Synthesis, structural characterization, and electrochemical properties of (diphosphine)Ni-bridged butterfly Fe2E2 (E = S, Se, Te) cluster complexes related to [NiFe]-hydrogenases

As the active site models of [NiFe]-hydrogenases, a series of trinuclear complexes (diphosphine)Ni(μ3-E)2Fe2(CO)6 (1−10, diphosphine = dppv, dppb, dppf, dppe, (Ph2PCH2)2NR (R = Me, t-Bu; E = S, Se, Te) has been prepared by the one-pot reactions of (μ-E2)Fe2(CO)6 with Et3BHLi, followed by treatment of the resultant intermediates (μ-LiE)2Fe2(CO)6 with the corresponding mononuclear complexes (diphosphine)NiCl2. All the new complexes 1−10 have been fully characterized by elemental analysis, spectroscopy, and X-ray crystallography. Electrochemical study reveals that reductions of the three representative complexes (dppv)Ni(μ3-E)2Fe2(CO)6 (1, E = S; 3, Se; 8, Te) become easier from the S to Se to Te complexes. Furthermore, electrocatalytic study demonstrates that complexes 1, 3, and 8 are catalysts for proton reduction to hydrogen in the presence of proton source HOTs.