Synthesis, Structural Characterization, and Electrochemical Properties of Dinuclear Ni/Mn Model Complexes for the Active Site of [NiFe]-Hydrogenases

Four new dinuclear Ni/Mn model complexes RN­(PPh2)2Ni­(μ-SEt)2(μ-Cl)­Mn­(CO)3 (7, R = p-MeC6H4CH2; 8, R = EtO2CCH2) and RN­(PPh2)2Ni­(μ-SEt)2(μ-Br)­Mn­(CO)3 (9, R = p-MeC6H4CH2; 10, R = EtO2CCH2) have been prepared via the four separated step-reactions involving six new precursors RN­(PPh2)2 (1, R = p-MeC6H4CH2; 2, R = EtO2CCH2), RN­(PPh2)2NiCl2 (3, R = p-MeC6H4CH2; 4, R = EtO2CCH2), and RN­(PPh2)2Ni­(SEt)2 (5, R = p-MeC6H4CH2; 6, R = EtO2CCH2). The Et3N-assisted aminolysis of Ph2PCl with p-MeC6H4CH2NH2 or EtO2CCH2NH2·HCl in CH2Cl2 gave the azadiphosphine ligands 1 and 2 in 38% and 53% yields, whereas the coordination reaction of 1 or 2 with NiCl2·6H2O in CH2Cl2/MeOH afforded the mononuclear Ni dichloride complexes 3 and 4 in 59% and 78% yields, respectively. While thiolysis of 3 or 4 with EtSH under the assistance of Et3N in CH2Cl2 produced the mononuclear Ni dithiolate complexes 5 and 6 in 64% and 68% yields, further treatment of 5 and 6 with Mn­(CO)5Cl or Mn­(CO)5Br resulted in formation of the dinuclear Ni/Mn model complexes 7–10 in 31–73% yields. All the new compounds 1–10 have been structurally characterized, while model complexes 7 and 9 have been found to be catalysts for HOAc proton reduction to hydrogen under CV conditions.

本研究通过四步分步反应，以六种新型前驱体为原料，合成了4种新型双核镍/锰模型配合物：RN(PPh₂)₂Ni(μ-SEt)₂(μ-Cl)Mn(CO)₃（7，R = 对甲基苄基；8，R = 乙氧羰基甲基）与RN(PPh₂)₂Ni(μ-SEt)₂(μ-Br)Mn(CO)₃（9，R = 对甲基苄基；10，R = 乙氧羰基甲基）。其中六种前驱体分别为：RN(PPh₂)₂（1，R = 对甲基苄基；2，R = 乙氧羰基甲基）、RN(PPh₂)₂NiCl₂（3，R = 对甲基苄基；4，R = 乙氧羰基甲基）以及RN(PPh₂)₂Ni(SEt)₂（5，R = 对甲基苄基；6，R = 乙氧羰基甲基）。以三乙胺（Et₃N）为碱，在二氯甲烷（CH₂Cl₂）中使二苯基氯化膦（Ph₂PCl）分别与对甲基苄胺（p-MeC₆H₄CH₂NH₂）或乙氧羰基甲胺盐酸盐（EtO₂CCH₂NH₂·HCl）发生胺解反应，分别以38%和53%的产率得到氮杂二膦配体1和2；随后将配体1或2与六水合氯化镍（NiCl₂·6H₂O）在二氯甲烷/甲醇（CH₂Cl₂/MeOH）混合溶剂中发生配位反应，分别以59%和78%的产率得到单核二氯化镍配合物3和4。在三乙胺辅助下，于二氯甲烷中使配合物3或4与乙硫醇（EtSH）发生硫解反应，分别以64%和68%的产率得到单核二硫醇合镍配合物5和6；再将配合物5、6分别与五羰基氯化锰（Mn(CO)₅Cl）或五羰基溴化锰（Mn(CO)₅Br）反应，最终以31%~73%的产率得到双核镍/锰模型配合物7~10。所有新型化合物1~10均完成了结构表征，且模型配合物7和9被证实可作为催化剂，在循环伏安法（Cyclic Voltammetry，CV）条件下催化乙酸（HOAc）质子还原产氢。