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

The [N2S2]-type ligand 1,2-(2-C5H4NCH2S)(2)C6H4 (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 center dot 6H(2)O or NiI2 affords the expected new mononuclear Ni complexes Ni[1,2-(2-C5H4NCH2S)(2)C6H4]Cl-2 (1) and Ni[1,2-(2-C5H4NCH2S)(2)C6H4]I-2 (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)(2)C6H4]Br-2 (2) and one unexpected new mononuclear complex Ni[1-(2-C5H4NCH2S)-2-(2-C5H4NCH2SC6H4S)C6H4]Br-2 (2*) in 82% and 5% yields, respectively. More interestingly, the ligand L-containing novel trinuclear NiFe2 complex Ni{[1,2-(2-C5H4NCH2S)(2)C6H4}Fe-2(CO)(6)(mu(3)-S)(2) (4) is found to be prepared by sequential reaction of (mu-S-2)Fe-2(CO)(6) with Et3BHLi, followed by treatment of the resulting (mu-LiS)(2)Fe-2(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.