Nickel(II)-Nickel(II) Azadithiolates: Synthesis, Structural Characterization, and Electrocatalytic H-2 Production

摘要

Azadithiolato-bridged dinuclear Ni-2 complexes with the general formula [(eta(5)-C5H5)Ni{(mu-SCH2)(2)NC6H4R-4}Ni(diphos)]BF4 (8-11, R = H, Cl, MeO; diphos = dppv, dppe) have been prepared by a well-designed synthetic method including the following three separate reaction steps. The first reaction step involves preparation of the bis(thioester) precursors 4-RC6H4N(CH2S-(O)CMe)(2) (1-3, R = H, Cl, MeO) by a cocondensation reaction of aniline or its substituted derivatives 4-RC6H4NH2 with 37% aqueous formaldehyde and thioacetic acid. The second step involves preparation of the mononuclear Ni precursors (diphos)Ni[(SCH2)(2)NC6H4R-4] (4-7, R = H, CI, MeO; diphos dppv, dppe) by a one-pot reaction of bis(thioester) precursors 1-3 with t-BuONa followed by treatment of the resulting disodium intermediates 4-RC6H4N(CH2SNa)(2) with (dppv)NiCl2 and (dppe)NiCl2, respectively. The third step involves preparation of the targeted dinuclear Ni-2 complexes 8-11 by coordination reactions of mononuclear Ni precursors 4-7 with [eta(5)-C5H5Ni](- )generated in situ from dissociation of the triple-decker sandwich complex [(C5H6)(3)Ni-2]BF4. While all of the prepared compounds 1-11 have been characterized by elemental analysis and various spectroscopic techniques, the molecular structures of precursor complex 5 and targeted complexes 9 and 11 have been further confirmed by X-ray crystallography. In addition, the two representative targeted complexes 8 and 9 have been found to be catalysts for proton reduction to hydrogen using acetic acid as the proton source under electrochemical conditions.