Arylformylhydrazone triphenylphosphine Ni(II) complexes: synthesis, crystal structure, and efficient catalysis access to selenophenes

Three arylformylhydrazone triphenylphosphine Ni(II) complexes [X-C₆H₄-(O)C=N-N=C(Me)-CH=C(O)-Ph]Ni(PPh₃) (Ni-1: X = H; Ni-2: X = 4-NO₂; Ni-3: X = 4-CH₃) were synthesized by microwave “one-pot” reaction with arylformylhydrazine, benzoylacetone, triphenylphosphine and Ni(II) chloride hexahydrate. These Ni(II) complexes were systematically characterized using IR, NMR, X-ray single-crystal diffraction, and TGA analysis. Structural determination confirmed that the fully deprotonated arylformylhydrazone acts as a dianionic tridentate (ONO) pincer ligand, coordinating to the center Ni(II) through its oxygen and nitrogen donor atoms. The Ni(II) adopts a distorted square planar coordination geometry, with the triphenylphosphine occupying the fourth coordination site. Importantly, these complexes demonstrated significant catalytic potential in the synthesis of selenophene derivatives from readily available terminal alkynes and elemental selenium. Exceptional catalytic efficiency was achieved at a low loading of 5 mol %.