2 CCH 2 C 10 H 7 -1; D, Fun ) CH 2 CH 2 OH) and [(µ-SCH 2 ) 2 N(Fun)]Fe 2 (CO) 5 (Ph 2 PH) (E, Fun ) C 6 H 4 OMe-p). Treatment of A and B with 1 equiv of Me 3 NO • 2H 2 O followed by 1 equiv of Ph 3 P or Ph 2 PH affords the corresponding monophosphine-substituted complexes [(µ-SCH 2 ) 2 N(C 6 H 4 CHO-p)]Fe 2 (CO) 5 (Ph 3 P) (1) and [(µ-SCH 2 ) 2 N(C 6 H 4 CO 2 Me-p)]Fe 2 (CO) 5 L (2, L ) Ph 3 P; 3, Ph 2 PH). Further treatment of B with ca. 1 equiv of Ph 2 PC 2 H 4 PPh 2 (dppe) produced the diphosphine dppe-bridged single model [(µ-SCH 2 ) 2 N(C 6 H 4 CO 2 Mep)]Fe 2 (CO) 4 (dppe) ( 4), whereas C reacts with 1 equiv of Me 3 NO • 2H 2 O followed by 0.5 equiv of (η 5 -Ph 2 PC 5 H 4 ) 2 Fe (dppf) to give the diphosphine dppf-bridged double model [(µ-SCH 2 ) 2 N(CH 2 CH 2 O 2 CCH 2 C 10 H 7 -1)Fe 2 (CO) 5 ] 2 (dppf) (5). While D reacts with 1 equiv of n-BuLi followed by 1 equiv of Ph 2 PCl or directly reacts with 1 equiv of Ph 2 PCl in the presence of Et 3 N to generate N-alkoxyphosphine-substituted complex [(µ-SCH 2 ) 2 N(CH 2 CH 2 OPPh 2 -η 1 )]Fe 2 (CO) 5 ( 6), treatment of E with 1 equiv of n-BuLi followed by 1 equiv of CpFe(CO) 2 I yields organometallic phosphine-substituted complex [(µ-SCH 2 ) 2 N(C 6 H 4 OMep)]Fe 2 (CO) 5 [Ph 2 PFe(CO) 2 Cp] (7). All the new model complexes 1-7 are fully characterized by elemental analysis, spectroscopy, and particularly for 1, 3, 4, 6, and 7 X-ray crystallography. More interestingly, 2 is found to be a catalyst for HOAc proton reduction to hydrogen under CV conditions. In addition, according to electrochemical and spectroelectrochemical studies, an ECEC mechanism is proposed for this electrocatalytic reaction.

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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