Investigations on the Active Site Models of [FeFe]-Hydrogenases: Synthesis, Structure, and Properties of N-Functionalized Azadithiolatodiiron Complexes Containing Mono- and Diphosphine Ligands

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Abstract

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-SCH2N(Fun)]Fe2(CO)6 (A, Fun = C6H4CHO-p; B, Fun = C6H4CO2Me-p; C, Fun = CH2CH2O2CCH2C10H7-1; D, Fun = CH2CH2OH) and [(μ-SCH2)2N(Fun)]Fe2(CO)5(Ph2PH) (E, Fun = C6H4OMe-p). Treatment of A and B with 1 equiv of Me3NO·2H2O followed by 1 equiv of Ph3P or Ph2PH affords the corresponding monophosphine-substituted complexes [(μ-SCH2)2N(C6H4CHO-p)]Fe2(CO)5(Ph3P) (1) and [(μ-SCH2)2N(C6H4CO2Me-p)]Fe2(CO)5L (2, L = Ph3P; 3, Ph2PH). Further treatment of B with ca. 1 equiv of Ph2PC2H4PPh2 (dppe) produced the diphosphine dppe-bridged single model [(μ-SCH2)2N(C6H4CO2Me-p)]Fe2(CO)4(dppe) (4), whereas C reacts with 1 equiv of Me3NO·2H2O followed by 0.5 equiv of (η5-Ph2PC5H4)2Fe (dppf) to give the diphosphine dppf-bridged double model [(μ-SCH2)2N(CH2CH2O2CCH2C10H7-1)Fe2(CO)5]2(dppf) (5). While D reacts with 1 equiv of n-BuLi followed by 1 equiv of Ph2PCl or directly reacts with 1 equiv of Ph2PCl in the presence of Et3N to generate N-alkoxyphosphine-substituted complex [(μ-SCH2)2N(CH2CH2OPPh2-η(1))]Fe2(CO)5 (6), treatment of E with 1 equiv of n-BuLi followed by 1 equiv of CpFe(CO)2I yields organometallic phosphine-substituted complex [(μ-SCH2)2N(C6H4OMe-p)]Fe2(CO)5[Ph2PFe(CO)2Cp] (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.

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