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)(2)Ni(mu-SEt)(2)(mu-Cl)Mn(CO)(3) (7, R = p-MeC6H4CH2; 8, R = EtO2CCH2) and RN(PPh2)(2)Ni(mu-SEt)(2)(mu-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)(2)NiCl2 (3, R = p-MeC6H4CH2; 4, R = EtO2CCH2), and RN(PPh2)(2)Ni(SEt)(2) (5, R = p-MeC6H4CH2; 6, R = EtO2CCH2). The Et3N-assisted aminolysis of Ph2PCl with p-MeC6H4CH2NH2 or EtO2CCH2NH2 center dot 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 center dot 6H(2)O 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)(5)Cl or Mn(CO)(5)Br 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.