Synthesis of Thiadiazole Dithiolate Metal Complexes Having High Proton Donor Property

Abstract

In order to achieve the proton-coupled electron transfer phenomenon under mild conditions, we have synthesized thiadiazole dithiolate nickel complex 1, as an electron-donor metal complex with highly proton-donating property. The corresponding dianion species could be synthesized in two steps from 3,4-dichloro-2,1,3-thiadiazole. We found that the target nickel complex 1 was isolated as purple needles by the treatment of an aqueous solution of dianion with nitric acid. X-Ray crystallographic analysis revealed that the complex 1 formed a stacked structure in which the intermolecular distance is approximately 3.54 angstrom. N-H proton of 1 forms hydrogen bonding with the oxygen atom of water molecule whereas the unshared electron pair of the sp2 nitrogen atom also forms hydrogen bonding with the proton of water molecule. According to pH dependent UV-Vis spectra of dianion, nickel complex 1 exhibited the high proton-donating property as predicted; both pKa₁ and pKa₂ were estimated to be less than 0. We will report the attempts for preparation of charge transfer complex of 1 and the synthesis of the related metal complexes.