Synthesis, characterization and some properties of mononuclear Ni and trinuclear NiFe2 complexes related to the active site of [NiFe]-hydrogenases

Abstract

The [N₂S₂]-type ligand 1,2-(2-C₅H₄NCH₂S)₂C₆H₄ (L) is prepared in 84% yield by a new method and its structure has been confirmed by X-ray crystallography. The new synthetic method involves sequential reaction of 1,2-phenylenedithiol with EtONa followed by treatment of the resulting disodium salt of 1,2-phenylenedithiol with in situ generated 2-(chloromethyl)pyridine from its HCl salt. Further treatment of ligand L with NiCl₂·6H₂O or NiI₂ affords the expected new mononuclear Ni complexes Ni[1,2-(2-C₅H₄NCH₂S)₂C₆H₄]Cl₂ (1) and Ni[1,2-(2-C₅H₄NCH₂S)₂C₆H₄]I₂ (3) in 87–88% yields, whereas reaction of L with NiBr₂ under similar conditions results in formation of the expected new mononuclear complex Ni[1,2-(2-C₅H₄NCH₂S)₂C₆H₄]Br₂ (2) and one unexpected new mononuclear complex Ni[1-(2-C₅H₄NCH₂S)-2-(2-C₅H₄NCH₂SC₆H₄S)C₆H₄]Br₂ (2*) in 82% and 5% yields, respectively. More interestingly, the ligand L-containing novel trinuclear NiFe₂ complex Ni{[1,2-(2-C₅H₄NCH₂S)₂C₆H₄}Fe₂(CO)₆(μ₃-S)₂ (4) is found to be prepared by sequential reaction of (μ-S₂)Fe₂(CO)₆ with Et₃BHLi, followed by treatment of the resulting (μ-LiS)₂Fe₂(CO)₆ with mononuclear complex 1, 2, or 3 in 12–20% yields. The new complexes 1–4 and 2* are fully characterized by elemental analysis and various spectroscopies, and the crystal structures of 1, 2* and 3 as well as some electrochemical properties of 1–4 are also reported.