Cyclopentadienylnickel thiolate complexes: Synthesis, molecular structures and electrochemical detection of sulfur dioxide adducts

Simple reactions between Ni(η⁵-C₅ H₅)(PR₃)Br and the Schiff-base thiols, 4-HSC₆H₄NC(H)C₄H₂ SBr-4′ (1) and 4-HSC₆H₄NC(H)C ₄H₃S (2), or organothiols, HSC₆ H₄F-4 and HSC₆H₄NH₂-4, produced cyclopentadienylnickel thiolates of the formulae, Ni(η⁵-C₅H₅)(PR₃) (SC₆H₄NC(H)C₄H₂SBr-4) (3), Ni(η⁵-C₅H₅)(PR₃) (SC₆H₄NC(H)C₄H₃S) (4) or Ni(η⁵-C₅H₅)(PR₃) (SC₆H₄X-4) (R=Ph, X=F (6) or NH₂ (7) and R=Bu, X=F (5) or NH₂ (8)) which were characterized by a combination of analytical techniques. Complexes 3, 6 and 7 were structurally characterized by X-ray crystallography, showing that they possess the familiar trigonal geometry around the nickel center. These complexes react with sulfur dioxide, with 5, 6, 7 and 8 exhibiting substantial differences between the redox potentials of the pre- and post-SO₂ compounds to suggest that these complexes can be developed as potentiometric SO₂ sensors.