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.