Steric and electronic effects of substituents on planar nickel(II) complexes: Synthesis, NMR spectral and single crystal X-ray structural studies on nickel(II) dithiocarbamates with NiS2PN, NiS2PC, and NiS2P2 chromophores

Article abstract of DOI:10.1246/bcsj.79.113

Four new dithiocarbamatonickel(II) complexes [Ni(dchdtc)(NCS)(PPh ₃)] (1), [Ni(dchdtc)(CN)(PPh₃)] (2), [Ni-(dchdtc)(PPh ₃)₂]ClO₄ (3), and [Ni(dchdtc)(dppe)]ClO ₄ (4) (dchdtc = N,N-dicyclohexyldithiocarbamate anion, PPh ₃ = triphenylphosphine, and dppe = 1,2-bis(diphenylphosphino)ethane) were prepared from the parent [Ni(dchdtc)₂]. All four complexes were analyzed by CV, UV-vis, IR, and NMR (¹H, ¹³C, and ³¹P) spectra. ¹³C NMR spectra of the complexes (1-4) show the most notable >N-^...13CS₂ signals at around 200 ppm. In the cyclohexyl ring, the α-CH carbon is deshielded to a greater extent on complexation. Extraordinary deshielding was observed for the ³¹P signal in all of the cases, indicating the effective bonding of phosphorus to the metal center. Single crystal X-ray structural analysis of the mixed ligand complexes (1-3) indicates a decrease in S-Ni-S bite angle when compared to that of the parent bis(dithiocarbamate), due to an increase in steric crowding around the central metal by the introduction of a bulky PPh ₃. The trans effects on Ni-S bonds can be arranged in the following order: NCS^- < PPh₃ < CN^-. The S ₂C-^...N< bond is very short for complex 3, (1.306(3) A), because of the steric effect exerted by two PPh₃ groups and dchdtc. The observed negative reduction potentials follow the order: 1 > 2 > 3, indicating the presence of a higher relative electron density on 1 compared to 2 and 3.